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IB/umem: Fix possible hang on process exit

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If ib_umem_release() is called after ib_uverbs_close() sets context->closing,
then a process can get stuck in a D state, because the code boils down to

	if (down_write_trylock(&mm->mmap_sem))
		down_write(&mm->mmap_sem);

which is obviously a stupid instant deadlock.  Fix the code so that we
only try to take the lock once.

This bug was introduced in commit f7c6a7b5 ("IB/uverbs: Export
ib_umem_get()/ib_umem_release() to modules") which fortunately never
made it into a release, and was reported by Pete Wyckoff <pw@osc.edu>.

Signed-off-by: Roland Dreier <rolandd@cisco.com>
This commit is contained in:
Roland Dreier 2007-06-21 11:05:58 -07:00
parent d025d7858f
commit 24bce50803
1 changed files with 8 additions and 6 deletions
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14
drivers/infiniband/core/umem.c
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@ -225,13 +225,15 @@ void ib_umem_release(struct ib_umem *umem)
* up here and not be able to take the mmap_sem. In that case
* we defer the vm_locked accounting to the system workqueue.
*/
if (context->closing && !down_write_trylock(&mm->mmap_sem)) {
INIT_WORK(&umem->work, ib_umem_account);
umem->mm = mm;
umem->diff = diff;
if (context->closing) {
if (!down_write_trylock(&mm->mmap_sem)) {
INIT_WORK(&umem->work, ib_umem_account);
umem->mm = mm;
umem->diff = diff;
schedule_work(&umem->work);
return;
schedule_work(&umem->work);
return;
}
} else
down_write(&mm->mmap_sem);