From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Tue, 20 Jul 2010 20:24:34 +0000 (-0700)
Subject: vfs: fix RCU-lockdep false positive due to /proc
X-Git-Tag: v2.6.35-rc6~16
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=844b9a8707f1fcf0482e0c52f44a555e799ccda6;p=pandora-kernel.git

vfs: fix RCU-lockdep false positive due to /proc

If a single-threaded process does a file-descriptor operation, and some
other process accesses that same file descriptor via /proc, the current
rcu_dereference_check_fdtable() can give a false-positive RCU-lockdep
splat due to the reference count being increased by the /proc access after
the reference-count check in fget_light() but before the check in
rcu_dereference_check_fdtable().

This commit prevents this false positive by checking for a single-threaded
process.  To avoid #include hell, this commit uses the wrapper for
thread_group_empty(current) defined by rcu_my_thread_group_empty()
provided in a separate commit.

Located-by: Miles Lane <miles.lane@gmail.com>
Located-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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