Hello, so this lockdep report looks real but is more related to OOM handling than to ext4 as such. The immediate problem I can see is that mem_cgroup_print_oom_meminfo() which is called under oom_lock calls memory_stat_format() which does GFP_KERNEL allocations to allocate buffers for dumping of MM statistics. This creates oom_lock -> fs reclaim dependency and because OOM can be hit (and thus oom_lock acquired) in practically any allocation (regardless of GFP_NOFS) this has a potential of creating real deadlock cycles. So should mem_cgroup_print_oom_meminfo() be using memalloc_nofs_save/restore() to avoid such deadlocks? Or perhaps someone sees another solution? Generally allocating memory to report OOM looks a bit dangerous to me ;). Honza On Thu 14-07-22 05:08:26, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 5a29232d870d Merge tag 'for-5.19-rc6-tag' of git://git.ker.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=16619ce8080000 > kernel config: https://syzkaller.appspot.com/x/.config?x=525bc0635a2b942a > dashboard link: https://syzkaller.appspot.com/bug?extid=2d2aeadc6ce1e1f11d45 > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > userspace arch: i386 > > Unfortunately, I don't have any reproducer for this issue yet. > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+2d2aeadc6ce1e1f11d45@xxxxxxxxxxxxxxxxxxxxxxxxx > > ====================================================== > WARNING: possible circular locking dependency detected > 5.19.0-rc6-syzkaller-00026-g5a29232d870d #0 Not tainted > ------------------------------------------------------ > khugepaged/48 is trying to acquire lock: > ffff888044598990 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xfb4/0x14a0 fs/jbd2/transaction.c:461 > > but task is already holding lock: > ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __perform_reclaim mm/page_alloc.c:4638 [inline] > ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline] > ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0x9e1/0x2160 mm/page_alloc.c:5066 > > which lock already depends on the new lock. > > > the existing dependency chain (in reverse order) is: > > -> #2 (fs_reclaim){+.+.}-{0:0}: > __fs_reclaim_acquire mm/page_alloc.c:4589 [inline] > fs_reclaim_acquire+0x115/0x160 mm/page_alloc.c:4603 > might_alloc include/linux/sched/mm.h:271 [inline] > slab_pre_alloc_hook mm/slab.h:723 [inline] > slab_alloc_node mm/slub.c:3157 [inline] > slab_alloc mm/slub.c:3251 [inline] > kmem_cache_alloc_trace+0x40/0x3f0 mm/slub.c:3282 > kmalloc include/linux/slab.h:600 [inline] > memory_stat_format+0x95/0xae0 mm/memcontrol.c:1468 > mem_cgroup_print_oom_meminfo.cold+0x50/0x7e mm/memcontrol.c:1594 > dump_header+0x13f/0x7f9 mm/oom_kill.c:462 > oom_kill_process.cold+0x10/0x15 mm/oom_kill.c:1037 > out_of_memory+0x358/0x14b0 mm/oom_kill.c:1175 > mem_cgroup_out_of_memory+0x206/0x270 mm/memcontrol.c:1650 > memory_max_write+0x25c/0x3b0 mm/memcontrol.c:6299 > cgroup_file_write+0x1de/0x770 kernel/cgroup/cgroup.c:3882 > kernfs_fop_write_iter+0x3f8/0x610 fs/kernfs/file.c:290 > call_write_iter include/linux/fs.h:2058 [inline] > new_sync_write+0x38a/0x560 fs/read_write.c:504 > vfs_write+0x7c0/0xac0 fs/read_write.c:591 > ksys_write+0x127/0x250 fs/read_write.c:644 > do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline] > __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178 > do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203 > entry_SYSENTER_compat_after_hwframe+0x53/0x62 > > -> #1 (oom_lock){+.+.