linux-kernel - Re: WARNING in per_cpu

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Message-ID: <20171016134147.iimdj2peykyneklt@lakrids.cambridge.arm.com>
Date:   Mon, 16 Oct 2017 14:41:47 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Shankara Pailoor <sp3485@...umbia.edu>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Andrew Zhu Aday <andrew.aday@...umbia.edu>
Subject: Re: WARNING in per_cpu_alloc

Hi,

On Sun, Oct 15, 2017 at 08:28:55AM -0400, Shankara Pailoor wrote:
> Hi,
> 
> We found the warning when fuzzing with Syzkaller on Linux 4-14-rc4.
> 
> illegal size (32776) or align (8) for percpu allocation
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 22596 at mm/percpu.c:1365 pcpu_alloc+0x140/0x10f0
> Kernel panic - not syncing: panic_on_warn set ...

FWIW, this has already been reported upstream [1]. The suggested fix was
to make pcpu_alloc suport __GFP_NOWARN, but I haven't had the chance to
fix that up yet.

Thanks,
Mark.

[1] https://lkml.kernel.org/r/20170928112727.GA11310@leverpostej

> CPU: 0 PID: 22596 Comm: syz-executor1 Not tainted 4.14.0-rc4 #1
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
> Call Trace:
>  dump_stack+0x115/0x1da
>  panic+0x1b4/0x3a7
>  __warn+0x1c4/0x1d9
>  report_bug+0x211/0x2d0
>  fixup_bug+0x40/0x90
>  do_trap+0x260/0x390
>  do_error_trap+0x11c/0x350
>  do_invalid_op+0x1b/0x20
>  invalid_op+0x18/0x20
> RIP: 0010:pcpu_alloc+0x140/0x10f0
> RSP: 0018:ffff8800a752f6a8 EFLAGS: 00010286
> RAX: 0000000000000037 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000037 RSI: ffffc90001a32000 RDI: ffffed0014ea5ec9
> RBP: ffff8800a752f920 R08: ffff8800a752ed98 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000008007
> R13: 0000000000000000 R14: ffff8800a752fec0 R15: 0000000000000008
>  __alloc_percpu+0x24/0x30
>  dev_map_alloc+0x68e/0xb70
>  SyS_bpf+0xd25/0x4500
>  entry_SYSCALL_64_fastpath+0x1f/0xbe
> RIP: 0033:0x452349
> RSP: 002b:00007f8c38897be8 EFLAGS: 00000212 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 0000000000968000 RCX: 0000000000452349
> RDX: 000000000000001c RSI: 0000000020038000 RDI: 0000000000000000
> RBP: 0000000000000046 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f25a8
> R13: 00000000ffffffff R14: 0000000000968070 R15: 0000000000000000
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: 0x23800000 from 0xffffffff81000000 (relocation range:
> 0xffffffff80000000-0xffffffffbfffffff)
> Rebooting in 86400 seconds..
> 
> Here is the reproducer program: https://pastebin.com/TdSTCu5E
> 
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