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Fri, 28 Aug 2026 15:46:30 -0700 (PDT) Date: Fri, 28 Aug 2026 15:46:30 -0700 X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6a920fc6.1d9ded08.62e62.00f6.GAE@google.com> Subject: [moderation/CI] Re: mm/memcontrol: fix stuck FLUSHING_CACHED_CHARGE bit on isolated cpus From: syzbot ci To: syzkaller-upstream-moderation@googlegroups.com Cc: syzbot@lists.linux.dev Content-Type: text/plain; charset="UTF-8" syzbot ci has tested the following series [v2] mm/memcontrol: fix stuck FLUSHING_CACHED_CHARGE bit on isolated cpus https://lore.kernel.org/all/20260828135036.7d44361f@fangorn * [PATCH v2] mm/memcontrol: fix stuck FLUSHING_CACHED_CHARGE bit on isolated cpus and found the following issue: possible deadlock in blkg_conf_prep Full report is available here: https://ci.syzbot.org/series/b7c6073d-9eac-41ad-921f-a90980058034 *** possible deadlock in blkg_conf_prep tree: mm-new URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git base: 91011cec827788fde4bddbf45ecc507525c2ae06 arch: amd64 compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 config: https://ci.syzbot.org/builds/c13b10a4-7bea-4b4c-a897-542d751e804f/config syz repro: https://ci.syzbot.org/findings/539b38db-9b98-4110-88d1-eee54084fc25/syz_repro ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.0.23/5880 is trying to acquire lock: ffffffff8ee8f800 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:316 [inline] ffffffff8ee8f800 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4636 [inline] ffffffff8ee8f800 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:4974 [inline] ffffffff8ee8f800 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_noprof+0x5f/0x600 mm/slub.c:5010 but task is already holding lock: ffff88810a0b3bc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa3/0xd80 block/blk-cgroup.c:849 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->blkcg_mutex){+.+.}-{4:4}: __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 blkcg_activate_policy+0x1cb/0x8e0 block/blk-cgroup.c:1608 blk_throtl_init+0x2f7/0x420 block/blk-throttle.c:1339 tg_set_conf+0x1db/0x4e0 block/blk-throttle.c:1368 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}: blk_alloc_queue+0x544/0x690 block/blk-core.c:504 blk_mq_alloc_queue block/blk-mq.c:4420 [inline] __blk_mq_alloc_disk+0x194/0x390 block/blk-mq.c:4467 loop_add+0x480/0xb40 drivers/block/loop.c:2071 loop_init+0xd7/0x160 drivers/block/loop.c:2310 do_one_initcall+0x250/0x870 init/main.c:1357 do_initcall_level+0x10a/0x1a0 init/main.c:1419 do_initcalls+0x59/0xa0 init/main.c:1435 kernel_init_freeable+0x29d/0x3e0 init/main.c:1670 kernel_init+0x22/0x1d0 init/main.c:1560 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #0 (fs_reclaim){+.+.}-{0:0}: check_prev_add kernel/locking/lockdep.c:3181 [inline] check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] kmem_cache_alloc_noprof+0x5f/0x600 mm/slub.c:5010 __radix_tree_preload+0x2df/0x870 lib/radix-tree.c:338 blkg_conf_prep+0x621/0xd80 block/blk-cgroup.c:885 tg_set_conf+0x20b/0x4e0 block/blk-throttle.c:1373 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Chain exists of: fs_reclaim --> &q->q_usage_counter(io)#17 --> &q->blkcg_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->blkcg_mutex); lock(&q->q_usage_counter(io)#17); lock(&q->blkcg_mutex); lock(fs_reclaim); *** DEADLOCK *** locks held by syz.0.23/5880: 6, last CPU#1: #0: ffff88816db7d8f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320 fs/file.c:1259 #1: ffff88816ee86460 (sb_writers#10){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2753 [inline] #1: ffff88816ee86460 (sb_writers#10){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683 #2: ffff88816db7ac80 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1d8/0x540 fs/kernfs/file.c:336 #3: ffff88816fe82e18 (kn->active#56){.+.+}-{0:0}, at: kernfs_get_active_of fs/kernfs/file.c:73 [inline] #3: ffff88816fe82e18 (kn->active#56){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x22b/0x540 fs/kernfs/file.c:337 #4: ffff88810a0b3a40 (&q->rq_qos_mutex){+.+.}-{4:4}, at: blkg_conf_open_bdev+0x2a8/0x3c0 block/blk-cgroup.c:806 #5: ffff88810a0b3bc0 (&q->blkcg_mutex){+.+.}-{4:4}, at: blkg_conf_prep+0xa3/0xd80 block/blk-cgroup.c:849 stack backtrace: CPU: 1 UID: 0 PID: 5880 Comm: syz.0.23 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2059 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2191 check_prev_add kernel/locking/lockdep.c:3181 [inline] check_prevs_add kernel/locking/lockdep.c:3300 [inline] validate_chain kernel/locking/lockdep.c:3924 [inline] __lock_acquire+0x15ff/0x2e50 kernel/locking/lockdep.c:5254 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5908 __fs_reclaim_acquire mm/page_alloc.c:4375 [inline] fs_reclaim_acquire+0x71/0x100 mm/page_alloc.c:4389 might_alloc include/linux/sched/mm.h:316 [inline] slab_pre_alloc_hook mm/slub.c:4636 [inline] slab_alloc_node mm/slub.c:4974 [inline] kmem_cache_alloc_noprof+0x5f/0x600 mm/slub.c:5010 __radix_tree_preload+0x2df/0x870 lib/radix-tree.c:338 blkg_conf_prep+0x621/0xd80 block/blk-cgroup.c:885 tg_set_conf+0x20b/0x4e0 block/blk-throttle.c:1373 cgroup_file_write+0x331/0x8f0 kernel/cgroup/cgroup.c:4412 kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x612/0xba0 fs/read_write.c:687 ksys_write+0x150/0x270 fs/read_write.c:739 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f8d5f99e159 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f8d608b0028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f8d5fc25fa0 RCX: 00007f8d5f99e159 RDX: 000000000000006a RSI: 00002000000000c0 RDI: 0000000000000005 RBP: 00007f8d5fa35024 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f8d5fc26038 R14: 00007f8d5fc25fa0 R15: 00007ffd10d387c8 *** If these findings have caused you to resend the series or submit a separate fix, please add the following tag to your commit message: Tested-by: syzbot@syzkaller.appspotmail.com --- This report is generated by a bot. It may contain errors. syzbot ci engineers can be reached at syzkaller@googlegroups.com. To test a fix for this bug, please reply with `#syz test` (on a separate line) and attach the patch to the email. Notes: - The patch will be applied on top of the tested series (as an incremental fix). - To test a new version of the whole series, please send it directly to syzbot@lists.linux.dev. - Arguments like custom git repos and branches are not supported. The email will later be sent to: [akpm@linux-foundation.org cgroups@vger.kernel.org hannes@cmpxchg.org kernel-team@meta.com linux-kernel@vger.kernel.org linux-mm@kvack.org mhocko@kernel.org muchun.song@linux.dev riel@surriel.com roman.gushchin@linux.dev shakeel.butt@linux.dev] If the report looks fine to you, reply with: #syz upstream If the report is a false positive, reply with #syz invalid