Re: [PATCH] nfsd: fix handling of cached open files in nfsd4_open codepath

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2023-01-06 at 17:56 +0000, Chuck Lever III wrote:
> 
> > On Jan 5, 2023, at 2:55 PM, Jeff Layton <jlayton@kernel.org> wrote:
> > 
> > Commit fb70bf124b05 ("NFSD: Instantiate a struct file when creating a
> > regular NFSv4 file") added the ability to cache an open fd over a
> > compound. There are a couple of problems with the way this currently
> > works:
> > 
> > It's racy, as a newly-created nfsd_file can end up with its PENDING bit
> > cleared while the nf is hashed, and the nf_file pointer is still zeroed
> > out. Other tasks can find it in this state and they expect to see a
> > valid nf_file, and can oops if nf_file is NULL.
> > 
> > Also, there is no guarantee that we'll end up creating a new nfsd_file
> > if one is already in the hash. If an extant entry is in the hash with a
> > valid nf_file, nfs4_get_vfs_file will clobber its nf_file pointer with
> > the value of op_file and the old nf_file will leak.
> > 
> > Fix both issues by making a new nfsd_file_acquirei_opened variant that
> > takes an optional file pointer. If one is present when this is called,
> > we'll take a new reference to it instead of trying to open the file. If
> > the nfsd_file already has a valid nf_file, we'll just ignore the
> > optional file and pass the nfsd_file back as-is.
> > 
> > Also rework the tracepoints a bit to allow for an "opened" variant and
> > don't try to avoid counting acquisitions in the case where we already
> > have a cached open file.
> > 
> > Fixes: fb70bf124b05 ("NFSD: Instantiate a struct file when creating a regular NFSv4 file")
> > Cc: Trond Myklebust <trondmy@hammerspace.com>
> > Reported-by: Stanislav Saner <ssaner@redhat.com>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> > fs/nfsd/filecache.c | 40 ++++++++++++++++++----------------
> > fs/nfsd/filecache.h |  5 +++--
> > fs/nfsd/nfs4state.c | 16 ++++----------
> > fs/nfsd/trace.h     | 52 ++++++++++++---------------------------------
> > 4 files changed, 42 insertions(+), 71 deletions(-)
> > 
> > v3: add new nfsd_file_acquire_opened variant instead of changing
> >    nfsd_file_acquire prototype
> 
> Hi Jeff, v3 applied to nfsd's for-rc.
> 

Can you also add:

    Reported-and-Tested-by: Ruben Vestergaard    rubenv@drcmr.dk
    Reported-and-Tested-by: Torkil Svensgaard    torkil@drcmr.dk

They've been helping test these patches (albeit backported versions on a
RHEL9 kernel), and reported the crash that helped me track this down.

Many thanks!
-- 
Jeff Layton <jlayton@kernel.org>