• Josef Bacik's avatar
    btrfs: allocate new inode in NOFS context · 11a19a90
    Josef Bacik authored
    A user reported a lockdep splat
    
     ======================================================
     WARNING: possible circular locking dependency detected
     5.2.11-gentoo #2 Not tainted
     ------------------------------------------------------
     kswapd0/711 is trying to acquire lock:
     000000007777a663 (sb_internal){.+.+}, at: start_transaction+0x3a8/0x500
    
    but task is already holding lock:
     000000000ba86300 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30
    
    which lock already depends on the new lock.
    
    the existing dependency chain (in reverse order) is:
    
    -> #1 (fs_reclaim){+.+.}:
     kmem_cache_alloc+0x1f/0x1c0
     btrfs_alloc_inode+0x1f/0x260
     alloc_inode+0x16/0xa0
     new_inode+0xe/0xb0
     btrfs_new_inode+0x70/0x610
     btrfs_symlink+0xd0/0x420
     vfs_symlink+0x9c/0x100
     do_symlinkat+0x66/0xe0
     do_syscall_64+0x55/0x1c0
     entry_SYSCALL_64_after_hwframe+0x49/0xbe
    
    -> #0 (sb_internal){.+.+}:
     __sb_start_write+0xf6/0x150
     start_transaction+0x3a8/0x500
     btrfs_commit_inode_delayed_inode+0x59/0x110
     btrfs_evict_inode+0x19e/0x4c0
     evict+0xbc/0x1f0
     inode_lru_isolate+0x113/0x190
     __list_lru_walk_one.isra.4+0x5c/0x100
     list_lru_walk_one+0x32/0x50
     prune_icache_sb+0x36/0x80
     super_cache_scan+0x14a/0x1d0
     do_shrink_slab+0x131/0x320
     shrink_node+0xf7/0x380
     balance_pgdat+0x2d5/0x640
     kswapd+0x2ba/0x5e0
     kthread+0x147/0x160
     ret_from_fork+0x24/0x30
    
    other info that might help us debug this:
    
     Possible unsafe locking scenario:
    
     CPU0 CPU1
     ---- ----
     lock(fs_reclaim);
     lock(sb_internal);
     lock(fs_reclaim);
     lock(sb_internal);
    *** DEADLOCK ***
    
     3 locks held by kswapd0/711:
     #0: 000000000ba86300 (fs_reclaim){+.+.}, at: __fs_reclaim_acquire+0x0/0x30
     #1: 000000004a5100f8 (shrinker_rwsem){++++}, at: shrink_node+0x9a/0x380
     #2: 00000000f956fa46 (&type->s_umount_key#30){++++}, at: super_cache_scan+0x35/0x1d0
    
    stack backtrace:
     CPU: 7 PID: 711 Comm: kswapd0 Not tainted 5.2.11-gentoo #2
     Hardware name: Dell Inc. Precision Tower 3620/0MWYPT, BIOS 2.4.2 09/29/2017
     Call Trace:
     dump_stack+0x85/0xc7
     print_circular_bug.cold.40+0x1d9/0x235
     __lock_acquire+0x18b1/0x1f00
     lock_acquire+0xa6/0x170
     ? start_transaction+0x3a8/0x500
     __sb_start_write+0xf6/0x150
     ? start_transaction+0x3a8/0x500
     start_transaction+0x3a8/0x500
     btrfs_commit_inode_delayed_inode+0x59/0x110
     btrfs_evict_inode+0x19e/0x4c0
     ? var_wake_function+0x20/0x20
     evict+0xbc/0x1f0
     inode_lru_isolate+0x113/0x190
     ? discard_new_inode+0xc0/0xc0
     __list_lru_walk_one.isra.4+0x5c/0x100
     ? discard_new_inode+0xc0/0xc0
     list_lru_walk_one+0x32/0x50
     prune_icache_sb+0x36/0x80
     super_cache_scan+0x14a/0x1d0
     do_shrink_slab+0x131/0x320
     shrink_node+0xf7/0x380
     balance_pgdat+0x2d5/0x640
     kswapd+0x2ba/0x5e0
     ? __wake_up_common_lock+0x90/0x90
     kthread+0x147/0x160
     ? balance_pgdat+0x640/0x640
     ? __kthread_create_on_node+0x160/0x160
     ret_from_fork+0x24/0x30
    
    This is because btrfs_new_inode() calls new_inode() under the
    transaction.  We could probably move the new_inode() outside of this but
    for now just wrap it in memalloc_nofs_save().
    Reported-by: default avatarZdenek Sojka <zsojka@seznam.cz>
    Fixes: 712e36c5 ("btrfs: use GFP_KERNEL in btrfs_alloc_inode")
    CC: stable@vger.kernel.org # 4.16+
    Reviewed-by: default avatarFilipe Manana <fdmanana@suse.com>
    Signed-off-by: default avatarJosef Bacik <josef@toxicpanda.com>
    Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
    11a19a90
inode.c 298 KB