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![Vadim Lobanov](/assets/img/avatar_default.png)
Christoph Hellwig has expressed concerns that the recent fdtable changes expose the details of the RCU methodology used to release no-longer-used fdtable structures to the rest of the kernel. The trivial patch below addresses these concerns by introducing the appropriate free_fdtable() calls, which simply wrap the release RCU usage. Since free_fdtable() is a one-liner, it makes sense to promote it to an inline helper. Signed-off-by: Vadim Lobanov <vlobanov@speakeasy.net> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
256 lines
6.3 KiB
C
256 lines
6.3 KiB
C
/*
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* linux/fs/file.c
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*
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* Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
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*
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* Manage the dynamic fd arrays in the process files_struct.
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*/
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#include <linux/fs.h>
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#include <linux/mm.h>
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#include <linux/time.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/file.h>
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#include <linux/bitops.h>
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#include <linux/interrupt.h>
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#include <linux/spinlock.h>
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#include <linux/rcupdate.h>
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#include <linux/workqueue.h>
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struct fdtable_defer {
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spinlock_t lock;
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struct work_struct wq;
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struct fdtable *next;
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};
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/*
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* We use this list to defer free fdtables that have vmalloced
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* sets/arrays. By keeping a per-cpu list, we avoid having to embed
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* the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
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* this per-task structure.
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*/
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static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
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static inline void * alloc_fdmem(unsigned int size)
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{
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if (size <= PAGE_SIZE)
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return kmalloc(size, GFP_KERNEL);
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else
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return vmalloc(size);
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}
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static inline void free_fdarr(struct fdtable *fdt)
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{
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if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
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kfree(fdt->fd);
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else
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vfree(fdt->fd);
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}
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static inline void free_fdset(struct fdtable *fdt)
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{
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if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
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kfree(fdt->open_fds);
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else
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vfree(fdt->open_fds);
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}
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static void free_fdtable_work(struct work_struct *work)
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{
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struct fdtable_defer *f =
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container_of(work, struct fdtable_defer, wq);
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struct fdtable *fdt;
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spin_lock_bh(&f->lock);
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fdt = f->next;
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f->next = NULL;
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spin_unlock_bh(&f->lock);
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while(fdt) {
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struct fdtable *next = fdt->next;
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vfree(fdt->fd);
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free_fdset(fdt);
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kfree(fdt);
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fdt = next;
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}
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}
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void free_fdtable_rcu(struct rcu_head *rcu)
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{
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struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
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struct fdtable_defer *fddef;
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BUG_ON(!fdt);
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if (fdt->max_fds <= NR_OPEN_DEFAULT) {
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/*
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* This fdtable is embedded in the files structure and that
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* structure itself is getting destroyed.
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*/
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kmem_cache_free(files_cachep,
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container_of(fdt, struct files_struct, fdtab));
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return;
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}
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if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {
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kfree(fdt->fd);
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kfree(fdt->open_fds);
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kfree(fdt);
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} else {
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fddef = &get_cpu_var(fdtable_defer_list);
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spin_lock(&fddef->lock);
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fdt->next = fddef->next;
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fddef->next = fdt;
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/* vmallocs are handled from the workqueue context */
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schedule_work(&fddef->wq);
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spin_unlock(&fddef->lock);
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put_cpu_var(fdtable_defer_list);
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}
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}
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/*
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* Expand the fdset in the files_struct. Called with the files spinlock
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* held for write.
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*/
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static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
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{
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unsigned int cpy, set;
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BUG_ON(nfdt->max_fds < ofdt->max_fds);
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if (ofdt->max_fds == 0)
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return;
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cpy = ofdt->max_fds * sizeof(struct file *);
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set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
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memcpy(nfdt->fd, ofdt->fd, cpy);
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memset((char *)(nfdt->fd) + cpy, 0, set);
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cpy = ofdt->max_fds / BITS_PER_BYTE;
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set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
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memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
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memset((char *)(nfdt->open_fds) + cpy, 0, set);
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memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
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memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
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}
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static struct fdtable * alloc_fdtable(unsigned int nr)
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{
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struct fdtable *fdt;
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char *data;
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/*
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* Figure out how many fds we actually want to support in this fdtable.
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* Allocation steps are keyed to the size of the fdarray, since it
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* grows far faster than any of the other dynamic data. We try to fit
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* the fdarray into comfortable page-tuned chunks: starting at 1024B
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* and growing in powers of two from there on.
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*/
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nr /= (1024 / sizeof(struct file *));
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nr = roundup_pow_of_two(nr + 1);
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nr *= (1024 / sizeof(struct file *));
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if (nr > NR_OPEN)
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nr = NR_OPEN;
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fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
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if (!fdt)
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goto out;
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fdt->max_fds = nr;
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data = alloc_fdmem(nr * sizeof(struct file *));
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if (!data)
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goto out_fdt;
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fdt->fd = (struct file **)data;
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data = alloc_fdmem(max_t(unsigned int,
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2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
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if (!data)
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goto out_arr;
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fdt->open_fds = (fd_set *)data;
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data += nr / BITS_PER_BYTE;
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fdt->close_on_exec = (fd_set *)data;
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INIT_RCU_HEAD(&fdt->rcu);
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fdt->next = NULL;
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return fdt;
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out_arr:
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free_fdarr(fdt);
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out_fdt:
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kfree(fdt);
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out:
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return NULL;
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}
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/*
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* Expand the file descriptor table.
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* This function will allocate a new fdtable and both fd array and fdset, of
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* the given size.
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* Return <0 error code on error; 1 on successful completion.
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* The files->file_lock should be held on entry, and will be held on exit.
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*/
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static int expand_fdtable(struct files_struct *files, int nr)
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__releases(files->file_lock)
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__acquires(files->file_lock)
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{
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struct fdtable *new_fdt, *cur_fdt;
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spin_unlock(&files->file_lock);
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new_fdt = alloc_fdtable(nr);
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spin_lock(&files->file_lock);
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if (!new_fdt)
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return -ENOMEM;
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/*
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* Check again since another task may have expanded the fd table while
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* we dropped the lock
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*/
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cur_fdt = files_fdtable(files);
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if (nr >= cur_fdt->max_fds) {
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/* Continue as planned */
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copy_fdtable(new_fdt, cur_fdt);
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rcu_assign_pointer(files->fdt, new_fdt);
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if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
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free_fdtable(cur_fdt);
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} else {
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/* Somebody else expanded, so undo our attempt */
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free_fdarr(new_fdt);
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free_fdset(new_fdt);
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kfree(new_fdt);
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}
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return 1;
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}
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/*
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* Expand files.
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* This function will expand the file structures, if the requested size exceeds
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* the current capacity and there is room for expansion.
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* Return <0 error code on error; 0 when nothing done; 1 when files were
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* expanded and execution may have blocked.
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* The files->file_lock should be held on entry, and will be held on exit.
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*/
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int expand_files(struct files_struct *files, int nr)
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{
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struct fdtable *fdt;
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fdt = files_fdtable(files);
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/* Do we need to expand? */
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if (nr < fdt->max_fds)
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return 0;
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/* Can we expand? */
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if (nr >= NR_OPEN)
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return -EMFILE;
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/* All good, so we try */
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return expand_fdtable(files, nr);
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}
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static void __devinit fdtable_defer_list_init(int cpu)
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{
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struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
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spin_lock_init(&fddef->lock);
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INIT_WORK(&fddef->wq, free_fdtable_work);
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fddef->next = NULL;
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}
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void __init files_defer_init(void)
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{
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int i;
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for_each_possible_cpu(i)
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fdtable_defer_list_init(i);
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}
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