From: Roland Dreier <rolandd@cisco.com>
Date: Thu, 21 Jun 2007 18:05:58 +0000 (-0700)
Subject: IB/umem: Fix possible hang on process exit
X-Git-Tag: v2.6.22-rc6~38^2~4
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=24bce5080306bd5255cbda3d6b09a29d5515b470;p=pandora-kernel.git

IB/umem: Fix possible hang on process exit

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>
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