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![Michal Hocko](/assets/img/avatar_default.png)
copy_process will report any failure in alloc_pid as ENOMEM currently which is misleading because the pid allocation might fail not only when the memory is short but also when the pid space is consumed already. The current man page even mentions this case: : EAGAIN : : A system-imposed limit on the number of threads was encountered. : There are a number of limits that may trigger this error: the : RLIMIT_NPROC soft resource limit (set via setrlimit(2)), which : limits the number of processes and threads for a real user ID, was : reached; the kernel's system-wide limit on the number of processes : and threads, /proc/sys/kernel/threads-max, was reached (see : proc(5)); or the maximum number of PIDs, /proc/sys/kernel/pid_max, : was reached (see proc(5)). so the current behavior is also incorrect wrt. documentation. POSIX man page also suggest returing EAGAIN when the process count limit is reached. This patch simply propagates error code from alloc_pid and makes sure we return -EAGAIN due to reservation failure. This will make behavior of fork closer to both our documentation and POSIX. alloc_pid might alsoo fail when the reaper in the pid namespace is dead (the namespace basically disallows all new processes) and there is no good error code which would match documented ones. We have traditionally returned ENOMEM for this case which is misleading as well but as per Eric W. Biederman this behavior is documented in man pid_namespaces(7) : If the "init" process of a PID namespace terminates, the kernel : terminates all of the processes in the namespace via a SIGKILL signal. : This behavior reflects the fact that the "init" process is essential for : the correct operation of a PID namespace. In this case, a subsequent : fork(2) into this PID namespace will fail with the error ENOMEM; it is : not possible to create a new processes in a PID namespace whose "init" : process has terminated. and introducing a new error code would be too risky so let's stick to ENOMEM for this case. Signed-off-by: Michal Hocko <mhocko@suse.cz> Cc: Oleg Nesterov <oleg@redhat.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
609 lines
15 KiB
C
609 lines
15 KiB
C
/*
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* Generic pidhash and scalable, time-bounded PID allocator
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*
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* (C) 2002-2003 Nadia Yvette Chambers, IBM
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* (C) 2004 Nadia Yvette Chambers, Oracle
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* (C) 2002-2004 Ingo Molnar, Red Hat
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*
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* pid-structures are backing objects for tasks sharing a given ID to chain
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* against. There is very little to them aside from hashing them and
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* parking tasks using given ID's on a list.
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*
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* The hash is always changed with the tasklist_lock write-acquired,
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* and the hash is only accessed with the tasklist_lock at least
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* read-acquired, so there's no additional SMP locking needed here.
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*
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* We have a list of bitmap pages, which bitmaps represent the PID space.
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* Allocating and freeing PIDs is completely lockless. The worst-case
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* allocation scenario when all but one out of 1 million PIDs possible are
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* allocated already: the scanning of 32 list entries and at most PAGE_SIZE
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* bytes. The typical fastpath is a single successful setbit. Freeing is O(1).
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*
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* Pid namespaces:
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* (C) 2007 Pavel Emelyanov <xemul@openvz.org>, OpenVZ, SWsoft Inc.
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* (C) 2007 Sukadev Bhattiprolu <sukadev@us.ibm.com>, IBM
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* Many thanks to Oleg Nesterov for comments and help
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*
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*/
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#include <linux/mm.h>
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#include <linux/export.h>
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#include <linux/slab.h>
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#include <linux/init.h>
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#include <linux/rculist.h>
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#include <linux/bootmem.h>
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#include <linux/hash.h>
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#include <linux/pid_namespace.h>
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#include <linux/init_task.h>
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#include <linux/syscalls.h>
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#include <linux/proc_ns.h>
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#include <linux/proc_fs.h>
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#define pid_hashfn(nr, ns) \
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hash_long((unsigned long)nr + (unsigned long)ns, pidhash_shift)
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static struct hlist_head *pid_hash;
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static unsigned int pidhash_shift = 4;
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struct pid init_struct_pid = INIT_STRUCT_PID;
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int pid_max = PID_MAX_DEFAULT;
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#define RESERVED_PIDS 300
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int pid_max_min = RESERVED_PIDS + 1;
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int pid_max_max = PID_MAX_LIMIT;
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static inline int mk_pid(struct pid_namespace *pid_ns,
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struct pidmap *map, int off)
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{
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return (map - pid_ns->pidmap)*BITS_PER_PAGE + off;
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}
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#define find_next_offset(map, off) \
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find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
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/*
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* PID-map pages start out as NULL, they get allocated upon
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* first use and are never deallocated. This way a low pid_max
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* value does not cause lots of bitmaps to be allocated, but
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* the scheme scales to up to 4 million PIDs, runtime.
