From: Rabin Vincent <rabin@rab.in>
To: Namjae Jeon <linkinjeon@gmail.com>
Cc: fengguang.wu@intel.com, axboe@kernel.dk,
linux-kernel@vger.kernel.org, chanho0207@gmail.com
Subject: Re: [PATCHv2] backing-dev: fix wakeup timer races with bdi_unregister()
Date: Fri, 20 Jan 2012 10:54:11 +0530 [thread overview]
Message-ID: <CAH+eYFBHTXVxdepno4xE-AxyYKqtNQHUvCY55z9_otN+25Y8Hg@mail.gmail.com> (raw)
In-Reply-To: <CAKYAXd8poi6Rs7wyvZHre6qx-_i7eq0SBQAJNKNTYTLC5RQKjA@mail.gmail.com>
On Fri, Jan 20, 2012 at 05:16, Namjae Jeon <linkinjeon@gmail.com> wrote:
>> bdi_debug_unregister(bdi);
>> - device_unregister(bdi->dev);
>> +
>> + spin_lock_bh(&bdi->wb_lock);
>> bdi->dev = NULL;
>> + spin_unlock_bh(&bdi->wb_lock);
> Hi.
> Would you explain me why you add spinlock in here ?
wakeup_timer_fn() does the following, where the
trace_writeback_wake_forker_thread() also accesses bdi->dev.
It does this under the wb_lock:
} else if (bdi->dev) {
/*
* When bdi tasks are inactive for long time, they are killed.
* In this case we have to wake-up the forker thread which
* should create and run the bdi thread.
*/
trace_writeback_wake_forker_thread(bdi);
If we don't have the lock above, the bdi->dev could potentially be
cleared after the check but before the tracepoint is hit, leading to a
NULL pointer dereference.
next prev parent reply other threads:[~2012-01-20 5:24 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-05 8:49 [PATCH] mm/backing-dev.c: fix crash when USB/SCSI device is detached Chanho Min
2012-01-15 10:28 ` Rabin Vincent
2012-01-15 12:58 ` Wu Fengguang
2012-01-15 15:41 ` Rabin Vincent
2012-01-16 2:53 ` Wu Fengguang
2012-01-16 5:28 ` Chanho Min
2012-01-16 5:50 ` Wu Fengguang
2012-01-16 5:53 ` Wu Fengguang
2012-01-16 6:34 ` Chanho Min
2012-01-18 19:43 ` Rabin Vincent
2012-01-19 16:50 ` [PATCHv2] backing-dev: fix wakeup timer races with bdi_unregister() Rabin Vincent
2012-01-19 23:46 ` Namjae Jeon
2012-01-20 5:24 ` Rabin Vincent [this message]
2012-01-20 6:15 ` Namjae Jeon
2012-01-20 10:03 ` Rabin Vincent
2012-01-20 11:18 ` Namjae Jeon
2012-01-20 12:08 ` Rabin Vincent
2012-01-20 15:04 ` Namjae Jeon
2012-01-31 13:24 ` Wu Fengguang
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