From: Vegard Nossum <vegard.nossum@oracle.com>
To: Guenter Roeck <linux@roeck-us.net>,
Oleg Nesterov <oleg@redhat.com>,
Ralf Baechle <ralf@linux-mips.org>
Cc: Jamie Iles <jamie.iles@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: mips qemu test failures in -next due to "kthread: Fix use-after-free if kthread fork fails"
Date: Sun, 28 May 2017 16:49:10 +0200 [thread overview]
Message-ID: <1d1770a7-f1d7-d3ab-3522-92aaf1099171@oracle.com> (raw)
In-Reply-To: <dc237f28-a065-2eee-5c99-20e130c080e5@oracle.com>
On 05/28/17 13:45, Vegard Nossum wrote:
> On 05/27/17 19:56, Guenter Roeck wrote:
>> Hi,
>>
>> my qemu testis of mips images are failing in -next. Symptom is a hang
>> during
>> boot; see http://kerneltests.org/builders/qemu-mips-next for some
>> examples.
>>
>> I bisected the problem in next-20170526. It points to commit
>> 4d6501dce079c
>> ("kthread: Fix use-after-free if kthread fork fails"). Reverting that
>> patch
>> fixes the problem.
>>
>> Bisect log is attached.
>
> Hi,
>
> Thanks for the report and sorry for the breakage :-/
>
> I can't immediately spot what's going wrong, but I am able to reproduce
> it on mips so I will try to debug.
>
> Are you sure it's this commit, though? I checked out linus/master and
> I get a boot hang even after reverting it.
My mistake; I ran into a different bug which made me think it was
hanging when it wasn't.
However, I think I found the problem; does this patch fix it for you too?
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 918d4c73e951..5351e1f3950d 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -120,7 +120,6 @@ int copy_thread_tls(unsigned long clone_flags,
unsigned long usp,
struct thread_info *ti = task_thread_info(p);
struct pt_regs *childregs, *regs = current_pt_regs();
unsigned long childksp;
- p->set_child_tid = p->clear_child_tid = NULL;
childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;
The problem is that when we moved the p->{set,clear}_child_tid
assignments inside copy_process(), the above assignments would clear
them out. The assignments only exist on mips and openrisc (which would
need the same patch), which explains why I didn't see it in my x86
testing. I think the patch above should be safe given that we're now
always setting these fields in copy_process() at an appropriate moment.
Looks like those assignments came from commit 3c37026d43c47 ("NPTL,
round one."); Ralf?
Oleg?
Vegard
next prev parent reply other threads:[~2017-05-28 14:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-27 17:56 mips qemu test failures in -next due to "kthread: Fix use-after-free if kthread fork fails" Guenter Roeck
2017-05-28 11:45 ` Vegard Nossum
2017-05-28 14:44 ` Guenter Roeck
2017-05-28 14:49 ` Vegard Nossum [this message]
2017-05-28 15:00 ` Guenter Roeck
2017-05-28 15:26 ` Guenter Roeck
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