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Mateusz Guzik a7031f1452 kernel/fork: stop playing lockless games for exe_file replacement 
xchg originated in 6e399cd144 ("prctl: avoid using mmap_sem for exe_file
serialization").  While the commit message does not explain *why* the
change, I found the original submission [1] which ultimately claims it
cleans things up by removing dependency of exe_file on the semaphore.

However, fe69d560b5 ("kernel/fork: always deny write access to current
MM exe_file") added a semaphore up/down cycle to synchronize the state of
exe_file against fork, defeating the point of the original change.

This is on top of semaphore trips already present both in the replacing
function and prctl (the only consumer).

Normally replacing exe_file does not happen for busy processes, thus
write-locking is not an impediment to performance in the intended use
case.  If someone keeps invoking the routine for a busy processes they are
trying to play dirty and that's another reason to avoid any trickery.

As such I think the atomic here only adds complexity for no benefit.

Just write-lock around the replacement.

I also note that replacement races against the mapping check loop as
nothing synchronizes actual assignment with with said checks but I am not
addressing it in this patch.  (Is the loop of any use to begin with?)

Link: https://lore.kernel.org/linux-mm/1424979417.10344.14.camel@stgolabs.net/ [1]
Link: https://lkml.kernel.org/r/20230814172140.1777161-1-mjguzik@gmail.com
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: "Christian Brauner (Microsoft)" <brauner@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 		2023-08-21 13:46:24 -07:00
..
bpf bpf: Repeat check_max_stack_depth for async callbacks 2023-07-18 15:21:09 -07:00
cgroup sched/psi: use kernfs polling functions for PSI trigger polling 2023-07-10 09:52:30 +02:00
configs mm/slab: rename CONFIG_SLAB to CONFIG_SLAB_DEPRECATED 2023-05-26 19:01:47 +02:00
debug kdb: move kdb_send_sig() declaration to a better header file 2023-07-03 09:27:12 +01:00
dma dma-mapping fixes for Linux 6.5 2023-07-09 10:24:22 -07:00
entry ptrace: Provide set/get interface for syscall user dispatch 2023-04-16 14:23:07 +02:00
events cxl for v6.5 2023-07-01 08:58:41 -07:00
futex
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gcov gcov: shut up missing prototype warnings for internal stubs 2023-08-18 10:18:58 -07:00
irq irqdomain: Use return value of strreplace() 2023-06-30 11:13:44 +02:00
kcsan kcsan: Don't expect 64 bits atomic builtins from 32 bits architectures 2023-06-09 23:29:50 +10:00
livepatch livepatch: Make 'klp_stack_entries' static 2023-06-05 13:56:52 +02:00
locking locking/rtmutex: Fix task->pi_waiters integrity 2023-07-17 13:59:10 +02:00
module module: fix init_module_from_file() error handling 2023-07-04 10:17:11 -07:00
power Merge branches 'pm-sleep' and 'pm-qos' 2023-07-14 19:13:21 +02:00
printk seqlock/latch: Provide raw_read_seqcount_latch_retry() 2023-06-05 21:11:03 +02:00
rcu Merge branches 'doc.2023.05.10a', 'fixes.2023.05.11a', 'kvfree.2023.05.10a', 'nocb.2023.05.11a', 'rcu-tasks.2023.05.10a', 'torture.2023.05.15a' and 'rcu-urgent.2023.06.06a' into HEAD 2023-06-07 13:44:06 -07:00
sched sched/psi: use kernfs polling functions for PSI trigger polling 2023-07-10 09:52:30 +02:00
time hardening updates for v6.5-rc1 2023-06-27 21:24:18 -07:00
trace Probe fixes for 6.5-rc3: 2023-07-30 11:27:22 -07:00
.gitignore
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Kconfig.freezer
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Kconfig.hz
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Kconfig.kexec remove ARCH_DEFAULT_KEXEC from Kconfig.kexec 2023-08-18 10:18:55 -07:00
Kconfig.locks
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Kconfig.preempt
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Makefile v6.5-rc1-modules-next 2023-06-28 15:51:08 -07:00
acct.c acct: replace all non-returning strlcpy with strscpy 2023-08-18 10:18:51 -07:00
async.c
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audit.c
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audit.h audit: avoid missing-prototype warnings 2023-05-17 11:34:55 -04:00
audit_fsnotify.c
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audit_tree.c
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audit_watch.c
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auditfilter.c
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auditsc.c capability: just use a 'u64' instead of a 'u32[2]' array 2023-03-01 10:01:22 -08:00
backtracetest.c
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bounds.c
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capability.c capability: fix kernel-doc warnings in capability.c 2023-05-22 14:30:52 -04:00
cfi.c
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compat.c sched_getaffinity: don't assume 'cpumask_size()' is fully initialized 2023-03-14 19:32:38 -07:00
configs.c
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context_tracking.c locking/atomic: treewide: use raw_atomic*_<op>() 2023-06-05 09:57:20 +02:00
cpu.c cpu/hotplug: Fix off by one in cpuhp_bringup_mask() 2023-05-23 18:06:40 +02:00
cpu_pm.c
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crash_core.c mm, treewide: redefine MAX_ORDER sanely 2023-04-05 19:42:46 -07:00
crash_dump.c
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cred.c cred: convert printks to pr_<level> 2023-08-18 10:18:49 -07:00
delayacct.c delayacct: track delays from IRQ/SOFTIRQ 2023-04-18 16:39:34 -07:00
dma.c
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exec_domain.c
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exit.c fork, vhost: Use CLONE_THREAD to fix freezer/ps regression 2023-06-01 17:15:33 -04:00
extable.c
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fail_function.c
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fork.c kernel/fork: stop playing lockless games for exe_file replacement 2023-08-21 13:46:24 -07:00
freezer.c
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gen_kheaders.sh Revert "kheaders: substituting --sort in archive creation" 2023-05-28 16:20:21 +09:00
groups.c
