Messages in this thread | | | Date | Thu, 17 Jun 2021 23:12:46 +0800 | From | Boqun Feng <> | Subject | Re: [PATCH 3/3] locking/lockdep: print possible warning after counting deps |
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Hi,
On Thu, Jun 17, 2021 at 10:28:28PM +0800, Xiongwei Song wrote: > From: Xiongwei Song <sxwjean@gmail.com> > > 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 <longman@redhat.com> > Signed-off-by: Xiongwei Song <sxwjean@gmail.com> > --- > 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 >
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