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*/
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struct pid_namespace init_pid_ns = {
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.kref = {
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.refcount = ATOMIC_INIT(2),
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},
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.pidmap = {
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[ 0 ... PIDMAP_ENTRIES-1] = { ATOMIC_INIT(BITS_PER_PAGE), NULL }
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},
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.last_pid = 0,
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.nr_hashed = PIDNS_HASH_ADDING,
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.level = 0,
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.child_reaper = &init_task,
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.user_ns = &init_user_ns,
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.ns.inum = PROC_PID_INIT_INO,
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#ifdef CONFIG_PID_NS
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.ns.ops = &pidns_operations,
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#endif
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};
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EXPORT_SYMBOL_GPL(init_pid_ns);
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/*
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* Note: disable interrupts while the pidmap_lock is held as an
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* interrupt might come in and do read_lock(&tasklist_lock).
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*
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* If we don't disable interrupts there is a nasty deadlock between
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* detach_pid()->free_pid() and another cpu that does
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* spin_lock(&pidmap_lock) followed by an interrupt routine that does
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* read_lock(&tasklist_lock);
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*
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* After we clean up the tasklist_lock and know there are no
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* irq handlers that take it we can leave the interrupts enabled.
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* For now it is easier to be safe than to prove it can't happen.
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*/
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static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
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static void free_pidmap(struct upid *upid)
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{
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int nr = upid->nr;
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struct pidmap *map = upid->ns->pidmap + nr / BITS_PER_PAGE;
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int offset = nr & BITS_PER_PAGE_MASK;
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clear_bit(offset, map->page);
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atomic_inc(&map->nr_free);
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}
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/*
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* If we started walking pids at 'base', is 'a' seen before 'b'?
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*/
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static int pid_before(int base, int a, int b)
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{
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/*
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* This is the same as saying
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*
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* (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT
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* and that mapping orders 'a' and 'b' with respect to 'base'.
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*/
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return (unsigned)(a - base) < (unsigned)(b - base);
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}
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/*
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* We might be racing with someone else trying to set pid_ns->last_pid
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* at the pid allocation time (there's also a sysctl for this, but racing
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* with this one is OK, see comment in kernel/pid_namespace.c about it).
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* We want the winner to have the "later" value, because if the
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* "earlier" value prevails, then a pid may get reused immediately.
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*
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* Since pids rollover, it is not sufficient to just pick the bigger
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* value. We have to consider where we started counting from.
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*
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* 'base' is the value of pid_ns->last_pid that we observed when
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* we started looking for a pid.
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*
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* 'pid' is the pid that we eventually found.
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*/
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static void set_last_pid(struct pid_namespace *pid_ns, int base, int pid)
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{
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int prev;
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int last_write = base;
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do {
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prev = last_write;
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last_write = cmpxchg(&pid_ns->last_pid, prev, pid);
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} while ((prev != last_write) && (pid_before(base, last_write, pid)));
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}
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static int alloc_pidmap(struct pid_namespace *pid_ns)
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{
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int i, offset, max_scan, pid, last = pid_ns->last_pid;
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struct pidmap *map;
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pid = last + 1;
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if (pid >= pid_max)
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pid = RESERVED_PIDS;
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offset = pid & BITS_PER_PAGE_MASK;
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map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
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/*
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* If last_pid points into the middle of the map->page we
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* want to scan this bitmap block twice, the second time
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* we start with offset == 0 (or RESERVED_PIDS).
