Commit c1530019 authored Apr 15, 2011 by Tim Chen Committed by Linus Torvalds Apr 15, 2011

vfs: Fix absolute RCU path walk failures due to uninitialized seq number



During RCU walk in path_lookupat and path_openat, the rcu lookup
frequently failed if looking up an absolute path, because when root
directory was looked up, seq number was not properly set in nameidata.

We dropped out of RCU walk in nameidata_drop_rcu due to mismatch in
directory entry's seq number.  We reverted to slow path walk that need
to take references.

With the following patch, I saw a 50% increase in an exim mail server
benchmark throughput on a 4-socket Nehalem-EX system.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: stable@kernel.org (v2.6.38)
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 5853b4f0

fs/namei.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -697,6 +697,7 @@ static __always_inline void set_root_rcu(struct nameidata *nd)
		do {
		seq = read_seqcount_begin(&fs->seq);
		nd->root = fs->root;
		nd->seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
		} while (read_seqcount_retry(&fs->seq, seq));
		}
		}

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