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From: Shakeel Butt To: syzbot Cc: akpm@linux-foundation.org, axelrasmussen@google.com, david@kernel.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, mhocko@kernel.org, syzkaller-bugs@googlegroups.com, weixugc@google.com, yuanchu@google.com, zhengqi.arch@bytedance.com, brauner@kernel.org, djwong@kernel.org, jack@suse.cz Subject: Re: [syzbot] [mm?] possible deadlock in rhashtable_free_and_destroy Message-ID: References: <69e798fe.050a0220.24bfd3.0032.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69e798fe.050a0220.24bfd3.0032.GAE@google.com> X-Migadu-Flow: FLOW_OUT Ccing relevant folks as this seems related to recent change of moving simple_xattrs from rbtree to rhastable. On Tue, Apr 21, 2026 at 08:34:22AM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 8541d8f725c6 Merge tag 'mtd/for-7.1' of git://git.kernel.o.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=15380836580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=7e54da1916e8d11f > dashboard link: https://syzkaller.appspot.com/bug?extid=5af806780f38a5fe691f > compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-8541d8f7.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/22dfea2c37c2/vmlinux-8541d8f7.xz > kernel image: https://storage.googleapis.com/syzbot-assets/e2f93ad68fe3/bzImage-8541d8f7.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+5af806780f38a5fe691f@syzkaller.appspotmail.com > > ====================================================== > WARNING: possible circular locking dependency detected > syzkaller #0 Tainted: G L > ------------------------------------------------------ > kswapd0/108 is trying to acquire lock: > ffff888056f3c4e8 (&ht->mutex){+.+.}-{4:4}, at: rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154 > > but task is already holding lock: > ffffffff8e9b0800 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xb5d/0x1ac0 mm/vmscan.c:7102 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #1 (fs_reclaim){+.+.}-{0:0}: > __fs_reclaim_acquire mm/page_alloc.c:4327 [inline] > fs_reclaim_acquire+0xc4/0x100 mm/page_alloc.c:4341 > might_alloc include/linux/sched/mm.h:317 [inline] > slab_pre_alloc_hook mm/slub.c:4520 [inline] > slab_alloc_node mm/slub.c:4875 [inline] > __do_kmalloc_node mm/slub.c:5294 [inline] > __kvmalloc_node_noprof+0xcc/0xa00 mm/slub.c:6828 > bucket_table_alloc.isra.0+0x88/0x460 lib/rhashtable.c:186 > rhashtable_rehash_alloc+0x68/0x110 lib/rhashtable.c:368 > rht_deferred_worker+0x1d9/0x1fd0 lib/rhashtable.c:429 > process_one_work+0xa0e/0x1980 kernel/workqueue.c:3302 > process_scheduled_works kernel/workqueue.c:3385 [inline] > worker_thread+0x5ef/0xe50 kernel/workqueue.c:3466 > kthread+0x370/0x450 kernel/kthread.c:436 > ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > -> #0 (&ht->mutex){+.+.}-{4:4}: > check_prev_add kernel/locking/lockdep.c:3165 [inline] > check_prevs_add kernel/locking/lockdep.c:3284 [inline] > validate_chain kernel/locking/lockdep.c:3908 [inline] > __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237 > lock_acquire kernel/locking/lockdep.c:5868 [inline] > lock_acquire+0x1b1/0x370 kernel/locking/lockdep.c:5825 > __mutex_lock_common kernel/locking/mutex.c:632 [inline] > __mutex_lock+0x1a4/0x1b10 kernel/locking/mutex.c:806 The cancel_work_sync(&ht->run_work) in rhashtable_free_and_destroy() should avoid concurrent mutex lockers from rht_deferred_worker(). Seems like false positive as all rhastables share single static lockdep class for the ht->mutex. Simple fix would be to move rhashtable_rehash_alloc() to use NOFS allocation or we can introduce more fine grained lockdep classes for rhashtables. > rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154 > shmem_evict_inode+0x1ae/0xc40 mm/shmem.c:1429 > evict+0x3c2/0xad0 fs/inode.c:841 > iput_final fs/inode.c:1960 [inline] > iput.part.0+0x605/0xf50 fs/inode.c:2009 > iput+0x35/0x40 fs/inode.c:1975 > dentry_unlink_inode+0x2a1/0x490 fs/dcache.c:467 > __dentry_kill+0x1d0/0x600 fs/dcache.c:670 > finish_dput+0x76/0x480 fs/dcache.c:879 > dput.part.0+0x456/0x570 fs/dcache.c:928 > dput+0x1f/0x30 fs/dcache.c:920 > ovl_destroy_inode+0x3e/0x190 fs/overlayfs/super.c:217 > destroy_inode+0xcb/0x1c0 fs/inode.c:394 > evict+0x599/0xad0 fs/inode.c:865 > iput_final fs/inode.c:1960 [inline] > iput.part.0+0x605/0xf50 fs/inode.c:2009 > iput+0x35/0x40 fs/inode.c:1975 > dentry_unlink_inode+0x2a1/0x490 fs/dcache.c:467 > __dentry_kill+0x1d0/0x600 fs/dcache.c:670 > shrink_kill fs/dcache.c:1147 [inline] > shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1174 > prune_dcache_sb+0xea/0x150 fs/dcache.c:1256 > super_cache_scan+0x328/0x550 fs/super.c:223 > do_shrink_slab+0x416/0x1240 mm/shrinker.c:440 > shrink_slab_memcg mm/shrinker.c:557 [inline] > shrink_slab+0xa7d/0x12e0 mm/shrinker.c:635 > shrink_one+0x398/0x7f0 mm/vmscan.c:4932 > shrink_many mm/vmscan.c:4993 [inline] > lru_gen_shrink_node mm/vmscan.c:5071 [inline] > shrink_node+0x2673/0x3dc0 mm/vmscan.c:6059 > kswapd_shrink_node mm/vmscan.c:6913 [inline] > balance_pgdat+0xaaf/0x1ac0 mm/vmscan.c:7089 > kswapd+0x557/0xb60 mm/vmscan.c:7362 > kthread+0x370/0x450 kernel/kthread.c:436 > ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > other info that might help us debug this: > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(fs_reclaim); > lock(&ht->mutex); > lock(fs_reclaim); > lock(&ht->mutex); > > *** DEADLOCK *** > > 2 locks held by kswapd0/108: > #0: ffffffff8e9b0800 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0xb5d/0x1ac0 mm/vmscan.c:7102 > #1: ffff88801347c0d8 (&type->s_umount_key#76){++++}-{4:4}, at: super_trylock_shared fs/super.c:565 [inline] > #1: ffff88801347c0d8 (&type->s_umount_key#76){++++}-{4:4}, at: super_cache_scan+0x98/0x550 fs/super.c:198 > > stack backtrace: > CPU: 2 UID: 0 PID: 108 Comm: kswapd0 Tainted: G L syzkaller #0 PREEMPT(full) > Tainted: [L]=SOFTLOCKUP > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 > Call Trace: > > __dump_stack lib/dump_stack.c:94 [inline] > dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 > print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043 > check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175 > check_prev_add kernel/locking/lockdep.c:3165 [inline] > check_prevs_add kernel/locking/lockdep.c:3284 [inline] > validate_chain kernel/locking/lockdep.c:3908 [inline] > __lock_acquire+0x14b8/0x2630 kernel/locking/lockdep.c:5237 > lock_acquire kernel/locking/lockdep.c:5868 [inline] > lock_acquire+0x1b1/0x370 kernel/locking/lockdep.c:5825 > __mutex_lock_common kernel/locking/mutex.c:632 [inline] > __mutex_lock+0x1a4/0x1b10 kernel/locking/mutex.c:806 > rhashtable_free_and_destroy+0x3d/0x9b0 lib/rhashtable.c:1154 > shmem_evict_inode+0x1ae/0xc40 mm/shmem.c:1429 > evict+0x3c2/0xad0 fs/inode.c:841 > iput_final fs/inode.c:1960 [inline] > iput.part.0+0x605/0xf50 fs/inode.c:2009 > iput+0x35/0x40 fs/inode.c:1975 > dentry_unlink_inode+0x2a1/0x490 fs/dcache.c:467 > __dentry_kill+0x1d0/0x600 fs/dcache.c:670 > finish_dput+0x76/0x480 fs/dcache.c:879 > dput.part.0+0x456/0x570 fs/dcache.c:928 > dput+0x1f/0x30 fs/dcache.c:920 > ovl_destroy_inode+0x3e/0x190 fs/overlayfs/super.c:217 > destroy_inode+0xcb/0x1c0 fs/inode.c:394 > evict+0x599/0xad0 fs/inode.c:865 > iput_final fs/inode.c:1960 [inline] > iput.part.0+0x605/0xf50 fs/inode.c:2009 > iput+0x35/0x40 fs/inode.c:1975 > dentry_unlink_inode+0x2a1/0x490 fs/dcache.c:467 > __dentry_kill+0x1d0/0x600 fs/dcache.c:670 > shrink_kill fs/dcache.c:1147 [inline] > shrink_dentry_list+0x180/0x5e0 fs/dcache.c:1174 > prune_dcache_sb+0xea/0x150 fs/dcache.c:1256 > super_cache_scan+0x328/0x550 fs/super.c:223 > do_shrink_slab+0x416/0x1240 mm/shrinker.c:440 > shrink_slab_memcg mm/shrinker.c:557 [inline] > shrink_slab+0xa7d/0x12e0 mm/shrinker.c:635 > shrink_one+0x398/0x7f0 mm/vmscan.c:4932 > shrink_many mm/vmscan.c:4993 [inline] > lru_gen_shrink_node mm/vmscan.c:5071 [inline] > shrink_node+0x2673/0x3dc0 mm/vmscan.c:6059 > kswapd_shrink_node mm/vmscan.c:6913 [inline] > balance_pgdat+0xaaf/0x1ac0 mm/vmscan.c:7089 > kswapd+0x557/0xb60 mm/vmscan.c:7362 > kthread+0x370/0x450 kernel/kthread.c:436 > ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 > > > > --- > This report is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@googlegroups.com. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the report is already addressed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want to overwrite report's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the report is a duplicate of another one, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup