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From: Mathieu Desnoyers <compudj@krystal.dyndns.org>
To: Andrew Morton <akpm@osdl.org>
Cc: Greg Kroah-Hartman <gregkh@suse.de>,
Richard J Moore <richardj_moore@uk.ibm.com>,
linux-kernel@vger.kernel.org,
"Martin J. Bligh" <mbligh@mbligh.org>,
Christoph Hellwig <hch@infradead.org>,
Douglas Niehaus <niehaus@eecs.ku.edu>,
Ingo Molnar <mingo@redhat.com>,
ltt-dev@shafik.org, systemtap@sources.redhat.com,
Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH] order of lockdep off/on in vprintk() should be changed
Date: Wed, 24 Jan 2007 12:24:45 -0500 [thread overview]
Message-ID: <20070124172445.GA1145@Krystal> (raw)
In-Reply-To: <20070124165150.GC4979@Krystal>
The order of locking between lockdep_off/on() and local_irq_save/restore() in
vprintk() should be changed.
* In kernel/printk.c :
vprintk() does :
preempt_disable()
local_irq_save()
lockdep_off()
spin_lock(&logbuf_lock)
spin_unlock(&logbuf_lock)
if(!down_trylock(&console_sem))
up(&console_sem)
lockdep_on()
local_irq_restore()
preempt_enable()
The goals here is to make sure we do not call printk() recursively from
kernel/lockdep.c:__lock_acquire() (called from spin_* and down/up) nor from
kernel/lockdep.c:trace_hardirqs_on/off() (called from local_irq_restore/save).
It can then potentially call printk() through mark_held_locks/mark_lock.
It correctly protects against the spin_lock call and the up/down call, but it
does not protect against local_irq_restore. It could cause infinite recursive
printk/trace_hardirqs_on() calls when printk() is called from the
mark_lock() error handing path.
We should change the locking so it becomes correct :
preempt_disable()
lockdep_off()
local_irq_save()
spin_lock(&logbuf_lock)
spin_unlock(&logbuf_lock)
if(!down_trylock(&console_sem))
up(&console_sem)
local_irq_restore()
lockdep_on()
preempt_enable()
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -530,8 +530,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
zap_locks();
/* This stops the holder of console_sem just where we want him */
- local_irq_save(flags);
lockdep_off();
+ local_irq_save(flags);
spin_lock(&logbuf_lock);
printk_cpu = smp_processor_id();
@@ -640,8 +640,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
console_locked = 0;
up(&console_sem);
}
- lockdep_on();
local_irq_restore(flags);
+ lockdep_on();
} else {
/*
* Someone else owns the drivers. We drop the spinlock, which
@@ -650,8 +650,8 @@ asmlinkage int vprintk(const char *fmt, va_list args)
*/
printk_cpu = UINT_MAX;
spin_unlock(&logbuf_lock);
- lockdep_on();
local_irq_restore(flags);
+ lockdep_on();
}
preempt_enable();
--
OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
next prev parent reply other threads:[~2007-01-24 17:24 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-20 23:52 [PATCH 0/4] Linux Kernel Markers Mathieu Desnoyers
2006-12-20 23:57 ` [PATCH 1/4] Linux Kernel Markers : Architecture agnostic code Mathieu Desnoyers
2006-12-20 23:59 ` [PATCH 2/4] Linux Kernel Markers : kconfig menus Mathieu Desnoyers
2006-12-21 0:00 ` [PATCH 3/4] Linux Kernel Markers : i386 optimisation Mathieu Desnoyers
2006-12-21 0:01 ` [PATCH 4/4] Linux Kernel Markers : powerpc optimisation Mathieu Desnoyers
2007-01-13 1:33 ` [PATCH 0/4] Linux Kernel Markers Richard J Moore
2007-01-13 5:45 ` Mathieu Desnoyers
2007-01-16 17:41 ` [PATCH 0/4 update] Linux Kernel Markers - i386 : pIII erratum 49 : XMC Mathieu Desnoyers
2007-01-16 18:35 ` Frank Ch. Eigler
2007-01-16 21:27 ` [PATCH 0/4 update] kprobes and traps Mathieu Desnoyers
2007-01-17 12:25 ` S. P. Prasanna
2007-01-16 17:56 ` [PATCH 1/2] lockdep missing barrier() Mathieu Desnoyers
2007-01-24 4:26 ` Andrew Morton
2007-01-24 16:51 ` Mathieu Desnoyers
2007-01-24 17:24 ` Mathieu Desnoyers [this message]
2007-01-24 17:55 ` [PATCH] minimize lockdep_on/off side-effect Mathieu Desnoyers
2007-01-16 17:56 ` [PATCH 2/2] lockdep reentrancy Mathieu Desnoyers
2007-01-24 4:29 ` Andrew Morton
2007-01-24 16:55 ` Mathieu Desnoyers
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