}-{3:3}: > __mutex_lock_common kernel/locking/mutex.c:603 [inline] > __mutex_lock+0x12f/0x1350 kernel/locking/mutex.c:747 > mem_cgroup_out_of_memory+0x8d/0x270 mm/memcontrol.c:1640 > mem_cgroup_oom mm/memcontrol.c:1880 [inline] > try_charge_memcg+0xef9/0x1380 mm/memcontrol.c:2670 > obj_cgroup_charge_pages mm/memcontrol.c:2999 [inline] > obj_cgroup_charge+0x2ab/0x5e0 mm/memcontrol.c:3289 > memcg_slab_pre_alloc_hook mm/slab.h:505 [inline] > slab_pre_alloc_hook mm/slab.h:728 [inline] > slab_alloc_node mm/slub.c:3157 [inline] > slab_alloc mm/slub.c:3251 [inline] > __kmem_cache_alloc_lru mm/slub.c:3258 [inline] > kmem_cache_alloc+0x92/0x3b0 mm/slub.c:3268 > kmem_cache_zalloc include/linux/slab.h:723 [inline] > alloc_buffer_head+0x20/0x140 fs/buffer.c:3294 > alloc_page_buffers+0x285/0x7a0 fs/buffer.c:829 > grow_dev_page fs/buffer.c:965 [inline] > grow_buffers fs/buffer.c:1011 [inline] > __getblk_slow+0x525/0x1080 fs/buffer.c:1038 > __getblk_gfp+0x6e/0x80 fs/buffer.c:1333 > sb_getblk include/linux/buffer_head.h:326 [inline] > ext4_getblk+0x20d/0x7c0 fs/ext4/inode.c:866 > ext4_bread+0x2a/0x1c0 fs/ext4/inode.c:912 > ext4_append+0x177/0x3a0 fs/ext4/namei.c:67 > ext4_init_new_dir+0x25e/0x4d0 fs/ext4/namei.c:2920 > ext4_mkdir+0x3cf/0xb20 fs/ext4/namei.c:2966 > vfs_mkdir+0x1c3/0x3b0 fs/namei.c:3975 > do_mkdirat+0x285/0x300 fs/namei.c:4001 > __do_sys_mkdirat fs/namei.c:4016 [inline] > __se_sys_mkdirat fs/namei.c:4014 [inline] > __ia32_sys_mkdirat+0x81/0xa0 fs/namei.c:4014 > do_syscall_32_irqs_on arch/x86/entry/common.c:112 [inline] > __do_fast_syscall_32+0x65/0xf0 arch/x86/entry/common.c:178 > do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:203 > entry_SYSENTER_compat_after_hwframe+0x53/0x62 > > -> #0 (jbd2_handle){++++}-{0:0}: > check_prev_add kernel/locking/lockdep.c:3095 [inline] > check_prevs_add kernel/locking/lockdep.c:3214 [inline] > validate_chain kernel/locking/lockdep.c:3829 [inline] > __lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053 > lock_acquire kernel/locking/lockdep.c:5665 [inline] > lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630 > start_this_handle+0xfe7/0x14a0 fs/jbd2/transaction.c:463 > jbd2__journal_start+0x399/0x930 fs/jbd2/transaction.c:520 > __ext4_journal_start_sb+0x3a8/0x4a0 fs/ext4/ext4_jbd2.c:105 > __ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline] > ext4_dirty_inode+0x9d/0x110 fs/ext4/inode.c:5949 > __mark_inode_dirty+0x495/0x1050 fs/fs-writeback.c:2381 > mark_inode_dirty_sync include/linux/fs.h:2337 [inline] > iput.part.0+0x57/0x820 fs/inode.c:1767 > iput+0x58/0x70 fs/inode.c:1760 > dentry_unlink_inode+0x2b1/0x460 fs/dcache.c:401 > __dentry_kill+0x3c0/0x640 fs/dcache.c:607 > shrink_dentry_list+0x23c/0x800 fs/dcache.c:1201 > prune_dcache_sb+0xe7/0x140 fs/dcache.c:1282 > super_cache_scan+0x336/0x590 fs/super.c:104 > do_shrink_slab+0x42d/0xbd0 mm/vmscan.c:770 > shrink_slab+0x17c/0x6f0 mm/vmscan.c:930 > shrink_node_memcgs mm/vmscan.c:3124 [inline] > shrink_node+0x8b3/0x1db0 mm/vmscan.c:3245 > shrink_zones mm/vmscan.c:3482 [inline] > do_try_to_free_pages+0x3b5/0x1700 mm/vmscan.c:3540 > try_to_free_pages+0x2ac/0x840 mm/vmscan.c:3775 > __perform_reclaim mm/page_alloc.c:4641 [inline] > __alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline] > __alloc_pages_slowpath.constprop.0+0xa8a/0x2160 mm/page_alloc.c:5066 > __alloc_pages+0x436/0x510 mm/page_alloc.c:5439 > __alloc_pages_node include/linux/gfp.h:587 [inline] > khugepaged_alloc_page+0xa0/0x170 mm/khugepaged.c:859 > collapse_huge_page mm/khugepaged.c:1062 [inline] > khugepaged_scan_pmd mm/khugepaged.c:1348 [inline] > khugepaged_scan_mm_slot