linux-kernel - Re: [PATCH] printk: use kvmalloc instead of kmalloc for devkmsg

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Message-ID: <YS4jqsSlD7UySNRA@alley>
Date:   Tue, 31 Aug 2021 14:42:18 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     이용택 <ytk.lee@...sung.com>
Cc:     "senozhatsky@...omium.org" <senozhatsky@...omium.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "john.ogness@...utronix.de" <john.ogness@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] printk: use kvmalloc instead of kmalloc for devkmsg_user

On Mon 2021-08-30 16:17:01, 이용택 wrote:
> Size of struct devkmsg_user increased to 16784 by commit 896fbe20b4e2
> ("printk: use the lockless ringbuffer") so order3(32kb) is needed for
> kmalloc. Under stress conditions the kernel may temporary fail to
> allocate 32k with kmalloc. Use kvmalloc instead of kmalloc to aviod
> this issue.
> 
> qseecomd invoked oom-killer: gfp_mask=0x40cc0(GFP_KERNEL|__GFP_COMP), order=3, oom_score_adj=-1000
> Call trace:
>  dump_backtrace+0x0/0x34c
>  dump_stack_lvl+0xd4/0x16c
>  dump_header+0x5c/0x338
>  out_of_memory+0x374/0x4cc
>  __alloc_pages_slowpath+0xbc8/0x1130
>  __alloc_pages_nodemask+0x170/0x1b0
>  kmalloc_order+0x5c/0x24c
>  devkmsg_open+0x1f4/0x558
>  memory_open+0x94/0xf0
>  chrdev_open+0x288/0x3dc
>  do_dentry_open+0x2b4/0x618
>  path_openat+0xce4/0xfa8
>  do_filp_open+0xb0/0x164
>  do_sys_openat2+0xa8/0x264
>  __arm64_sys_openat+0x70/0xa0
>  el0_svc_common+0xc4/0x270
>  el0_svc+0x34/0x9c
>  el0_sync_handler+0x88/0xf0
>  el0_sync+0x1bc/0x200
> 
>  DMA32: 4521*4kB (UMEC) 1377*8kB (UMECH) 73*16kB (UM) 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 30268kB
>  Normal: 2490*4kB (UMEH) 277*8kB (UMH) 27*16kB (UH) 1*32kB (H) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 12640kB
> 
> Signed-off-by: Yong-Taek Lee <ytk.lee@...sung.com>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr