• Zach Brown's avatar
    dio: fix cache invalidation after sync writes · bdb76ef5
    Zach Brown authored
    Commit commit 65b8291c ("dio: invalidate
    clean pages before dio write") introduced a bug which stopped dio from
    ever invalidating the page cache after writes.  It still invalidated it
    before writes so most users were fine.
    
    Karl Schendel reported ( http://lkml.org/lkml/2007/10/26/481 ) hitting
    this bug when he had a buffered reader immediately reading file data
    after an O_DIRECT wirter had written the data.  The kernel issued
    read-ahead beyond the position of the reader which overlapped with the
    O_DIRECT writer.  The failure to invalidate after writes caused the
    reader to see stale data from the read-ahead.
    
    The following patch is originally from Karl.  The following commentary
    is his:
    
    	The below 3rd try takes on your suggestion of just invalidating
    	no matter what the retval from the direct_IO call.  I ran it
    	thru the test-case several times and it has worked every time.
    	The post-invalidate is probably still too early for async-directio,
    	but I don't have a testcase for that;  just sync.  And, this
    	won't be any worse in the async case.
    
    I added a test to the aio-dio-regress repository which mimics Karl's IO
    pattern.  It verifed the bad behaviour and that the patch fixed it.  I
    agree with Karl, this still doesn't help the case where a buffered
    reader follows an AIO O_DIRECT writer.  That will require a bit more
    work.
    
    This gives up on the idea of returning EIO to indicate to userspace that
    stale data remains if the invalidation failed.
    Signed-off-by: default avatarZach Brown <zach.brown@oracle.com>
    Cc: Karl Schendel <kschendel@datallegro.com>
    Cc: Benjamin LaHaise <bcrl@kvack.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Cc: Leonid Ananiev <leonid.i.ananiev@linux.intel.com>
    Cc: Chris Mason <chris.mason@oracle.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    bdb76ef5
filemap.c 67.6 KB