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*/
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max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
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for (i = 0; i <= max_scan; ++i) {
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if (unlikely(!map->page)) {
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void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
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/*
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* Free the page if someone raced with us
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* installing it:
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*/
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spin_lock_irq(&pidmap_lock);
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if (!map->page) {
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map->page = page;
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page = NULL;
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}
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spin_unlock_irq(&pidmap_lock);
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kfree(page);
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if (unlikely(!map->page))
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return -ENOMEM;
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}
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if (likely(atomic_read(&map->nr_free))) {
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for ( ; ; ) {
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if (!test_and_set_bit(offset, map->page)) {
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atomic_dec(&map->nr_free);
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set_last_pid(pid_ns, last, pid);
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return pid;
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}
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offset = find_next_offset(map, offset);
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if (offset >= BITS_PER_PAGE)
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break;
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pid = mk_pid(pid_ns, map, offset);
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if (pid >= pid_max)
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break;
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}
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}
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if (map < &pid_ns->pidmap[(pid_max-1)/BITS_PER_PAGE]) {
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++map;
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offset = 0;
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} else {
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map = &pid_ns->pidmap[0];
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offset = RESERVED_PIDS;
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if (unlikely(last == offset))
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break;
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}
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pid = mk_pid(pid_ns, map, offset);
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}
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return -EAGAIN;
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}
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int next_pidmap(struct pid_namespace *pid_ns, unsigned int last)
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{
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int offset;
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struct pidmap *map, *end;
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if (last >= PID_MAX_LIMIT)
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return -1;
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offset = (last + 1) & BITS_PER_PAGE_MASK;
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map = &pid_ns->pidmap[(last + 1)/BITS_PER_PAGE];
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end = &pid_ns->pidmap[PIDMAP_ENTRIES];
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for (; map < end; map++, offset = 0) {
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if (unlikely(!map->page))
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continue;
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offset = find_next_bit((map)->page, BITS_PER_PAGE, offset);
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if (offset < BITS_PER_PAGE)
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return mk_pid(pid_ns, map, offset);
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}
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return -1;
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}
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void put_pid(struct pid *pid)
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{
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struct pid_namespace *ns;
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if (!pid)
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return;
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ns = pid->numbers[pid->level].ns;
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if ((atomic_read(&pid->count) == 1) ||
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atomic_dec_and_test(&pid->count)) {
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kmem_cache_free(ns->pid_cachep, pid);
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put_pid_ns(ns);
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}
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}
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EXPORT_SYMBOL_GPL(put_pid);
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static void delayed_put_pid(struct rcu_head *rhp)
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{
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struct pid *pid = container_of(rhp, struct pid, rcu);
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put_pid(pid);
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}
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void free_pid(struct pid *pid)
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{
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/* We can be called with write_lock_irq(&tasklist_lock) held */
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int i;
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unsigned long flags;
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spin_lock_irqsave(&pidmap_lock, flags);
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for (i = 0; i <= pid->level; i++) {
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struct upid *upid = pid->numbers + i;
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struct pid_namespace *ns = upid->ns;
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hlist_del_rcu(&upid->pid_chain);
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switch(--ns->nr_hashed) {
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case 2:
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case 1:
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/* When all that is left in the pid namespace
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* is the reaper wake up the reaper. The reaper
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* may be sleeping in zap_pid_ns_processes().
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*/
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wake_up_process(ns->child_reaper);
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break;
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case PIDNS_HASH_ADDING:
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/* Handle a fork failure of the first process */
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WARN_ON(ns->child_reaper);
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ns->nr_hashed = 0;
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/* fall through */
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case 0:
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schedule_work(&ns->proc_work);
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break;
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}
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}
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spin_unlock_irqrestore(&pidmap_lock, flags);
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for (i = 0; i <= pid->level; i++)
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free_pidmap(pid->numbers + i);
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call_rcu(&pid->rcu, delayed_put_pid);
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}
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struct pid *alloc_pid(struct pid_namespace *ns)
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{
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struct pid *pid;
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enum pid_type type;
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int i, nr;
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struct pid_namespace *tmp;
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struct upid *upid;
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int retval = -ENOMEM;
