Re: [PATCH 1/2] ARC: show_regs: avoid page allocator

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Vineet Gupta <vineet.gupta1@synopsys.com>,
	Eugeniy Paltsev <eugeniy.paltsev@synopsys.com>,
	"linux-snps-arc@lists.infradead.org"
	<linux-snps-arc@lists.infradead.org>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 1/2] ARC: show_regs: avoid page allocator
Date: Thu, 20 Dec 2018 22:30:08 +0900	[thread overview]
Message-ID: <e2d2c160-0ef6-5504-7824-032a5c70fa7f@I-love.SAKURA.ne.jp> (raw)
Message-ID: <20181220133008.GbEQjjTeolBC_IFDlk4XvcyPiAn1a5X51R43jKQqVzk@z> (raw)
In-Reply-To: <49f9edc9-87ee-1efc-58f8-b0d9a52c8a49@synopsys.com>

On 2018/12/20 10:16, Vineet Gupta wrote:
> On 12/19/18 9:04 AM, Eugeniy Paltsev wrote:
>> As I can see x86 use print_vma_addr() in their show_signal_msg()
>> function which allocate page with __get_free_page(GFP_NOWAIT);
> 
> Indeed with that the __get_free_page() lockdep splat is gone.
> 
> There's a different one now hence my other patch.
> 
> | [ARCLinux]# ./segv-null-ptr
> | potentially unexpected fatal signal 11.
> | BUG: sleeping function called from invalid context at kernel/fork.c:1011
> | in_atomic(): 1, irqs_disabled(): 0, pid: 70, name: segv-null-ptr
> | no locks held by segv-null-ptr/70.
> | CPU: 0 PID: 70 Comm: segv-null-ptr Not tainted 4.18.0+ #69
> |
> | Stack Trace:
> |  arc_unwind_core+0xcc/0x100
> |  ___might_sleep+0x17a/0x190
> |  mmput+0x16/0xb8

Then, does mmput_async() help?

> |  show_regs+0x52/0x310
> |  get_signal+0x5ee/0x610
> |  do_signal+0x2c/0x218
> |  resume_user_mode_begin+0x90/0xd8