Date:   Sat, 25 Dec 2021 05:53:59 +0000
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, hch@lst.de, cl@linux.com,
        John.p.donnelly@oracle.com, kexec@lists.infradead.org,
        penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com,
        vbabka@suse.cz, David.Laight@aculab.com, david@redhat.com,
        x86@kernel.org, bp@alien8.de
Subject: Re: [PATCH v4 3/3] mm/page_alloc.c: do not warn allocation failure
 on zone DMA if no managed pages
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References: <20211223094435.248523-1-bhe@redhat.com>
 <20211223094435.248523-4-bhe@redhat.com>
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On Thu, Dec 23, 2021 at 05:44:35PM +0800, Baoquan He wrote:
> In kdump kernel of x86_64, page allocation failure is observed:
> 
>  kworker/u2:2: page allocation failure: order:0, mode:0xcc1(GFP_KERNEL|GFP_DMA), nodemask=(null),cpuset=/,mems_allowed=0
>  CPU: 0 PID: 55 Comm: kworker/u2:2 Not tainted 5.16.0-rc4+ #5
>  Hardware name: AMD Dinar/Dinar, BIOS RDN1505B 06/05/2013
>  Workqueue: events_unbound async_run_entry_fn
>  Call Trace:
>   <TASK>
>   dump_stack_lvl+0x48/0x5e
>   warn_alloc.cold+0x72/0xd6
>   __alloc_pages_slowpath.constprop.0+0xc69/0xcd0
>   __alloc_pages+0x1df/0x210
>   new_slab+0x389/0x4d0
>   ___slab_alloc+0x58f/0x770
>   __slab_alloc.constprop.0+0x4a/0x80
>   kmem_cache_alloc_trace+0x24b/0x2c0
>   sr_probe+0x1db/0x620
>   ......
>   device_add+0x405/0x920
>   ......
>   __scsi_add_device+0xe5/0x100
>   ata_scsi_scan_host+0x97/0x1d0
>   async_run_entry_fn+0x30/0x130
>   process_one_work+0x1e8/0x3c0
>   worker_thread+0x50/0x3b0
>   ? rescuer_thread+0x350/0x350
>   kthread+0x16b/0x190
>   ? set_kthread_struct+0x40/0x40
>   ret_from_fork+0x22/0x30
>   </TASK>
>  Mem-Info:
>  ......
> 
> The above failure happened when calling kmalloc() to allocate buffer with
> GFP_DMA. It requests to allocate slab page from DMA zone while no managed
> pages at all in there.
>  sr_probe()
>  --> get_capabilities()
>      --> buffer = kmalloc(512, GFP_KERNEL | GFP_DMA);
> 
> Because in the current kernel, dma-kmalloc will be created as long as
> CONFIG_ZONE_DMA is enabled. However, kdump kernel of x86_64 doesn't have
> managed pages on DMA zone since commit 6f599d84231f ("x86/kdump: Always
> reserve the low 1M when the crashkernel option is specified"). The failure
> can be always reproduced.
> 
> For now, let's mute the warning of allocation failure if requesting pages
> from DMA zone while no managed pages.
> 
> Fixes: 6f599d84231f ("x86/kdump: Always reserve the low 1M when the crashkernel option is specified")
> Cc: stable@vger.kernel.org
> Signed-off-by: Baoquan He <bhe@redhat.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/page_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7c7a0b5de2ff..843bc8e5550a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4204,7 +4204,8 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
>  	va_list args;
>  	static DEFINE_RATELIMIT_STATE(nopage_rs, 10*HZ, 1);
>  
> -	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs))
> +	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs) ||
> +		(gfp_mask & __GFP_DMA) && !has_managed_dma())
>  		return;
>

Warning when there's always no page in DMA zone is unnecessary 
and it confuses user.

The patch looks good.
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

And there is some driers that allocate memory with GFP_DMA
even if that flag is unnecessary. We need to do cleanup later.

Baoquan Are you planning to do it soon?
I want to help that.

Merry Christmas,
Hyeonggon

>  	va_start(args, fmt);
> -- 
> 2.26.3
> 
>