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Tue, 8 Jul 2025 08:50:31 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id tNGDF9fbbGgXXgAAD6G6ig (envelope-from ); Tue, 08 Jul 2025 08:50:31 +0000 Message-ID: <5397779c-9a89-4dd3-9937-208fefb58f78@suse.cz> Date: Tue, 8 Jul 2025 10:50:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] WARNING in xfs_init_fs_context To: Dave Chinner Cc: Tetsuo Handa , Zi Yan , Barry Song , Carlos Maiolino , linux-xfs@vger.kernel.org, syzbot , akpm@linux-foundation.org, apopple@nvidia.com, byungchul@sk.com, david@redhat.com, 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, Harry Yoo , Michal Hocko , Matthew Wilcox References: <6861c281.a70a0220.3b7e22.0ab8.GAE@google.com> <1921ec99-7abb-42f1-a56b-d1f0f5bc1377@I-love.SAKURA.ne.jp> <630b4379-751a-4bf1-a249-f2e051ec77d6@suse.cz> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: f713aykpycibnathg4myfwugr5ejs6n3 X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6C5D5C0012 X-HE-Tag: 1751964633-629371 X-HE-Meta: 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 sd5Ttsk9 vSWZPFCE63Vq0+o0cDFHhk5cr6ZD0etALSixbMHuu2qOdd2tUgHD1QjOwP3pRPUm33hjIoWko7UjLqapGc5stXh169ZDlveeefalGLI9aXUFFUjuTlQJoKOkDwK0aU22IKEch3FrAB9YIf/SyDqDjwfC5pYY/QS+HEBwqAZWQMYUY+lLwiovliqwkj7Cif3lp00IzD+TowdBbhFeI+N+wnNoVR+VRZK0FZn/ATEpLl7FncywzGWEwu3VmqQs1CjrqsuupZ0EeguqmmrVdmbs04PGKsorGbQC86+6/WhHouorJ45TeevzXOBUuPCQeLk6kGb/8bSow3NIe6ptbTe+IklQlefbr61WtUJThoxtr5swNDyiBp+SYN8A2Y0eg5rQU7CtUARfrzLfzBpVIhQlghNaekON8CaujfRD0xWfYrXwoJUXWjKeafvw4nBtodixpVkAyr0vO4vLzQLxXtcx6m9PN5fZWC1vvFAGQ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/8/25 00:10, Dave Chinner wrote: > On Wed, Jul 02, 2025 at 09:30:30AM +0200, Vlastimil Babka wrote: >> On 7/2/25 3:41 AM, Tetsuo Handa wrote: >> > By the way, why is xfs_init_fs_context() using __GFP_NOFAIL ? >> > >> > mp = kzalloc(sizeof(struct xfs_mount), GFP_KERNEL | __GFP_NOFAIL); >> > if (!mp) >> > return -ENOMEM; >> > >> > This looks an allocation attempt which can fail safely. > > It's irrelevant - it shouldn't fail regardless of __GFP_NOFAIL being > specified. If you mean the "too small to fail" behavior then it's generally true, except in some corner cases like being an oom victim, in which case the allocation can fail - the userspace process is doomed anyway. But a (small) kernel allocation not handling NULL would still need __GFP_NOFAIL to prevent that corner case. >> Indeed. Dave Chinner's commit f078d4ea82760 ("xfs: convert kmem_alloc() >> to kmalloc()") dropped the xfs wrapper. This allocation didn't use >> KM_MAYFAIL so it got __GFP_NOFAIL. The commit mentions this high-order >> nofail issue for another allocation site that had to use xlog_kvmalloc(). > > I don't see how high-order allocation behaviour is relevant here. > > Pahole says the struct xfs_mount is 4224 bytes in length. It is an > order-1 allocation and if we've fragmented memory so badly that slab > can't allocate an order-1 page then *lots* of other stuff is going > to be stalling. (e.g. slab pages for inodes are typically order-3, > same as the kmalloc-8kk slab). Elsewhere in this thread we figured it out since I wrote the quoted reply. 4224 bytes means kmalloc-8k where the fallback allocation (the one that passes on the __GFP_NOFAIL) order is 1 normally. But due to KASAN enabled its metadata means the per-object size goes above 8k and thus the fallback order will be 2. It's a corner case that wasn't anticipated and existed for years without known reports. We'll need to deal with it somehow. > Note that the size of the structure is largely because of the > embedded cpumask for inodegc: > > struct cpumask m_inodegc_cpumask; /* 3104 1024 */ > > This should probably be pulled out into a dynamically allocated > inodegc specific structure. Then the struct xfs_mount is only a > order-0 allocation and should never fail, regardless of > __GFP_NOFAIL being specified or not. > >> I think either this allocation really can fail as the code (return >> -ENOMEM) suggests and thus can drop __GFP_NOFAIL, or it can use >> kvmalloc() - I think the wrapper for that can be removed now too after >> the discussion in [1] resulted in commit 46459154f997 ("mm: kvmalloc: >> make kmalloc fast path real fast path"). > > I know about that - I have patches that I'm testing that replace > xlog_kvmalloc() with kvmalloc calls. Great, thanks! > -Dave.