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b=LCZRO966MJXtXlmSnshT6skldVpCIVltLpzcANgImksrNBMw4dR0xcJfeHpjJixW6 /kLRDerxNAmBzlCUo+jtAldaykUQ3uGfcpfuCWVlmpjJjSz0B6vjzyBddSxi6twTrE RUbUTdwWJBLX58EqtVnMHKXUEFgHN+FjKK1xGa1U= Date: Tue, 22 Sep 2026 19:08:50 -0700 From: Andrew Morton To: Dominique Martinet Cc: syzbot , apopple@nvidia.com, byungchul@sk.com, david@kernel.org, gourry@gourry.net, joshua.hahnjy@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, matthew.brost@intel.com, rakie.kim@sk.com, syzkaller-bugs@googlegroups.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, Eric Van Hensbergen , Latchesar Ionkov , Christian Schoenebeck , v9fs@lists.linux.dev, Nguyen Ngoc Thang Subject: Re: [syzbot] [mm?] WARNING in v9fs_fid_get_acl (2) Message-Id: <20260922190850.02e782b7196791602163a3a9@linux-foundation.org> In-Reply-To: References: <6aae188b.71f81b7d.15fa6d.0004.GAE@google.com> <20260919031451.3f47a8da8405e88fa1ab5398@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: em7ibsd6gsz99rzxpocpcjpicp5ps3n9 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 6FF0E20002 X-HE-Tag: 1790129332-510590 X-HE-Meta: U2FsdGVkX19wfiCFpTVHSODZ42MZ9BlLfT+YShCAOqI5jxmKHlaXC/dFg206OfYOQZD7JKbUDBzcgKiqKRNLTYtXrebfSVGIfw3GFIZilIZQbfjf25dp/O9zM81X6VwJuae7OPlJu6XSCMWGc8LHh7BoaS2PzjL3S5fNQrnqzVbuDDUUv7Psk9KFtlK7sw2q4BJNBjTNGljgZd1EpgPs/+9Hf6tHfNFyj12sFvuDPYex8bYA+Kfw9gpPs/En94ebkr2G/yNEMLm9WYlnDuPgByxJits0yC3wWZanVBMq2HR7oS3HwcLu/4b5zyskXTdAHwLRfFPNx2gAE1sGqQZTcbBKQrjhlWiEFfuvC18Z8cgF2yPQ8Fnf7KDYlRR0SDtJ6qWYFvNaOWxJXUdc56IUkoxdOuI6hme7y0ltRBl9FzyKaWus4a12phmbvjI/FA3R5D+YJTdXZLZGeoHRQIiJOEXA1k1jRoqAT41IdKrN/O3K/TnNnPQYQXClZLVBTyKZM7w+yq4qZTYA/bYf/un1vTicIVy61+3cjeUP22Y/0jwa76ZRCi0/v0KFtPiqdLynfFXCEcqHgqiApOkEj+lvMNr8Vr1TB805wij14mX/mcpWKvDf9TuUYMB7wTXHhZaoafLyYiCzQex6hIAqq+jV/1PUwhHj2b8hrEp3im+M8/zG8yk9FCGuPcEc61ejRYQcZ4y/CUv4jhTECKb56WjTNi+6a9ZH8tVWNS0hoaANWEEJEygb0WaYJlbR3/uOmJsWi/lb6lev6kQtGYYsjSmgHmQaxcW3W3ISoMOGSAZ/05u/yWnnmfnSk+LgP6AcbDH6I1hLWM5dCPNdV6bWr8aV+X+1kq2kUgI8L4Gk4llgWPV9i43uUYgIv75mt2DVJ/faOk6nX7HGn207nFmtbsz+aLqzrNjUPC+T7E+Kp0OSdyVC87VMzPWXQ43fLLgWl+hQg+oCE9uY9e5pNGpDPvu 7sRWhZ98 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 22 Sep 2026 17:45:14 +0900 Dominique Martinet wrote: > (+Nguyen in Cc as he tried resending sloppy patches after this) > > Andrew Morton wrote on Sat, Sep 19, 2026 at 03:14:51AM -0700: > > > WARNING: mm/page_alloc.c:5340 at alloc_order_allowed mm/page_alloc.c:5340 [inline], CPU#0: syz.1.357/7872 > > > WARNING: mm/page_alloc.c:5340 at __alloc_frozen_pages_noprof+0x2137/0x3300 mm/page_alloc.c:5397, CPU#0: syz.1.357/7872 > > > > Thanks. Caused by an old v9fs bug. A fix was proposed but never merged: > > https://lists.openwall.net/linux-kernel/2024/02/02/806?utm_source=chatgpt.com > > Right, we've been going in circle with this since forever, and nobody > answered Christian Schoenebeck's question[1] about what the limit should > be, and while I don't care much ultimately I sort of agree with him > (e.g. limit should be XATTR_SIZE_MAX for anything that the VFS layer > touches, but acl are converted within the 9p subsystem and could be > arbitrarily large so status quo of a KMALLOC_MAX_SIZE limit because they > could come from something else) > > Andrew, if you have an opinion on whether we should cap the acl sizes > anyway, please say... whome. Well, if the converted ACLs can be large and it's hard to figure out how large then yes, some pre-canned limit is difficult. So it's OK to leave the decision up to kmalloc() and just put a (nicely commented!) __GFP_NOWARN in there. otoh, if we're permitting workloads to trigger a large number of large allocations then that might be a problem from a utilization or even DoS point of view.