From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: akpm@linux-foundation.org, mingo@kernel.org,
linux-kernel@vger.kernel.org, akinobu.mita@gmail.com,
jack@suse.cz, torvalds@linux-foundation.org,
peter@hurleysoftware.com, sergey.senozhatsky@gmail.com,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code
Date: Fri, 29 Jan 2016 00:42:57 +0900 [thread overview]
Message-ID: <20160128154257.GA564@swordfish> (raw)
In-Reply-To: <20160128105342.GB610@swordfish>
On (01/28/16 19:53), Sergey Senozhatsky wrote:
> > ah... silly me... you mean the first CPU that triggers the spin_dump() will
> ^^^ this, of course, is true for
> console_sem->lock and logbuf_lock
> only.
>
> > deadlock itself, so the rest of CPUs will see endless recursive
> > spin_lock()->spin_dump()->spin_lock()->spin_dump() calls?
[..]
> > Can you please update your bug description in the commit message?
> > It's the deadlock that is causing the recursion on other CPUs in the
> > first place.
no, don't update anything. I was completely wrong. it's not a deadlock
that is the root cause here.
even if at some level of recursion (nested printk calls)
spin_dump()->__spin_lock_debug()->arch_spin_trylock() acquires the
lock, it returns back with the spin lock unlocked anyway.
vprintk_emit()
console_trylock()
spin_lock()
spin_dump()
vprintk_emit()
console_trylock()
spin_lock()
spin_dump()
vprintk_emit()
console_trylock()
spin_lock() << OK, got the lock finally
sem->count--
spin_unlock() << unlock, return
arch_spin_lock() << got the lock, return
sem->count--
spin_unlock() << unlock, return
arch_spin_lock() << got the lock, return
sem->count--
spin_unlock() << unlock, return
...um
> But I found there's a possiblity in the debug code *itself* to cause a
> lockup.
please explain.
-ss
next prev parent reply other threads:[~2016-01-28 15:44 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-27 12:01 [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park
2016-01-27 22:49 ` Peter Hurley
2016-01-28 7:15 ` Byungchul Park
2016-01-29 8:19 ` Byungchul Park
2016-01-28 1:42 ` Byungchul Park
2016-01-28 2:37 ` Sergey Senozhatsky
2016-01-28 4:36 ` byungchul.park
2016-01-28 6:05 ` Sergey Senozhatsky
2016-01-28 8:13 ` Byungchul Park
2016-01-28 10:41 ` Sergey Senozhatsky
2016-01-28 10:53 ` Sergey Senozhatsky
2016-01-28 15:42 ` Sergey Senozhatsky [this message]
2016-01-28 23:08 ` Peter Hurley
2016-01-28 23:54 ` Byungchul Park
2016-01-29 0:54 ` Sergey Senozhatsky
2016-01-29 3:00 ` Byungchul Park
2016-01-29 4:05 ` Sergey Senozhatsky
2016-01-29 12:15 ` Byungchul Park
2016-01-29 0:27 ` Sergey Senozhatsky
2016-01-29 4:32 ` Peter Hurley
2016-01-29 5:28 ` Sergey Senozhatsky
2016-01-29 5:48 ` Peter Hurley
2016-01-29 6:16 ` Sergey Senozhatsky
2016-01-29 6:37 ` Sergey Senozhatsky
2016-01-31 12:30 ` Sergey Senozhatsky
2016-01-31 12:33 ` [PATCH 1/3] printk: introduce console_reset_on_panic() function Sergey Senozhatsky
2016-01-31 12:33 ` [PATCH 2/3] printk: introduce reset_console_drivers() Sergey Senozhatsky
2016-01-31 12:47 ` kbuild test robot
2016-01-31 12:33 ` [PATCH 3/3] spinlock_debug: panic on recursive lock spin_dump() Sergey Senozhatsky
2016-02-01 16:14 ` Sergey Senozhatsky
2016-02-02 7:59 ` Sergey Senozhatsky
2016-01-31 12:42 ` [PATCH 1/3] printk: introduce console_reset_on_panic() function kbuild test robot
2016-01-29 6:54 ` [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park
2016-01-29 7:13 ` Sergey Senozhatsky
2016-01-29 8:13 ` Byungchul Park
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