Messages in this thread Patch in this message | | | Date | Fri, 16 Mar 2012 16:34:50 -0700 | From | Greg KH <> | Subject | [ 03/38] aio: fix the "too late munmap()" race |
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3.0-stable review patch. If anyone has any objections, please let me know.
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From: Al Viro <viro@ZenIV.linux.org.uk>
commit c7b285550544c22bc005ec20978472c9ac7138c6 upstream.
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> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/aio.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-)
--- a/fs/aio.c +++ b/fs/aio.c @@ -228,12 +228,6 @@ static void __put_ioctx(struct kioctx *c 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); @@ -527,11 +521,16 @@ static void aio_fput_routine(struct work 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); @@ -562,7 +561,6 @@ static int __aio_put_req(struct kioctx * * 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);
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