• Trond Myklebust's avatar
    namei: results of d_is_negative() should be checked after dentry revalidation · daf3761c
    Trond Myklebust authored
    Leandro Awa writes:
     "After switching to version 4.1.6, our parallelized and distributed
      workflows now fail consistently with errors of the form:
    
      T34: ./regex.c:39:22: error: config.h: No such file or directory
    
      From our 'git bisect' testing, the following commit appears to be the
      possible cause of the behavior we've been seeing: commit 766c4cbf"
    
    Al Viro says:
     "What happens is that 766c4cbf got the things subtly wrong.
    
      We used to treat d_is_negative() after lookup_fast() as "fall with
      ENOENT".  That was wrong - checking ->d_flags outside of ->d_seq
      protection is unreliable and failing with hard error on what should've
      fallen back to non-RCU pathname resolution is a bug.
    
      Unfortunately, we'd pulled the test too far up and ran afoul of
      another kind of staleness.  The dentry might have been absolutely
      stable from the RCU point of view (and we might be on UP, etc), but
      stale from the remote fs point of view.  If ->d_revalidate() returns
      "it's actually stale", dentry gets thrown away and the original code
      wouldn't even have looked at its ->d_flags.
    
      What we need is to check ->d_flags where 766c4cbf does (prior to
      ->d_seq validation) but only use the result in cases where we do not
      discard this dentry outright"
    Reported-by: default avatarLeandro Awa <lawa@nvidia.com>
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=104911
    Fixes: 766c4cbf ("namei: d_is_negative() should be checked...")
    Tested-by: default avatarLeandro Awa <lawa@nvidia.com>
    Cc: stable@vger.kernel.org # v4.1+
    Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
    Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    daf3761c
namei.c 115 KB