From: Brian King <brking@us.ibm.com>
To: Chris Wright <chrisw@osdl.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: call_usermodehelper hang
Date: Tue, 06 Apr 2004 20:46:38 -0500 [thread overview]
Message-ID: <40735D7E.2090304@us.ibm.com> (raw)
In-Reply-To: <20040406174150.D22989@build.pdx.osdl.net>
Chris Wright wrote:
> * Brian King (brking@us.ibm.com) wrote:
>
>>I have been running into some kernel hangs due to call_usermodehelper. Looking
>>at the backtrace, it looks to me like there are deadlock issues with adding
>>devices from work queues. Attached is a sample backtrace from one of the
>>hangs I experienced. My question is why does call_usermodehelper do 2 different
>>things depending on whether or not it is called from the kevent task? It appears
>>that the simple way to fix the hang would be to never have call_usermodehelper
>>use a work_queue since it must be called from process context anyway, or
>>am I missing something?
>
>
> It does two different things because it's trying to run from keventd.
> In the case that current is not keventd, it schedules the work, so
> keventd will pick that work up later to run in it's process context.
>
> How early is this hang?
Pretty early. Boot time, loading scsi drivers. While initializing the
third scsi adapter on the system a device shows up dynamically on the
first adapter, the LLD schedules work to call scsi_add_device and we
end up with the hang.
It looks like init thread adds work and waits
> for it's completion while holding a semaphore. It is never woken up by
> keventd which is sleeping waiting for wakeup from semaphore that init
> thread took.
>
> Seems troubling to hold the sem while calling call_usermodehelper, as that
> could go off for a long time.
I agree. There is another similar hang I ran into recently with the scsi
core in that I was calling scsi_add_device from keventd, which ended up
sleeping on the scan_mutex since the module load process was calling
scsi_scan_host. scsi_scan_host was in the same kobject hotplug code,
calling call_usermodehelper. I figured my LLD shouldn't be doing that,
so I synchronized the events. Perhaps that was the wrong fix... I
suppose I could have changed the LLD to always call
scsi_scan_host/scsi_add_device/etc. from keventd...
-Brian
next prev parent reply other threads:[~2004-04-07 1:46 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-04-06 18:11 call_usermodehelper hang Brian King
2004-04-07 0:29 ` Andrew Morton
2004-04-07 6:11 ` Greg KH
2004-04-07 14:00 ` Brian King
2004-04-07 22:58 ` [PATCH] " Brian King
2004-04-08 22:47 ` Greg KH
2004-04-09 20:42 ` Brian King
2004-04-09 20:53 ` Greg KH
2004-04-09 21:05 ` Brian King
2004-04-09 21:15 ` Andrew Morton
2004-04-10 16:53 ` Greg KH
2004-04-10 20:11 ` Andrew Morton
2004-04-12 15:25 ` Brian King
2004-04-12 17:46 ` Andrew Morton
2004-04-16 17:55 ` Brian King
2004-04-12 18:49 ` Greg KH
2004-04-08 23:17 ` Chris Wright
2004-04-07 0:41 ` Chris Wright
2004-04-07 1:46 ` Brian King [this message]
[not found] <4072E2F5.9060604@us.ibm.com>
2004-04-16 8:52 ` Heiko Carstens
2004-04-16 14:06 ` Brian King
2005-02-25 17:17 Payasam Manohar
2005-02-25 18:06 ` Lee Revell
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