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Date:   Thu, 30 Jul 2020 09:58:42 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Zhaoyang Huang <huangzhaoyang@gmail.com>
Cc:     Ingo Molnar <mingo@redhat.com>, chunyan.zhang@unisoc.com,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] trace : use kvmalloc instead of kmalloc
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On Thu, 30 Jul 2020 19:04:12 +0800
Zhaoyang Huang <huangzhaoyang@gmail.com> wrote:

> High order memory stuff within trace could introduce OOM, use kvmalloc instead.
> 
> Please find the bellowing for the call stack we run across in an android system. The scenario happens when traced_probes is woken up to get a large quantity of trace even if free memory is even higher than watermark_low. 

Please limit your column width in the description of patches to 76
characters.

> 
> traced_probes invoked oom-killer: gfp_mask=0x140c0c0(GFP_KERNEL|__GFP_COMP|__GFP_ZERO), nodemask=(null),  order=2, oom_score_adj=-1
> 

What does this traced_probes thing do?

> traced_probes cpuset=system-background mems_allowed=0
> CPU: 3 PID: 588 Comm: traced_probes Tainted: G        W  O    4.14.181 #1
> Hardware name: Generic DT based system
> (unwind_backtrace) from [<c010d824>] (show_stack+0x20/0x24)
> (show_stack) from [<c0b2e174>] (dump_stack+0xa8/0xec)
> (dump_stack) from [<c027d584>] (dump_header+0x9c/0x220)
> (dump_header) from [<c027cfe4>] (oom_kill_process+0xc0/0x5c4)
> (oom_kill_process) from [<c027cb94>] (out_of_memory+0x220/0x310)
> (out_of_memory) from [<c02816bc>] (__alloc_pages_nodemask+0xff8/0x13a4)
> (__alloc_pages_nodemask) from [<c02a6a1c>] (kmalloc_order+0x30/0x48)
> (kmalloc_order) from [<c02a6a64>] (kmalloc_order_trace+0x30/0x118)
> (kmalloc_order_trace) from [<c0223d7c>] (tracing_buffers_open+0x50/0xfc)
> (tracing_buffers_open) from [<c02e6f58>] (do_dentry_open+0x278/0x34c)
> (do_dentry_open) from [<c02e70d0>] (vfs_open+0x50/0x70)
> (vfs_open) from [<c02f7c24>] (path_openat+0x5fc/0x169c)
> (path_openat) from [<c02f75c4>] (do_filp_open+0x94/0xf8)
> (do_filp_open) from [<c02e7650>] (do_sys_open+0x168/0x26c)
> (do_sys_open) from [<c02e77bc>] (SyS_openat+0x34/0x38)
> (SyS_openat) from [<c0108bc0>] (ret_fast_syscall+0x0/0x28)
> 
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> ---
> changes since v1: change kfree to kvfree
> ---
>  kernel/trace/trace.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ca1ee65..8d70c79 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6891,7 +6891,7 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)
>  	if (trace_array_get(tr) < 0)
>  		return -ENODEV;
>  
> -	info = kzalloc(sizeof(*info), GFP_KERNEL);
> +	info = kvmalloc(sizeof(*info), GFP_KERNEL);

The above is a bug. It converts kzalloc() to kvmalloc() instead of
kvzalloc().

-- Steve


>  	if (!info) {
>  		trace_array_put(tr);
>  		return -ENOMEM;
> @@ -7017,7 +7017,7 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
>  	if (info->spare)
>  		ring_buffer_free_read_page(iter->trace_buffer->buffer,
>  					   info->spare_cpu, info->spare);
> -	kfree(info);
> +	kvfree(info);
>  
>  	mutex_unlock(&trace_types_lock);
>