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hung_task.c kernel/hung_task.c: set some hung_task.c variables storage-class-specifier to static 2023-04-08 13:45:37 -07:00
iomem.c
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irq_work.c trace: Add trace_ipi_send_cpu() 2023-03-24 11:01:29 +01:00
jump_label.c
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kallsyms.c kallsyms: strip LTO-only suffixes from promoted global functions 2023-07-12 15:39:34 -07:00
kallsyms_internal.h
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kallsyms_selftest.c kallsyms: Delete an unused parameter related to {module_}kallsyms_on_each_symbol() 2023-03-19 13:27:19 -07:00
kallsyms_selftest.h
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kcmp.c
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kcov.c kcov: add prototypes for helper functions 2023-06-09 17:44:17 -07:00
kexec.c
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kexec_core.c kexec: enable kexec_crash_size to support two crash kernel regions 2023-06-09 17:44:24 -07:00
kexec_elf.c
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kexec_file.c kexec: rename ARCH_HAS_KEXEC_PURGATORY 2023-08-18 10:18:54 -07:00
kexec_internal.h
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kheaders.c kheaders: Use array declaration instead of char 2023-03-24 20:10:59 -07:00
kprobes.c kprobes: Prohibit probing on CFI preamble symbol 2023-07-29 23:32:26 +09:00
ksyms_common.c kallsyms: make kallsyms_show_value() as generic function 2023-06-08 12:27:20 -07:00
ksysfs.c kernel/ksysfs.c: use sysfs_emit for sysfs show handlers 2023-03-24 17:09:14 +01:00
kthread.c kthread: unexport __kthread_should_park() 2023-08-18 10:18:59 -07:00
latencytop.c
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module_signature.c
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notifier.c notifiers: add tracepoints to the notifiers infrastructure 2023-04-08 13:45:38 -07:00
nsproxy.c convert setns(2) to fdget()/fdput() 2023-04-20 22:55:35 -04:00
padata.c padata: use alignment when calculating the number of worker threads 2023-03-14 17:06:44 +08:00
panic.c panic: hide unused global functions 2023-06-09 17:44:15 -07:00
params.c kallsyms: Replace all non-returning strlcpy with strscpy 2023-06-14 12:27:38 -07:00
pid.c pid: use struct_size_t() helper 2023-07-01 08:26:23 -07:00
pid_namespace.c pid: use struct_size_t() helper 2023-07-01 08:26:23 -07:00
pid_sysctl.h kernel: pid_namespace: remove unused set_memfd_noexec_scope() 2023-06-19 16:19:28 -07:00
profile.c
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ptrace.c ptrace: Provide set/get interface for syscall user dispatch 2023-04-16 14:23:07 +02:00
range.c
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reboot.c
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regset.c
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relay.c kernel: relay: remove unnecessary NULL values from relay_open_buf 2023-08-18 10:18:55 -07:00
resource.c
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resource_kunit.c
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rseq.c
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scftorture.c
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scs.c
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seccomp.c seccomp: simplify sysctls with register_sysctl_init() 2023-04-13 11:49:20 -07:00
signal.c signal: print comm and exe name on fatal signals 2023-08-18 10:18:50 -07:00
smp.c trace,smp: Add tracepoints for scheduling remotelly called functions 2023-06-16 22:08:09 +02:00
smpboot.c cpu/hotplug: Remove unused state functions 2023-05-15 13:45:00 +02:00
smpboot.h
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softirq.c Revert "softirq: Let ksoftirqd do its job" 2023-05-09 21:50:27 +02:00
stackleak.c stackleak: allow to specify arch specific stackleak poison function 2023-04-20 11:36:35 +02:00
stacktrace.c
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static_call.c
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static_call_inline.c
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stop_machine.c
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sys.c prctl: move PR_GET_AUXV out of PR_MCE_KILL 2023-07-17 12:53:21 -07:00
sys_ni.c asm-generic updates for 6.5 2023-07-06 10:06:04 -07:00
sysctl-test.c
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sysctl.c v6.5-rc1-sysctl-next 2023-06-28 16:05:21 -07:00
task_work.c
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taskstats.c
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torture.c
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tracepoint.c
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tsacct.c
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ucount.c
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uid16.c
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uid16.h
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umh.c sysctl: fix unused proc_cap_handler() function warning 2023-06-29 15:19:43 -07:00
up.c
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user-return-notifier.c
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user.c
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user_namespace.c
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usermode_driver.c
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utsname.c
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utsname_sysctl.c utsname: simplify one-level sysctl registration for uts_kern_table 2023-04-13 11:49:35 -07:00
vhost_task.c vhost: Fix worker hangs due to missed wake up calls 2023-06-08 15:43:09 -04:00
watch_queue.c watch_queue: prevent dangling pipe pointer 2023-06-06 10:47:04 +02:00
watchdog.c watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check() 2023-08-18 10:19:00 -07:00
watchdog_buddy.c watchdog/hardlockup: move SMP barriers from common code to buddy code 2023-06-19 16:25:28 -07:00
watchdog_perf.c watchdog/perf: add a weak function for an arch to detect if perf can use NMIs 2023-06-09 17:44:21 -07:00
workqueue.c workqueue: Changes for v6.5 2023-06-27 16:32:52 -07:00
workqueue_internal.h workqueue: Automatically mark CPU-hogging work items CPU_INTENSIVE 2023-05-17 17:02:08 -10:00