Messages in this thread | | | From | Xiongwei Song <> | Date | Fri, 18 Jun 2021 09:54:59 +0800 | Subject | Re: [PATCH 3/3] locking/lockdep: print possible warning after counting deps |
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On Thu, Jun 17, 2021 at 11:13 PM Boqun Feng <boqun.feng@gmail.com> wrote: > > 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.
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 > >
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