From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
linux-mm@kvack.org, iommu@lists.linux-foundation.org,
Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Tejun Heo <tj@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2 07/17] debugobjects: Move printk out of db lock critical sections
Date: Thu, 22 Nov 2018 11:04:22 +0900 [thread overview]
Message-ID: <20181122020422.GA3441@jagdpanzerIV> (raw)
In-Reply-To: <2ddd9e3d-951e-1892-c941-54be80f7e6aa@redhat.com>
On (11/21/18 11:49), Waiman Long wrote:
[..]
> > case ODEBUG_STATE_ACTIVE:
> > - debug_print_object(obj, "init");
> > state = obj->state;
> > raw_spin_unlock_irqrestore(&db->lock, flags);
> > + debug_print_object(obj, "init");
> > debug_object_fixup(descr->fixup_init, addr, state);
> > return;
> >
> > case ODEBUG_STATE_DESTROYED:
> > - debug_print_object(obj, "init");
> > + debug_printobj = true;
> > break;
> > default:
> > break;
> > }
> >
> > raw_spin_unlock_irqrestore(&db->lock, flags);
> > + if (debug_chkstack)
> > + debug_object_is_on_stack(addr, onstack);
> > + if (debug_printobj)
> > + debug_print_object(obj, "init");
> >
[..]
>
> As a side note, one of the test systems that I used generated a
> debugobjects splat in the bootup process and the system hanged
> afterward. Applying this patch alone fix the hanging problem and the
> system booted up successfully. So it is not really a good idea to call
> printk() while holding a raw spinlock.
Right, I like this patch.
And I think that we, maybe, can go even further.
Some serial consoles call mod_timer(). So what we could have with the
debug objects enabled was
mod_timer()
lock_timer_base()
debug_activate()
printk()
call_console_drivers()
foo_console()
mod_timer()
lock_timer_base() << deadlock
That's one possible scenario. The other one can involve console's
IRQ handler, uart port spinlock, mod_timer, debug objects, printk,
and an eventual deadlock on the uart port spinlock. This one can
be mitigated with printk_safe. But mod_timer() deadlock will require
a different fix.
So maybe we need to switch debug objects print-outs to _always_
printk_deferred(). Debug objects can be used in code which cannot
do direct printk() - timekeeping is just one example.
-ss
next prev parent reply other threads:[~2018-11-22 2:04 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 18:55 [PATCH v2 00/17] locking/lockdep: Add a new class of terminal locks Waiman Long
2018-11-19 18:55 ` [PATCH v2 01/17] locking/lockdep: Remove version from lock_class structure Waiman Long
2018-12-11 15:22 ` [tip:locking/core] locking/lockdep: Remove ::version " tip-bot for Waiman Long
2018-11-19 18:55 ` [PATCH v2 02/17] locking/lockdep: Rework lockdep_set_novalidate_class() Waiman Long
2018-11-19 18:55 ` [PATCH v2 03/17] locking/lockdep: Add a new terminal lock type Waiman Long
2018-12-07 9:19 ` Peter Zijlstra
2018-11-19 18:55 ` [PATCH v2 04/17] locking/lockdep: Add DEFINE_TERMINAL_SPINLOCK() and related macros Waiman Long
2018-11-19 18:55 ` [PATCH v2 05/17] printk: Mark logbuf_lock & console_owner_lock as terminal locks Waiman Long
2018-11-19 18:55 ` [PATCH v2 06/17] debugobjects: Mark pool_lock as a terminal lock Waiman Long
2018-11-19 18:55 ` [PATCH v2 07/17] debugobjects: Move printk out of db lock critical sections Waiman Long
2018-11-21 16:49 ` Waiman Long
2018-11-22 2:04 ` Sergey Senozhatsky [this message]
2018-11-22 10:16 ` Peter Zijlstra
2018-11-23 2:40 ` Sergey Senozhatsky
2018-11-23 11:48 ` Petr Mladek
2018-11-26 4:57 ` Sergey Senozhatsky
2018-11-29 13:09 ` Petr Mladek
2018-11-22 16:02 ` Petr Mladek
2018-11-22 20:29 ` Waiman Long
2018-11-23 11:36 ` Petr Mladek
2018-11-22 19:57 ` Waiman Long
2018-11-23 2:35 ` Sergey Senozhatsky
2018-11-23 11:20 ` Petr Mladek
2018-12-07 9:21 ` Peter Zijlstra
2018-11-19 18:55 ` [PATCH v2 08/17] locking/lockdep: Add support for nestable terminal locks Waiman Long
2018-12-07 9:22 ` Peter Zijlstra
2018-12-07 9:52 ` Peter Zijlstra
2018-11-19 18:55 ` [PATCH v2 09/17] debugobjects: Make object hash locks " Waiman Long
2018-11-22 15:33 ` Petr Mladek
2018-11-22 20:17 ` Waiman Long
2018-11-23 9:29 ` Petr Mladek
2018-12-07 9:47 ` Peter Zijlstra
2018-11-19 18:55 ` [PATCH v2 10/17] lib/stackdepot: Make depot_lock a terminal spinlock Waiman Long
2018-11-19 18:55 ` [PATCH v2 11/17] locking/rwsem: Mark rwsem.wait_lock as a terminal lock Waiman Long
2018-11-19 18:55 ` [PATCH v2 12/17] cgroup: Mark the rstat percpu lock as terminal Waiman Long
2018-11-19 18:55 ` [PATCH v2 13/17] mm/kasan: Make quarantine_lock a terminal lock Waiman Long
2018-11-19 18:55 ` [PATCH v2 14/17] dma-debug: Mark free_entries_lock as terminal Waiman Long
2018-11-19 18:55 ` [PATCH v2 15/17] kernfs: Mark kernfs_open_node_lock as terminal lock Waiman Long
2018-11-19 18:55 ` [PATCH v2 16/17] delay_acct: Mark task's delays->lock as terminal spinlock Waiman Long
2018-11-19 18:55 ` [PATCH v2 17/17] locking/lockdep: Check raw/non-raw locking conflicts Waiman Long
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