On Tue, Sep 19, 2017 at 12:52:06PM +0000, Boqun Feng wrote:
> For a potential deadlock about CROSSRELEASE as follow:
>
> P1 P2
> =========== =============
> lock(A)
> lock(X)
> lock(A)
> commit(X)
>
> A: normal lock, X: cross lock
>
> , we could detect it at two places:
>
> 1. commit time:
>
> We have run P1 first, and have dependency A --> X in graph, and
> then we run P2, and find the deadlock.
>
> 2. acquisition time:
>
> We have run P2 first, and have dependency X --> A, in
> graph(because another P3 may run previously and is acquiring for
> lock X), and then we run P1 and find the deadlock.
>
> In current print_circular_lock_scenario(), for 1) we could print the
> right scenario and note that's a deadlock related to CROSSRELEASE,
> however for 2) we print the scenario as a normal lockdep deadlock,
> instead we print something like:
>
> | [ 35.310179] ======================================================
> | [ 35.310749] WARNING: possible circular locking dependency detected
> | [ 35.310749] 4.13.0-rc4+ #1 Not tainted
> | [ 35.310749] ------------------------------------------------------
> | [ 35.310749] torture_onoff/766 is trying to acquire lock:
> | [ 35.313943] ((complete)&st->done){+.+.}, at: [<ffffffffb905f5a6>]
> takedown_cpu+0x86/0xf0
> | [ 35.313943]
> | [ 35.313943] but task is already holding lock:
> | [ 35.313943] (sparse_irq_lock){+.+.}, at: [<ffffffffb90c5e42>]
> irq_lock_sparse+0x12/0x20
> | [ 35.313943]
> | [ 35.313943] which lock already depends on the new lock.
> ...
> | [ 35.313943] other info that might help us debug this:
> | [ 35.313943]
> | [ 35.313943] Possible unsafe locking scenario:
> | [ 35.313943]
> | [ 35.313943] CPU0 CPU1
> | [ 35.313943] ---- ----
> | [ 35.313943] lock(sparse_irq_lock);
> | [ 35.313943] lock((complete)&st->done);
> | [ 35.313943] lock(sparse_irq_lock);
> | [ 35.313943] lock((complete)&st->done);
> | [ 35.313943]
> | [ 35.313943] *** DEADLOCK ***
>
> It's better to print a proper scenario related to CROSSRELEASE to help
> users find their bugs more easily, so improve this.
> Hi Byungchul, Any idea on this one? Regards, Boqun > Cc: "Paul E. McKenney" <[email protected]> > Cc: Byungchul Park <[email protected]> > Cc: Steven Rostedt <[email protected]> > Signed-off-by: Boqun Feng <[email protected]> > --- > The sample of print_circular_lock_scenario() is from Paul Mckenney. > > kernel/locking/lockdep.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 44c8d0d17170..67a407bcc814 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1156,6 +1156,23 @@ print_circular_lock_scenario(struct held_lock *src, > __print_lock_name(target); > printk(KERN_CONT ");\n"); > printk("\n *** DEADLOCK ***\n\n"); > + } else if (cross_lock(src->instance)) { > + printk(" Possible unsafe locking scenario by crosslock:\n\n"); > + printk(" CPU0 CPU1\n"); > + printk(" ---- ----\n"); > + printk(" lock("); > + __print_lock_name(target); > + printk(KERN_CONT ");\n"); > + printk(" lock("); > + __print_lock_name(source); > + printk(KERN_CONT ");\n"); > + printk(" lock("); > + __print_lock_name(parent == source ? target : parent); > + printk(KERN_CONT ");\n"); > + printk(" unlock("); > + __print_lock_name(source); > + printk(KERN_CONT ");\n"); > + printk("\n *** DEADLOCK ***\n\n"); > } else { > printk(" Possible unsafe locking scenario:\n\n"); > printk(" CPU0 CPU1\n"); > -- > 2.14.1 >
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