Hi,
On Thu, Jun 17, 2021 at 10:28:28PM +0800, Xiongwei Song wrote:
> From: Xiongwei Song <[email protected]>
>
> The graph walk might hit error when counting dependencies. Once the
> return value is negative, print a warning to reminder users.
>
Thanks for the improvement, but please see below:
> Suggested-by: Waiman Long <[email protected]>
> Signed-off-by: Xiongwei Song <[email protected]>
> ---
> kernel/locking/lockdep.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index cb94097014d8..cfe0f4374594 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -2028,8 +2028,12 @@ static unsigned long __lockdep_count_forward_deps(struct lock_list *this)
> {
> unsigned long count = 0;
> struct lock_list *target_entry;
> + enum bfs_result ret;
> +
> + ret = __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
>
> - __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
> + if (bfs_error(ret))
> + print_bfs_bug(ret);
Here print_bfs_bug() will eventually call debug_locks_off_graph_unlock()
to release the graph lock, and the caller (lockdep_count_fowards_deps())
will also call graph_unlock() afterwards, and that means we unlock
*twice* if a BFS error happens... although in that case, lockdep should
stop working so messing up with the graph lock may not hurt anything,
but still, I don't think we want to do that.
So probably you can open-code __lockdep_count_forward_deps() into
lockdep_count_forwards_deps(), and call print_bfs_bug() or
graph_unlock() accordingly. The body of __lockdep_count_forward_deps()
is really small, so I think it's OK to open-code it into its caller.
Regards,
Boqun
>
> return count;
> }
> @@ -2053,8 +2057,12 @@ static unsigned long __lockdep_count_backward_deps(struct lock_list *this)
> {
> unsigned long count = 0;
> struct lock_list *target_entry;
> + enum bfs_result ret;
> +
> + ret = __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
>
> - __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
> + if (bfs_error(ret))
> + print_bfs_bug(ret);
>
> return count;
> }
> --
> 2.30.2
>
On Thu, Jun 17, 2021 at 11:13 PM Boqun Feng <[email protected]> wrote:
>
> Hi,
>
> On Thu, Jun 17, 2021 at 10:28:28PM +0800, Xiongwei Song wrote:
> > From: Xiongwei Song <[email protected]>
> >
> > The graph walk might hit error when counting dependencies. Once the
> > return value is negative, print a warning to reminder users.
> >
>
> Thanks for the improvement, but please see below:
>
> > Suggested-by: Waiman Long <[email protected]>
> > Signed-off-by: Xiongwei Song <[email protected]>
> > ---
> > kernel/locking/lockdep.c | 12 ++++++++++--
> > 1 file changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> > index cb94097014d8..cfe0f4374594 100644
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -2028,8 +2028,12 @@ static unsigned long __lockdep_count_forward_deps(struct lock_list *this)
> > {
> > unsigned long count = 0;
> > struct lock_list *target_entry;
> > + enum bfs_result ret;
> > +
> > + ret = __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
> >
> > - __bfs_forwards(this, (void *)&count, noop_count, NULL, &target_entry);
> > + if (bfs_error(ret))
> > + print_bfs_bug(ret);
>
> Here print_bfs_bug() will eventually call debug_locks_off_graph_unlock()
> to release the graph lock, and the caller (lockdep_count_fowards_deps())
> will also call graph_unlock() afterwards, and that means we unlock
> *twice* if a BFS error happens... although in that case, lockdep should
> stop working so messing up with the graph lock may not hurt anything,
> but still, I don't think we want to do that.
>
> So probably you can open-code __lockdep_count_forward_deps() into
> lockdep_count_forwards_deps(), and call print_bfs_bug() or
> graph_unlock() accordingly. The body of __lockdep_count_forward_deps()
> is really small, so I think it's OK to open-code it into its caller.
Thank you so much for the detailed comments. Let me improve and update
the patch.
Regards,
Xiongwei
>
> Regards,
> Boqun
>
> >
> > return count;
> > }
> > @@ -2053,8 +2057,12 @@ static unsigned long __lockdep_count_backward_deps(struct lock_list *this)
> > {
> > unsigned long count = 0;
> > struct lock_list *target_entry;
> > + enum bfs_result ret;
> > +
> > + ret = __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
> >
> > - __bfs_backwards(this, (void *)&count, noop_count, NULL, &target_entry);
> > + if (bfs_error(ret))
> > + print_bfs_bug(ret);
> >
> > return count;
> > }
> > --
> > 2.30.2
> >