| Message ID | 20190325123252.10211-1-jlayton@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] locks: wake any locks blocked on request before deadlock check | expand |
On Mon, Mar 25, 2019 at 08:32:52AM -0400, Jeff Layton wrote: > Andreas reported that he was seeing the tdbtorture test fail in some > cases with -EDEADLCK when it wasn't before. Some debugging showed that > deadlock detection was sometimes discovering the caller's lock request > itself in a dependency chain. > > While we remove the request from the blocked_lock_hash prior to > reattempting to acquire it, any locks that are blocked on that request > will still be present in the hash and will still have their fl_blocker > pointer set to the current request. This description is a lot easier for me to follow, thanks! > This causes posix_locks_deadlock to find a deadlock dependency chain > when it shouldn't, as a lock request cannot block itself. > > We are going to end up waking all of those blocked locks anyway when we > go to reinsert the request back into the blocked_lock_hash, so just do > it prior to checking for deadlocks. This ensures that any lock blocked > on the current request will no longer be part of any blocked request > chain. Looks right to me. --b. > > URL: https://bugzilla.kernel.org/show_bug.cgi?id=202975 > Fixes: 5946c4319ebb ("fs/locks: allow a lock request to block other requests.") > Cc: stable@vger.kernel.org > Reported-by: Andreas Schneider <asn@redhat.com> > Signed-off-by: Neil Brown <neilb@suse.com> > Signed-off-by: Jeff Layton <jlayton@kernel.org> > --- > fs/locks.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/fs/locks.c b/fs/locks.c > index eaa1cfaf73b0..71d0c6c2aac5 100644 > --- a/fs/locks.c > +++ b/fs/locks.c > @@ -1160,6 +1160,11 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request, > */ > error = -EDEADLK; > spin_lock(&blocked_lock_lock); > + /* > + * Ensure that we don't find any locks blocked on this > + * request during deadlock detection. > + */ > + __locks_wake_up_blocks(request); > if (likely(!posix_locks_deadlock(request, fl))) { > error = FILE_LOCK_DEFERRED; > __locks_insert_block(fl, request, > -- > 2.20.1
On Mon, Mar 25 2019, Jeff Layton wrote: > Andreas reported that he was seeing the tdbtorture test fail in some > cases with -EDEADLCK when it wasn't before. Some debugging showed that > deadlock detection was sometimes discovering the caller's lock request > itself in a dependency chain. > > While we remove the request from the blocked_lock_hash prior to > reattempting to acquire it, any locks that are blocked on that request > will still be present in the hash and will still have their fl_blocker > pointer set to the current request. > > This causes posix_locks_deadlock to find a deadlock dependency chain > when it shouldn't, as a lock request cannot block itself. > > We are going to end up waking all of those blocked locks anyway when we > go to reinsert the request back into the blocked_lock_hash, so just do > it prior to checking for deadlocks. This ensures that any lock blocked > on the current request will no longer be part of any blocked request > chain. > > URL: https://bugzilla.kernel.org/show_bug.cgi?id=202975 > Fixes: 5946c4319ebb ("fs/locks: allow a lock request to block other requests.") > Cc: stable@vger.kernel.org > Reported-by: Andreas Schneider <asn@redhat.com> > Signed-off-by: Neil Brown <neilb@suse.com> > Signed-off-by: Jeff Layton <jlayton@kernel.org> Yes, I'm happy with this patch and description. It is more "obviously correct" than the other patch. Thanks, NeilBrown > --- > fs/locks.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/fs/locks.c b/fs/locks.c > index eaa1cfaf73b0..71d0c6c2aac5 100644 > --- a/fs/locks.c > +++ b/fs/locks.c > @@ -1160,6 +1160,11 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request, > */ > error = -EDEADLK; > spin_lock(&blocked_lock_lock); > + /* > + * Ensure that we don't find any locks blocked on this > + * request during deadlock detection. > + */ > + __locks_wake_up_blocks(request); > if (likely(!posix_locks_deadlock(request, fl))) { > error = FILE_LOCK_DEFERRED; > __locks_insert_block(fl, request, > -- > 2.20.1
diff --git a/fs/locks.c b/fs/locks.c index eaa1cfaf73b0..71d0c6c2aac5 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -1160,6 +1160,11 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request, */ error = -EDEADLK; spin_lock(&blocked_lock_lock); + /* + * Ensure that we don't find any locks blocked on this + * request during deadlock detection. + */ + __locks_wake_up_blocks(request); if (likely(!posix_locks_deadlock(request, fl))) { error = FILE_LOCK_DEFERRED; __locks_insert_block(fl, request,
Andreas reported that he was seeing the tdbtorture test fail in some cases with -EDEADLCK when it wasn't before. Some debugging showed that deadlock detection was sometimes discovering the caller's lock request itself in a dependency chain. While we remove the request from the blocked_lock_hash prior to reattempting to acquire it, any locks that are blocked on that request will still be present in the hash and will still have their fl_blocker pointer set to the current request. This causes posix_locks_deadlock to find a deadlock dependency chain when it shouldn't, as a lock request cannot block itself. We are going to end up waking all of those blocked locks anyway when we go to reinsert the request back into the blocked_lock_hash, so just do it prior to checking for deadlocks. This ensures that any lock blocked on the current request will no longer be part of any blocked request chain. URL: https://bugzilla.kernel.org/show_bug.cgi?id=202975 Fixes: 5946c4319ebb ("fs/locks: allow a lock request to block other requests.") Cc: stable@vger.kernel.org Reported-by: Andreas Schneider <asn@redhat.com> Signed-off-by: Neil Brown <neilb@suse.com> Signed-off-by: Jeff Layton <jlayton@kernel.org> --- fs/locks.c | 5 +++++ 1 file changed, 5 insertions(+)