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author | Al Viro <viro@ZenIV.linux.org.uk> | 2012-03-08 17:51:19 +0000 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-03-09 18:59:59 -0800 |
commit | c7b285550544c22bc005ec20978472c9ac7138c6 (patch) | |
tree | 2115cba489066af001312bf93d9f07321e25bf12 | |
parent | 86b62a2cb4fc09037bbce2959d2992962396fd7f (diff) | |
download | op-kernel-dev-c7b285550544c22bc005ec20978472c9ac7138c6.zip op-kernel-dev-c7b285550544c22bc005ec20978472c9ac7138c6.tar.gz |
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.c | 14 |
1 files changed, 6 insertions, 8 deletions
@@ -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); |