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Message-ID: <20150506235936.GB23822@cloud>
Date: Wed, 6 May 2015 16:59:36 -0700
From: josh@...htriplett.org
To: Fengguang Wu <fengguang.wu@...el.com>
Cc: Iulia Manda <iulia.manda21@...il.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linux Memory Management List <linux-mm@...ck.org>,
LKP <lkp@...org>, linux-kernel@...r.kernel.org
Subject: Re: [CONFIG_MULTIUSER] BUG: unable to handle kernel paging request
at ffffffee
On Wed, May 06, 2015 at 08:44:29AM -0700, Josh Triplett wrote:
> On Wed, May 06, 2015 at 05:08:50PM +0800, Fengguang Wu wrote:
> > FYI, the reported bug is still not fixed in linux-next 20150506.
>
> This isn't the same bug. The previous one you mentioned was a userspace
> assertion failure in libnih, likely caused because some part of upstart
> didn't have appropriate error handling for some syscall returning
> ENOSYS; that one wasn't an issue, since CONFIG_MULTIUSER=n is not
> expected to boot a standard Linux distribution.
>
> This one, on the other hand, is a kernel panic, and does need fixing.
>
> > commit 2813893f8b197a14f1e1ddb04d99bce46817c84a
> >
> > +-----------------------------------------------------------+------------+------------+------------+
> > | | c79574abe2 | 2813893f8b | cbdacaf0c1 |
> > +-----------------------------------------------------------+------------+------------+------------+
> > | boot_successes | 60 | 0 | 0 |
> > | boot_failures | 0 | 22 | 1064 |
> > | BUG:unable_to_handle_kernel | 0 | 22 | 1032 |
> > | Oops | 0 | 22 | 1032 |
> > | EIP_is_at_devpts_new_index | 0 | 22 | 1032 |
> > | Kernel_panic-not_syncing:Fatal_exception | 0 | 22 | 1032 |
> > | backtrace:do_sys_open | 0 | 22 | 1032 |
> > | backtrace:SyS_open | 0 | 22 | 1032 |
> > | WARNING:at_arch/x86/kernel/fpu/core.c:#fpu__clear() | 0 | 0 | 32 |
> > | Kernel_panic-not_syncing:Attempted_to_kill_init!exitcode= | 0 | 0 | 32 |
> > +-----------------------------------------------------------+------------+------------+------------+
>
> Is this table saying the number of times the type of error in the first
> column occurred in each commit?
>
> In any case, investigating. Iulia, can you look at this as well?
>
> I'm digging through the call stack, and I'm having a hard time seeing
> how the CONFIG_MULTIUSER patch could affect anything here.
Update: it looks like init_devpts_fs is getting ERR_PTR(-EINVAL) back
from kern_mount and storing that in devpts_mnt; later, devpts_new_index
pokes at devpts_mnt and explodes.
So, there are two separate bugs here. On the one hand, CONFIG_MULTIUSER
should not be causing kern_mount to fail with -EINVAL; tracking that
down now. On the other hand, devpts and ptmx should handle the failure
better, without crashing; ptmx_open should have gracefully failed back
to userspace with -ENODEV or something, since ptmx doesn't make sense
without devpts. I'll send a patch for that too.
- Josh Triplett
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