[linux-cifs] Re: [PATCH] Complete oplock break jobs before closing file handle


On Mon, 2015-01-19 at 07:02 -0500, Jeff Layton wrote:
> On Sat, 17 Jan 2015 07:45:13 -0600
> Shirish Pargaonkar  wrote:
> 
> > On Thu, Jan 15, 2015 at 6:22 AM, Sachin Prabhu  wrote:
> > > Commit
> > > c11f1df5003d534fd067f0168bfad7befffb3b5c
> > > requires writers to wait for any pending oplock break handler to
> > > complete before proceeding to write. This is done by waiting on bit
> > > CIFS_INODE_PENDING_OPLOCK_BREAK in cifsFileInfo->flags. This bit is
> > > cleared by the oplock break handler job queued on the workqueue once it
> > > has completed handling the oplock break allowing writers to proceed with
> > > writing to the file.
> > >
> > > While testing, it was noticed that the filehandle could be closed while
> > > there is a pending oplock break which results in the oplock break
> > > handler on the cifsiod workqueue being cancelled before it has had a
> > > chance to execute and clear the CIFS_INODE_PENDING_OPLOCK_BREAK bit.
> > > Any subsequent attempt to write to this file hangs waiting for the
> > > CIFS_INODE_PENDING_OPLOCK_BREAK bit to be cleared.
> > >
> > > We fix this by ensuring that we also clear the bit
> > > CIFS_INODE_PENDING_OPLOCK_BREAK when we remove the oplock break handler
> > > from the workqueue.
> > >
> > > The bug was found by Red Hat QA while testing using ltp's fsstress
> > > command.
> > >
> > > Signed-off-by: Sachin Prabhu 
> > > Signed-off-by: Jeff Layton 
> > > ---
> > >  fs/cifs/file.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> > > index 96b7e9b..74f1287 100644
> > > --- a/fs/cifs/file.c
> > > +++ b/fs/cifs/file.c
> > > @@ -366,6 +366,7 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
> > >         struct cifsLockInfo *li, *tmp;
> > >         struct cifs_fid fid;
> > >         struct cifs_pending_open open;
> > > +       bool oplock_break_cancelled;
> > >
> > >         spin_lock(&cifs_file_list_lock);
> > >         if (--cifs_file->count > 0) {
> > > @@ -397,7 +398,7 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
> > >         }
> > >         spin_unlock(&cifs_file_list_lock);
> > >
> > > -       cancel_work_sync(&cifs_file->oplock_break);
> > > +       oplock_break_cancelled = cancel_work_sync(&cifs_file->oplock_break);
> > >
> > >         if (!tcon->need_reconnect && !cifs_file->invalidHandle) {
> > >                 struct TCP_Server_Info *server = tcon->ses->server;
> > > @@ -409,6 +410,9 @@ void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
> > >                 _free_xid(xid);
> > >         }
> > >
> > > +       if (oplock_break_cancelled)
> > > +               cifs_done_oplock_break(cifsi);
> > > +
> > >         cifs_del_pending_open(&open);
> > >
> > >         /*
> > > --
> > > 2.1.0
> > >
> > > --
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> > 
> > 
> > Does it matter what cancel_work_sync() returns?
> > Should cifs_done_oplock_break(cifsi); be called unconditionally?
> 
> I guess the question is whether you can end up with another oplock
> break racing in between cancel_work_sync and the
> cifs_done_oplock_break. If that can't happen, then calling it
> unconditionally is fine.

By the time we call cancel_work_sync(), we have removed the file from
the list of files opened for the tcon. This is the file list used by
is_valid_oplock_break() to find the file which the oplock break refers
to and to schedule an oplock break work. Since the file is no longer in
the list of open files held for the tcon, we cannot have an oplock break
sneaking in between  cancel_work_sync() and cifs_done_oplock_break(). So
I guess it can be called unconditionally. 

Should I make the change?

> 
> > Also, should this also to go stable?
> 
> Yes, probably. It can cause the client to hang.
> 

Sachin Prabhu



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