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pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
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if (!pid)
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return ERR_PTR(retval);
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tmp = ns;
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pid->level = ns->level;
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for (i = ns->level; i >= 0; i--) {
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nr = alloc_pidmap(tmp);
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if (IS_ERR_VALUE(nr)) {
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retval = nr;
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goto out_free;
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}
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pid->numbers[i].nr = nr;
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pid->numbers[i].ns = tmp;
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tmp = tmp->parent;
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}
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if (unlikely(is_child_reaper(pid))) {
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if (pid_ns_prepare_proc(ns))
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goto out_free;
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}
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get_pid_ns(ns);
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atomic_set(&pid->count, 1);
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for (type = 0; type < PIDTYPE_MAX; ++type)
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INIT_HLIST_HEAD(&pid->tasks[type]);
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upid = pid->numbers + ns->level;
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spin_lock_irq(&pidmap_lock);
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if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
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goto out_unlock;
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for ( ; upid >= pid->numbers; --upid) {
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hlist_add_head_rcu(&upid->pid_chain,
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&pid_hash[pid_hashfn(upid->nr, upid->ns)]);
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upid->ns->nr_hashed++;
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}
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spin_unlock_irq(&pidmap_lock);
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return pid;
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out_unlock:
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spin_unlock_irq(&pidmap_lock);
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put_pid_ns(ns);
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out_free:
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while (++i <= ns->level)
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free_pidmap(pid->numbers + i);
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kmem_cache_free(ns->pid_cachep, pid);
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return ERR_PTR(retval);
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}
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void disable_pid_allocation(struct pid_namespace *ns)
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{
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spin_lock_irq(&pidmap_lock);
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ns->nr_hashed &= ~PIDNS_HASH_ADDING;
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spin_unlock_irq(&pidmap_lock);
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}
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struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
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{
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struct upid *pnr;
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hlist_for_each_entry_rcu(pnr,
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&pid_hash[pid_hashfn(nr, ns)], pid_chain)
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if (pnr->nr == nr && pnr->ns == ns)
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return container_of(pnr, struct pid,
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numbers[ns->level]);
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return NULL;
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}
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EXPORT_SYMBOL_GPL(find_pid_ns);
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struct pid *find_vpid(int nr)
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{
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return find_pid_ns(nr, task_active_pid_ns(current));
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}
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EXPORT_SYMBOL_GPL(find_vpid);
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/*
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* attach_pid() must be called with the tasklist_lock write-held.
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*/
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void attach_pid(struct task_struct *task, enum pid_type type)
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{
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struct pid_link *link = &task->pids[type];
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hlist_add_head_rcu(&link->node, &link->pid->tasks[type]);
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}
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static void __change_pid(struct task_struct *task, enum pid_type type,
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struct pid *new)
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{
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struct pid_link *link;
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struct pid *pid;
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int tmp;
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link = &task->pids[type];
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pid = link->pid;
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hlist_del_rcu(&link->node);
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link->pid = new;
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for (tmp = PIDTYPE_MAX; --tmp >= 0; )
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if (!hlist_empty(&pid->tasks[tmp]))
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return;
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free_pid(pid);
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}
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void detach_pid(struct task_struct *task, enum pid_type type)
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{
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__change_pid(task, type, NULL);
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}
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void change_pid(struct task_struct *task, enum pid_type type,
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struct pid *pid)
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{
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__change_pid(task, type, pid);
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attach_pid(task, type);
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}
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/* transfer_pid is an optimization of attach_pid(new), detach_pid(old) */
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void transfer_pid(struct task_struct *old, struct task_struct *new,
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enum pid_type type)
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{
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new->pids[type].pid = old->pids[type].pid;
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hlist_replace_rcu(&old->pids[type].node, &new->pids[type].node);
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}
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struct task_struct *pid_task(struct pid *pid, enum pid_type type)
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{
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struct task_struct *result = NULL;
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if (pid) {
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struct hlist_node *first;
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first = rcu_dereference_check(hlist_first_rcu(&pid->tasks[type]),
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lockdep_tasklist_lock_is_held());
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if (first)
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result = hlist_entry(first, struct task_struct, pids[(type)].node);
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}
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return result;
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}
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EXPORT_SYMBOL(pid_task);
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/*
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* Must be called under rcu_read_lock().