mm/khugepaged.c:2170 [inline] > khugepaged_do_scan mm/khugepaged.c:2251 [inline] > khugepaged+0x3473/0x66a0 mm/khugepaged.c:2296 > kthread+0x2e9/0x3a0 kernel/kthread.c:376 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302 > > other info that might help us debug this: > > Chain exists of: > jbd2_handle --> oom_lock --> fs_reclaim > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(fs_reclaim); > lock(oom_lock); > lock(fs_reclaim); > lock(jbd2_handle); > > *** DEADLOCK *** > > 3 locks held by khugepaged/48: > #0: ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __perform_reclaim mm/page_alloc.c:4638 [inline] > #0: ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline] > #0: ffffffff8bebdb20 (fs_reclaim){+.+.}-{0:0}, at: __alloc_pages_slowpath.constprop.0+0x9e1/0x2160 mm/page_alloc.c:5066 > #1: ffffffff8be7d850 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0xc9/0x6f0 mm/vmscan.c:920 > #2: ffff8880445800e0 (&type->s_umount_key#33){++++}-{3:3}, at: trylock_super fs/super.c:415 [inline] > #2: ffff8880445800e0 (&type->s_umount_key#33){++++}-{3:3}, at: super_cache_scan+0x6c/0x590 fs/super.c:79 > > stack backtrace: > CPU: 2 PID: 48 Comm: khugepaged Not tainted 5.19.0-rc6-syzkaller-00026-g5a29232d870d #0 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 > check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175 > check_prev_add kernel/locking/lockdep.c:3095 [inline] > check_prevs_add kernel/locking/lockdep.c:3214 [inline] > validate_chain kernel/locking/lockdep.c:3829 [inline] > __lock_acquire+0x2abe/0x5660 kernel/locking/lockdep.c:5053 > lock_acquire kernel/locking/lockdep.c:5665 [inline] > lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630 > start_this_handle+0xfe7/0x14a0 fs/jbd2/transaction.c:463 > jbd2__journal_start+0x399/0x930 fs/jbd2/transaction.c:520 > __ext4_journal_start_sb+0x3a8/0x4a0 fs/ext4/ext4_jbd2.c:105 > __ext4_journal_start fs/ext4/ext4_jbd2.h:326 [inline] > ext4_dirty_inode+0x9d/0x110 fs/ext4/inode.c:5949 > __mark_inode_dirty+0x495/0x1050 fs/fs-writeback.c:2381 > mark_inode_dirty_sync include/linux/fs.h:2337 [inline] > iput.part.0+0x57/0x820 fs/inode.c:1767 > iput+0x58/0x70 fs/inode.c:1760 > dentry_unlink_inode+0x2b1/0x460 fs/dcache.c:401 > __dentry_kill+0x3c0/0x640 fs/dcache.c:607 > shrink_dentry_list+0x23c/0x800 fs/dcache.c:1201 > prune_dcache_sb+0xe7/0x140 fs/dcache.c:1282 > super_cache_scan+0x336/0x590 fs/super.c:104 > do_shrink_slab+0x42d/0xbd0 mm/vmscan.c:770 > shrink_slab+0x17c/0x6f0 mm/vmscan.c:930 > shrink_node_memcgs mm/vmscan.c:3124 [inline] > shrink_node+0x8b3/0x1db0 mm/vmscan.c:3245 > shrink_zones mm/vmscan.c:3482 [inline] > do_try_to_free_pages+0x3b5/0x1700 mm/vmscan.c:3540 > try_to_free_pages+0x2ac/0x840 mm/vmscan.c:3775 > __perform_reclaim mm/page_alloc.c:4641 [inline] > __alloc_pages_direct_reclaim mm/page_alloc.c:4663 [inline] > __alloc_pages_slowpath.constprop.0+0xa8a/0x2160 mm/page_alloc.c:5066 > __alloc_pages+0x436/0x510 mm/page_alloc.c:5439 > __alloc_pages_node include/linux/gfp.h:587 [inline] > khugepaged_alloc_page+0xa0/0x170 mm/khugepaged.c:859 > collapse_huge_page mm/khugepaged.c:1062 [inline] > khugepaged_scan_pmd mm/khugepaged.c:1348 [inline] > khugepaged_scan_mm_slot mm/khugepaged.c:2170 [inline] > khugepaged_do_scan mm/khugepaged.c:2251 [inline] > khugepaged+0x3473/0x66a0 mm/khugepaged.c:2296 > kthread+0x2e9/0x3a0 kernel/kthread.c:376 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302 > </TASK> > > > --- > 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@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
