linux-kernel - Re: [syzbot] [mm?] WARNING in alloc_frozen_pages

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Message-ID: <aJwZPq0b2rckG-ap@codewreck.org>
Date: Wed, 13 Aug 2025 13:49:02 +0900
From: Dominique Martinet <asmadeus@...ewreck.org>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: syzbot <syzbot+3f9768ec54c86997ddfb@...kaller.appspotmail.com>,
	akpm@...ux-foundation.org, apopple@...dia.com, byungchul@...com,
	david@...hat.com, gourry@...rry.net, joshua.hahnjy@...il.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	matthew.brost@...el.com, rakie.kim@...com,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Latchesar Ionkov <lucho@...kov.net>,
	Christian Schoenebeck <linux_oss@...debyte.com>,
	syzkaller-bugs@...glegroups.com, ying.huang@...ux.alibaba.com,
	ziy@...dia.com
Subject: Re: [syzbot] [mm?] WARNING in alloc_frozen_pages_noprof

Harry Yoo wrote on Wed, Aug 13, 2025 at 09:31:34AM +0900:
> The warning is:
> 
> 	/*
> 	 * There are several places where we assume that the order value is sane
> 	 * so bail out early if the request is out of bound.
> 	 */
> 	if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp))
> 		return NULL;
> 
> There's not much the buddy allocator can do when a user requests
> order > MAX_PAGE_ORDER allocations.
> 
> >  alloc_pages_mpol+0x1e4/0x460 mm/mempolicy.c:2416
> >  alloc_frozen_pages_noprof+0xe0/0x210 mm/mempolicy.c:2487
> >  ___kmalloc_large_node+0xac/0x154 mm/slub.c:4306
> >  __kmalloc_large_node_noprof+0x2c/0x8c mm/slub.c:4337
> >  __do_kmalloc_node mm/slub.c:4353 [inline]
> >  __kmalloc_noprof+0x3bc/0x4c8 mm/slub.c:4377
> >  kmalloc_noprof include/linux/slab.h:909 [inline]
> >  kzalloc_noprof include/linux/slab.h:1039 [inline]
> >  v9fs_fid_get_acl+0x64/0x114 fs/9p/acl.c:32
> 
> So... 9p FS shouldn't really request that?
> 
> Cc'ing 9p FS folks.

Thanks for the Cc.

So, this comes up once in a while, everytime we discuss limiting the
xattr size, then someone says we should do something else or I'm using
the wrong define or I don't remember and then when I ask what we should
do never reply again.

See [1] or [2] for the last two time this happened.
[1] https://lore.kernel.org/all/20240304-xattr_maxsize-v1-1-322357ec6bdf@codewreck.org/T/#u
[2] https://lore.kernel.org/lkml/20240202121319.21743-1-pchelkin@ispras.ru/

I'll be happy to take any patch you send (or one of the older patches if
you tell me which is "correct"), I don't care anymore.
-- 
Dominique