From: Pavel Emelyanov <xemul@openvz.org>
Date: Thu, 10 Oct 2013 13:12:05 +0000 (+0400)
Subject: fuse: Fix O_DIRECT operations vs cached writeback misorder
X-Git-Tag: v3.15-rc1~94^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ea8cd33390fafc1eca06a26e6a9c7bf1d386526f;p=pandora-kernel.git

fuse: Fix O_DIRECT operations vs cached writeback misorder

The problem is:

1. write cached data to a file
2. read directly from the same file (via another fd)

The 2nd operation may read stale data, i.e. the one that was in a file
before the 1st op. Problem is in how fuse manages writeback.

When direct op occurs the core kernel code calls filemap_write_and_wait
to flush all the cached ops in flight. But fuse acks the writeback right
after the ->writepages callback exits w/o waiting for the real write to
happen. Thus the subsequent direct op proceeds while the real writeback
is still in flight. This is a problem for backends that reorder operation.

Fix this by making the fuse direct IO callback explicitly wait on the
in-flight writeback to finish.

Signed-off-by: Maxim Patlasov <MPatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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