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*/
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struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
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{
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rcu_lockdep_assert(rcu_read_lock_held(),
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"find_task_by_pid_ns() needs rcu_read_lock()"
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" protection");
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return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
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}
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struct task_struct *find_task_by_vpid(pid_t vnr)
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{
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return find_task_by_pid_ns(vnr, task_active_pid_ns(current));
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}
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struct pid *get_task_pid(struct task_struct *task, enum pid_type type)
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{
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struct pid *pid;
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rcu_read_lock();
|
|
if (type != PIDTYPE_PID)
|
|
task = task->group_leader;
|
|
pid = get_pid(task->pids[type].pid);
|
|
rcu_read_unlock();
|
|
return pid;
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_task_pid);
|
|
|
|
struct task_struct *get_pid_task(struct pid *pid, enum pid_type type)
|
|
{
|
|
struct task_struct *result;
|
|
rcu_read_lock();
|
|
result = pid_task(pid, type);
|
|
if (result)
|
|
get_task_struct(result);
|
|
rcu_read_unlock();
|
|
return result;
|
|
}
|
|
EXPORT_SYMBOL_GPL(get_pid_task);
|
|
|
|
struct pid *find_get_pid(pid_t nr)
|
|
{
|
|
struct pid *pid;
|
|
|
|
rcu_read_lock();
|
|
pid = get_pid(find_vpid(nr));
|
|
rcu_read_unlock();
|
|
|
|
return pid;
|
|
}
|
|
EXPORT_SYMBOL_GPL(find_get_pid);
|
|
|
|
pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
|
|
{
|
|
struct upid *upid;
|
|
pid_t nr = 0;
|
|
|
|
if (pid && ns->level <= pid->level) {
|
|
upid = &pid->numbers[ns->level];
|
|
if (upid->ns == ns)
|
|
nr = upid->nr;
|
|
}
|
|
return nr;
|
|
}
|
|
EXPORT_SYMBOL_GPL(pid_nr_ns);
|
|
|
|
pid_t pid_vnr(struct pid *pid)
|
|
{
|
|
return pid_nr_ns(pid, task_active_pid_ns(current));
|
|
}
|
|
EXPORT_SYMBOL_GPL(pid_vnr);
|
|
|
|
pid_t __task_pid_nr_ns(struct task_struct *task, enum pid_type type,
|
|
struct pid_namespace *ns)
|
|
{
|
|
pid_t nr = 0;
|
|
|
|
rcu_read_lock();
|
|
if (!ns)
|
|
ns = task_active_pid_ns(current);
|
|
if (likely(pid_alive(task))) {
|
|
if (type != PIDTYPE_PID)
|
|
task = task->group_leader;
|
|
nr = pid_nr_ns(task->pids[type].pid, ns);
|
|
}
|
|
rcu_read_unlock();
|
|
|
|
return nr;
|
|
}
|
|
EXPORT_SYMBOL(__task_pid_nr_ns);
|
|
|
|
pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns)
|
|
{
|
|
return pid_nr_ns(task_tgid(tsk), ns);
|
|
}
|
|
EXPORT_SYMBOL(task_tgid_nr_ns);
|
|
|
|
struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
|
|
{
|
|
return ns_of_pid(task_pid(tsk));
|
|
}
|
|
EXPORT_SYMBOL_GPL(task_active_pid_ns);
|
|
|
|
/*
|
|
* Used by proc to find the first pid that is greater than or equal to nr.
|
|
*
|
|
* If there is a pid at nr this function is exactly the same as find_pid_ns.
|
|
*/
|
|
struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
|
|
{
|
|
struct pid *pid;
|
|
|
|
do {
|
|
pid = find_pid_ns(nr, ns);
|
|
if (pid)
|
|
break;
|
|
nr = next_pidmap(ns, nr);
|
|
} while (nr > 0);
|
|
|
|
return pid;
|
|
}
|
|
|
|
/*
|
|
* The pid hash table is scaled according to the amount of memory in the
|
|
* machine. From a minimum of 16 slots up to 4096 slots at one gigabyte or
|
|
* more.
|
|
*/
|
|
void __init pidhash_init(void)
|
|
{
|
|
unsigned int i, pidhash_size;
|
|
|
|
pid_hash = alloc_large_system_hash("PID", sizeof(*pid_hash), 0, 18,
|
|
HASH_EARLY | HASH_SMALL,
|
|
&pidhash_shift, NULL,
|
|
0, 4096);
|
|
pidhash_size = 1U << pidhash_shift;
|
|
|
|
for (i = 0; i < pidhash_size; i++)
|
|
INIT_HLIST_HEAD(&pid_hash[i]);
|
|
}
|
|
|
|
void __init pidmap_init(void)
|
|
{
|
|
/* Veryify no one has done anything silly */
|
|
BUILD_BUG_ON(PID_MAX_LIMIT >= PIDNS_HASH_ADDING);
|
|
|
|
/* bump default and minimum pid_max based on number of cpus */
|
|
pid_max = min(pid_max_max, max_t(int, pid_max,
|
|
PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
|
|
pid_max_min = max_t(int, pid_max_min,
|
|
PIDS_PER_CPU_MIN * num_possible_cpus());
|
|
pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
|
|
|
|
init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
|
|
/* Reserve PID 0. We never call free_pidmap(0) */
|
|
set_bit(0, init_pid_ns.pidmap[0].page);
|
|
atomic_dec(&init_pid_ns.pidmap[0].nr_free);
|
|
|
|
init_pid_ns.pid_cachep = KMEM_CACHE(pid,
|
|
SLAB_HWCACHE_ALIGN | SLAB_PANIC);
|
|
}
|