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[49.180.184.88]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-31c21e75e14sm312152a91.25.2025.07.07.15.10.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Jul 2025 15:10:56 -0700 (PDT) Received: from dave by dread.disaster.area with local (Exim 4.98.2) (envelope-from ) id 1uYu32-00000008Bdy-3NwV; Tue, 08 Jul 2025 08:10:52 +1000 Date: Tue, 8 Jul 2025 08:10:52 +1000 From: Dave Chinner To: Vlastimil Babka 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 Subject: Re: [syzbot] [mm?] WARNING in xfs_init_fs_context Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <630b4379-751a-4bf1-a249-f2e051ec77d6@suse.cz> X-Rspamd-Queue-Id: 464521A000A X-Stat-Signature: w5y5uzb7zm7rfryjr8snuo74mh6nbjur X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1751926258-996539 X-HE-Meta: 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 hVsAuefy 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 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 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. > 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). 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. -Dave. -- Dave Chinner david@fromorbit.com