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authorAl Viro <viro@ZenIV.linux.org.uk>2012-03-08 17:51:19 +0000
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-09 18:59:59 -0800
commitc7b285550544c22bc005ec20978472c9ac7138c6 (patch)
tree2115cba489066af001312bf93d9f07321e25bf12
parent86b62a2cb4fc09037bbce2959d2992962396fd7f (diff)
aio: fix the "too late munmap()" race
Current code has put_ioctx() called asynchronously from aio_fput_routine(); that's done *after* we have killed the request that used to pin ioctx, so there's nothing to stop io_destroy() waiting in wait_for_all_aios() from progressing. As the result, we can end up with async call of put_ioctx() being the last one and possibly happening during exit_mmap() or elf_core_dump(), neither of which expects stray munmap() being done to them... We do need to prevent _freeing_ ioctx until aio_fput_routine() is done with that, but that's all we care about - neither io_destroy() nor exit_aio() will progress past wait_for_all_aios() until aio_fput_routine() does really_put_req(), so the ioctx teardown won't be done until then and we don't care about the contents of ioctx past that point. Since actual freeing of these suckers is RCU-delayed, we don't need to bump ioctx refcount when request goes into list for async removal. All we need is rcu_read_lock held just over the ->ctx_lock-protected area in aio_fput_routine(). Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Reviewed-by: Jeff Moyer <jmoyer@redhat.com> Acked-by: Benjamin LaHaise <bcrl@kvack.org> Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/aio.c14
1 files changed, 6 insertions, 8 deletions
diff --git a/fs/aio.c b/fs/aio.c
index f6578cb22d00..b9d64d89a043 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -228,12 +228,6 @@ static void __put_ioctx(struct kioctx *ctx)
call_rcu(&ctx->rcu_head, ctx_rcu_free);
}
-static inline void get_ioctx(struct kioctx *kioctx)
-{
- BUG_ON(atomic_read(&kioctx->users) <= 0);
- atomic_inc(&kioctx->users);
-}
-
static inline int try_get_ioctx(struct kioctx *kioctx)
{
return atomic_inc_not_zero(&kioctx->users);
@@ -609,11 +603,16 @@ static void aio_fput_routine(struct work_struct *data)
fput(req->ki_filp);
/* Link the iocb into the context's free list */
+ rcu_read_lock();
spin_lock_irq(&ctx->ctx_lock);
really_put_req(ctx, req);
+ /*
+ * at that point ctx might've been killed, but actual
+ * freeing is RCU'd
+ */
spin_unlock_irq(&ctx->ctx_lock);
+ rcu_read_unlock();
- put_ioctx(ctx);
spin_lock_irq(&fput_lock);
}
spin_unlock_irq(&fput_lock);
@@ -644,7 +643,6 @@ static int __aio_put_req(struct kioctx *ctx, struct kiocb *req)
* this function will be executed w/out any aio kthread wakeup.
*/
if (unlikely(!fput_atomic(req->ki_filp))) {
- get_ioctx(ctx);
spin_lock(&fput_lock);
list_add(&req->ki_list, &fput_head);
spin_unlock(&fput_lock);