linux-kernel - Re: [Kernel Bug] WARNING in mempool_alloc

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Message-ID: <aYHFZ5OxfL4j-_ze@hyeyoo>
Date: Tue, 3 Feb 2026 18:52:39 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vernon Yang <vernon2gm@...il.com>
Cc: 李龙兴 <coregee2000@...il.com>,
        syzkaller@...glegroups.com, vbabka@...e.cz, akpm@...ux-foundation.org,
        cl@...two.org, rientjes@...gle.com, roman.gushchin@...ux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [Kernel Bug] WARNING in mempool_alloc_noprof

On Tue, Feb 03, 2026 at 11:47:46AM +0800, Vernon Yang wrote:
> On 2026-02-02, Harry Yoo wrote:
> > On Mon, Feb 02, 2026 at 02:40:14PM +0800, 李龙兴 wrote:
> > > Dear Linux kernel developers and maintainers,
> > >
> > > We would like to report a new kernel bug found by our tool. WARNING in
> > > mempool_alloc_noprof. Details are as follows.
> > >
> > > Kernel commit: v6.12.11
> > > Kernel config: see attachment
> > > report: see attachment
> > >
> > > We are currently analyzing the root cause and  working on a
> > > reproducible PoC. We will provide further updates in this thread as
> > > soon as we have more information.
> > >
> > > Best regards,
> > > Longxing Li
> > >
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 1 PID: 362734 at mm/page_alloc.c:4234
> > > __alloc_pages_slowpath mm/page_alloc.c:4234 [inline]
> > > WARNING: CPU: 1 PID: 362734 at mm/page_alloc.c:4234
> > > __alloc_pages_noprof+0x2025/0x25a0 mm/page_alloc.c:4766
> > > Modules linked in:
> > > CPU: 1 UID: 0 PID: 362734 Comm: syz-executor.5 Not tainted 6.12.11 #1
> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> > > RIP: 0010:__alloc_pages_slowpath mm/page_alloc.c:4234 [inline]
> > > RIP: 0010:__alloc_pages_noprof+0x2025/0x25a0 mm/page_alloc.c:4766
> >
> > page allocator triggers a warning when __GFP_NOFAIL is set but
> > __GFP_DIRECT_RECLAIM is not set.
> >
> > > Code: 10 00 00 00 44 8b 74 24 48 41 89 c5 0f b6 c0 44 8b a4 24 84 00
> > > 00 00 89 44 24 28 e9 e5 f6 ff ff 90 0f 0b 90 e9 f1 f6 ff ff 90 <0f> 0b
> > > 90 e9 1e fb ff ff e8 2e a4 38 09 e9 5e ed ff ff 4c 89 f7 e8
> > > RSP: 0000:ffffc9003ce9e7d0 EFLAGS: 00010246
> > > RAX: 0000000000008000 RBX: 0000000000000000 RCX: ffffc9003ce9e8fc
> > > RDX: 0000000000000000 RSI: 0000000000000002 RDI: ffff88813fff99c8
> > > RBP: 0000000000000000 R08: 000000000000028d R09: 0000000000000000
> > > R10: ffff88807fffbc17 R11: 0000000000000000 R12: 000000000009a800
> > > R13: 000000000009a800 R14: 1ffff920079d3d0e R15: 0000000000000001
> > > FS:  00007f1784eff640(0000) GS:ffff888135e00000(0000) knlGS:0000000000000000
> > > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 000055bb25a85a28 CR3: 0000000096938000 CR4: 0000000000752ef0
> > > PKRU: 55555554
> > > Call Trace:
> > >  <TASK>
> > >  alloc_pages_mpol_noprof+0x2c9/0x610 mm/mempolicy.c:2269
> > >  mempool_alloc_noprof+0x176/0x390 mm/mempool.c:402
> >
> > the user of the mempool (f2fs_encrypt_one_page) passed __GFP_DIRECT_RECLAIM,
> > but mempool temporarily cleared it, but not __GFP_NOFAIL:
> >    gfp_temp = gfp_mask & ~(__GFP_DIRECT_RECLAIM|__GFP_IO)
> >
> > Hmm perhaps mempool should clear __GFP_NOFAIL as well when clearing
> > __GFP_DIRECT_RECLAIM?
> 
> LGTM. I wrote a fix pacth, as below.
> 
> ---
> 
> From 9131e1b26b1ec55dd38ab08512ed6da0fa7a21f0 Mon Sep 17 00:00:00 2001
> From: Vernon Yang <yanglincheng@...inos.cn>
> Date: Tue, 3 Feb 2026 10:51:45 +0800
> Subject: [PATCH] mm: mempool: remove __GFP_NOFAIL gfp_mask when first
>  allocation
> 
> page allocator triggers a warning when __GFP_NOFAIL is set but
> __GFP_DIRECT_RECLAIM is not set.
> 
> The user of the mempool (f2fs_encrypt_one_page) passed
> __GFP_DIRECT_RECLAIM, but mempool temporarily cleared it when
> first allocate memory.
> 
>     gfp_temp = gfp_mask & ~(__GFP_DIRECT_RECLAIM|__GFP_IO)
> 
> Make mempool also clear __GFP_NOFAIL as well when clearing
> __GFP_DIRECT_RECLAIM.
> 
> Closes: https://lore.kernel.org/linux-mm/CAHPqNmwK9TY5THsXWkJuYCdt7x*mZHPq65AUOLZJeMp-FdAMvA@mail.gmail.com
> Suggested-by: Harry Yoo <harry.yoo@...cle.com>
> Signed-off-by: Vernon Yang <yanglincheng@...inos.cn>
> ---

Maybe the changelog could be rephrased a bit,
but overall LGTM, thanks!

>  mm/mempool.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mempool.c b/mm/mempool.c
> index c290e5261b47..679ab4a2cc5f 100644
> --- a/mm/mempool.c
> +++ b/mm/mempool.c
> @@ -472,7 +472,7 @@ static unsigned int mempool_alloc_from_pool(struct mempool *pool, void **elems,
>  static inline gfp_t mempool_adjust_gfp(gfp_t *gfp_mask)
>  {
>  	*gfp_mask |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
> -	return *gfp_mask & ~(__GFP_DIRECT_RECLAIM | __GFP_IO);
> +	return *gfp_mask & ~(__GFP_NOFAIL | __GFP_DIRECT_RECLAIM | __GFP_IO);
>  }
> 
>  /**
> --