From: Arnd Bergmann <arnd@arndb.de>
To: Olaf Hering <olaf@aepfle.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: acquire_console_mutex: WARNING: at 2.6.33.4-rt20/kernel/mutex-debug.c:65 mutex_remove_waiter+0xe8/0x11c()
Date: Tue, 25 May 2010 13:18:37 +0200 [thread overview]
Message-ID: <201005251318.37242.arnd@arndb.de> (raw)
In-Reply-To: <20100524225357.GA19513@aepfle.de>
On Tuesday 25 May 2010, Olaf Hering wrote:
> I get this warning when busybox /sbin/init opens the console.
> It does not happen when CONFIG_PREEMPT_RT is enabled.
> Any ideas how to fix it for CONFIG_PREEMPT_DESKTOP?
>
> [ 16.450000] ------------[ cut here ]------------
> [ 16.450000] WARNING: at /work/rt/linux-2.6.33-rt/kernel/mutex-debug.c:65 mutex_remove_waiter+0xe8/0x11c()
> [ 16.450000] Modules linked in:
> [ 16.450000] [<c0033e68>] (unwind_backtrace+0x0/0xdc) from [<c0324994>] (dump_stack+0x18/0x1c)
> [ 16.450000] [<c0324994>] (dump_stack+0x18/0x1c) from [<c0049aec>] (warn_slowpath_common+0x50/0x68)
> [ 16.450000] [<c0049aec>] (warn_slowpath_common+0x50/0x68) from [<c0049b1c>] (warn_slowpath_null+0x18/0x1c)
> [ 16.450000] [<c0049b1c>] (warn_slowpath_null+0x18/0x1c) from [<c006d640>] (mutex_remove_waiter+0xe8/0x11c)
> [ 16.450000] [<c006d640>] (mutex_remove_waiter+0xe8/0x11c) from [<c032709c>] (mutex_lock_nested+0x268/0x304)
> [ 16.450000] [<c032709c>] (mutex_lock_nested+0x268/0x304) from [<c004a2d8>] (acquire_console_mutex+0x40/0x68)
> [ 16.450000] [<c004a2d8>] (acquire_console_mutex+0x40/0x68) from [<c01d8420>] (con_open+0x18/0xc4)
> [ 16.450000] [<c01d8420>] (con_open+0x18/0xc4) from [<c01c80dc>] (tty_open+0x398/0x55c)
> [ 16.450000] [<c01c80dc>] (tty_open+0x398/0x55c) from [<c00ae628>] (chrdev_open+0x198/0x1bc)
> [ 16.450000] [<c00ae628>] (chrdev_open+0x198/0x1bc) from [<c00a9928>] (__dentry_open+0x188/0x294)
> [ 16.450000] [<c00a9928>] (__dentry_open+0x188/0x294) from [<c00a9b04>] (nameidata_to_filp+0x48/0x60)
> [ 16.450000] [<c00a9b04>] (nameidata_to_filp+0x48/0x60) from [<c00b795c>] (do_filp_open+0x42c/0x8a8)
> [ 16.450000] [<c00b795c>] (do_filp_open+0x42c/0x8a8) from [<c00a968c>] (do_sys_open+0x64/0x11c)
> [ 16.450000] [<c00a968c>] (do_sys_open+0x64/0x11c) from [<c00a977c>] (sys_open+0x24/0x28)
> [ 16.450000] [<c00a977c>] (sys_open+0x24/0x28) from [<c002e000>] (ret_fast_syscall+0x0/0x34)
> [ 16.450000] ---[ end trace cdbe849ecfa1acdf ]---
>
> The used config is shown after dmesg.
As a wild guess, this might happen because we drop the BKL in
mutex_lock_nested and might need to wait for it when we got the lock.
The reason that this surfaces in -rt would be that the console_sem
is replaced with a proper mutex there, on non-rt kernels this would
be invisible.
You could try to pull in the blk/tty branch from
http://git.kernel.org/?p=linux/kernel/git/arnd/playground.git and enable
CONFIG_TTY_MUTEX to see if that gives you better lockdep output,
because that replaces the implicit dropping of the BKL with mutex operations
that lockdep is aware of.
Arnd
next prev parent reply other threads:[~2010-05-25 11:18 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-24 22:53 acquire_console_mutex: WARNING: at 2.6.33.4-rt20/kernel/mutex-debug.c:65 mutex_remove_waiter+0xe8/0x11c() Olaf Hering
2010-05-25 11:18 ` Arnd Bergmann [this message]
2010-05-30 21:39 ` Olaf Hering
2010-05-31 11:29 ` Arnd Bergmann
2010-06-02 9:13 ` Olaf Hering
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