| Message ID | 1373547244-5048-1-git-send-email-pshilovsky@samba.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 11 Jul 2013 16:54:04 +0400 Pavel Shilovsky <pshilovsky@samba.org> wrote: > If we request reading or writing on a file that needs to be > reopened, it causes the deadlock: we are already holding rw > semaphore for reading and then we try to acquire it for writing > in cifs_relock_file. Fix this by acquiring the semaphore for > reading in cifs_relock_file due to we don't make any changes in > locks and don't need a write access. > > Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org> > --- > fs/cifs/file.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c > index b149ae4..be24f09 100644 > --- a/fs/cifs/file.c > +++ b/fs/cifs/file.c > @@ -561,11 +561,10 @@ cifs_relock_file(struct cifsFileInfo *cfile) > struct cifs_tcon *tcon = tlink_tcon(cfile->tlink); > int rc = 0; > > - /* we are going to update can_cache_brlcks here - need a write access */ > - down_write(&cinode->lock_sem); > + down_read(&cinode->lock_sem); > if (cinode->can_cache_brlcks) { > - /* can cache locks - no need to push them */ > - up_write(&cinode->lock_sem); > + /* can cache locks - no need to relock */ > + up_read(&cinode->lock_sem); > return rc; > } > > @@ -576,7 +575,7 @@ cifs_relock_file(struct cifsFileInfo *cfile) > else > rc = tcon->ses->server->ops->push_mand_locks(cfile); > > - up_write(&cinode->lock_sem); > + up_read(&cinode->lock_sem); > return rc; > } > Ok, I think this will work, but I'm a little leery of recursively taking the same semaphore twice for read. This really could use a rethink as getting this locking wrong is a great source of subtle bugs. Maybe you could consider using RCU instead? Acked-by: Jeff Layton <jlayton@redhat.com> -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/cifs/file.c b/fs/cifs/file.c index b149ae4..be24f09 100644 --- a/fs/cifs/file.c +++ b/fs/cifs/file.c @@ -561,11 +561,10 @@ cifs_relock_file(struct cifsFileInfo *cfile) struct cifs_tcon *tcon = tlink_tcon(cfile->tlink); int rc = 0; - /* we are going to update can_cache_brlcks here - need a write access */ - down_write(&cinode->lock_sem); + down_read(&cinode->lock_sem); if (cinode->can_cache_brlcks) { - /* can cache locks - no need to push them */ - up_write(&cinode->lock_sem); + /* can cache locks - no need to relock */ + up_read(&cinode->lock_sem); return rc; } @@ -576,7 +575,7 @@ cifs_relock_file(struct cifsFileInfo *cfile) else rc = tcon->ses->server->ops->push_mand_locks(cfile); - up_write(&cinode->lock_sem); + up_read(&cinode->lock_sem); return rc; }
If we request reading or writing on a file that needs to be reopened, it causes the deadlock: we are already holding rw semaphore for reading and then we try to acquire it for writing in cifs_relock_file. Fix this by acquiring the semaphore for reading in cifs_relock_file due to we don't make any changes in locks and don't need a write access. Signed-off-by: Pavel Shilovsky <pshilovsky@samba.org> --- fs/cifs/file.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)