Btrfs: do not take cleanup_work_sem in btrfs_run_delayed_iputs()
Josef has suggested that this is not necessary. Removing it also avoids
this lockdep splat (after the new sb_internal locking stuff was added):
[ 604.090449] ======================================================
[ 604.114819] [ INFO: possible circular locking dependency detected ]
[ 604.139262] 3.6.0-rc2-ceph-00144-g463b030 #1 Not tainted
[ 604.162193] -------------------------------------------------------
[ 604.186139] btrfs-cleaner/6669 is trying to acquire lock:
[ 604.209555] (sb_internal#2){.+.+..}, at: [<ffffffffa0042b84>] start_transaction+0x124/0x430 [btrfs]
[ 604.257100]
[ 604.257100] but task is already holding lock:
[ 604.300366] (&fs_info->cleanup_work_sem){.+.+..}, at: [<ffffffffa0048002>] btrfs_run_delayed_iputs+0x72/0x130 [btrfs]
[ 604.352989]
[ 604.352989] which lock already depends on the new lock.
[ 604.352989]
[ 604.427104]
[ 604.427104] the existing dependency chain (in reverse order) is:
[ 604.478493]
[ 604.478493] -> #1 (&fs_info->cleanup_work_sem){.+.+..}:
[ 604.529313] [<ffffffff810b2c82>] lock_acquire+0xa2/0x140
[ 604.559621] [<ffffffff81632b69>] down_read+0x39/0x4e
[ 604.589382] [<ffffffffa004db98>] btrfs_lookup_dentry+0x218/0x550 [btrfs]
[ 604.596161] btrfs: unlinked 1 orphans
[ 604.675002] [<ffffffffa006aadd>] create_subvol+0x62d/0x690 [btrfs]
[ 604.708859] [<ffffffffa006d666>] btrfs_mksubvol.isra.52+0x346/0x3a0 [btrfs]
[ 604.772466] [<ffffffffa006d7f2>] btrfs_ioctl_snap_create_transid+0x132/0x190 [btrfs]
[ 604.842245] [<ffffffffa006d8ae>] btrfs_ioctl_snap_create+0x5e/0x80 [btrfs]
[ 604.912852] [<ffffffffa00708ae>] btrfs_ioctl+0x138e/0x1990 [btrfs]
[ 604.951888] [<ffffffff8118e9b8>] do_vfs_ioctl+0x98/0x560
[ 604.989961] [<ffffffff8118ef11>] sys_ioctl+0x91/0xa0
[ 605.026628] [<ffffffff8163d569>] system_call_fastpath+0x16/0x1b
[ 605.064404]
[ 605.064404] -> #0 (sb_internal#2){.+.+..}:
[ 605.126832] [<ffffffff810b25e8>] __lock_acquire+0x1ac8/0x1b90
[ 605.163671] [<ffffffff810b2c82>] lock_acquire+0xa2/0x140
[ 605.200228] [<ffffffff8117dac6>] __sb_start_write+0xc6/0x1b0
[ 605.236818] [<ffffffffa0042b84>] start_transaction+0x124/0x430 [btrfs]
[ 605.274029] [<ffffffffa00431a3>] btrfs_start_transaction+0x13/0x20 [btrfs]
[ 605.340520] [<ffffffffa004ccfa>] btrfs_evict_inode+0x19a/0x330 [btrfs]
[ 605.378720] [<ffffffff811972c8>] evict+0xb8/0x1c0
[ 605.416057] [<ffffffff811974d5>] iput+0x105/0x210
[ 605.452373] [<ffffffffa0048082>] btrfs_run_delayed_iputs+0xf2/0x130 [btrfs]
[ 605.521627] [<ffffffffa003b5e1>] cleaner_kthread+0xa1/0x120 [btrfs]
[ 605.560520] [<ffffffff810791ee>] kthread+0xae/0xc0
[ 605.598094] [<ffffffff8163e744>] kernel_thread_helper+0x4/0x10
[ 605.636499]
[ 605.636499] other info that might help us debug this:
[ 605.636499]
[ 605.736504] Possible unsafe locking scenario:
[ 605.736504]
[ 605.801931] CPU0 CPU1
[ 605.835126] ---- ----
[ 605.867093] lock(&fs_info->cleanup_work_sem);
[ 605.898594] lock(sb_internal#2);
[ 605.931954] lock(&fs_info->cleanup_work_sem);
[ 605.965359] lock(sb_internal#2);
[ 605.994758]
[ 605.994758] *** DEADLOCK ***
[ 605.994758]
[ 606.075281] 2 locks held by btrfs-cleaner/6669:
[ 606.104528] #0: (&fs_info->cleaner_mutex){+.+...}, at: [<ffffffffa003b5d5>] cleaner_kthread+0x95/0x120 [btrfs]
[ 606.165626] #1: (&fs_info->cleanup_work_sem){.+.+..}, at: [<ffffffffa0048002>] btrfs_run_delayed_iputs+0x72/0x130 [btrfs]
[ 606.231297]
[ 606.231297] stack backtrace:
[ 606.287723] Pid: 6669, comm: btrfs-cleaner Not tainted 3.6.0-rc2-ceph-00144-g463b030 #1
[ 606.347823] Call Trace:
[ 606.376184] [<ffffffff8162a77c>] print_circular_bug+0x1fb/0x20c
[ 606.409243] [<ffffffff810b25e8>] __lock_acquire+0x1ac8/0x1b90
[ 606.441343] [<ffffffffa0042b84>] ? start_transaction+0x124/0x430 [btrfs]
[ 606.474583] [<ffffffff810b2c82>] lock_acquire+0xa2/0x140
[ 606.505934] [<ffffffffa0042b84>] ? start_transaction+0x124/0x430 [btrfs]
[ 606.539429] [<ffffffff8132babd>] ? do_raw_spin_unlock+0x5d/0xb0
[ 606.571719] [<ffffffff8117dac6>] __sb_start_write+0xc6/0x1b0
[ 606.603498] [<ffffffffa0042b84>] ? start_transaction+0x124/0x430 [btrfs]
[ 606.637405] [<ffffffffa0042b84>] ? start_transaction+0x124/0x430 [btrfs]
[ 606.670165] [<ffffffff81172e75>] ? kmem_cache_alloc+0xb5/0x160
[ 606.702144] [<ffffffffa0042b84>] start_transaction+0x124/0x430 [btrfs]
[ 606.735562] [<ffffffffa00256a6>] ? block_rsv_add_bytes+0x56/0x80 [btrfs]
[ 606.769861] [<ffffffffa00431a3>] btrfs_start_transaction+0x13/0x20 [btrfs]
[ 606.804575] [<ffffffffa004ccfa>] btrfs_evict_inode+0x19a/0x330 [btrfs]
[ 606.838756] [<ffffffff81634c6b>] ? _raw_spin_unlock+0x2b/0x40
[ 606.872010] [<ffffffff811972c8>] evict+0xb8/0x1c0
[ 606.903800] [<ffffffff811974d5>] iput+0x105/0x210
[ 606.935416] [<ffffffffa0048082>] btrfs_run_delayed_iputs+0xf2/0x130 [btrfs]
[ 606.970510] [<ffffffffa003b5d5>] ? cleaner_kthread+0x95/0x120 [btrfs]
[ 607.005648] [<ffffffffa003b5e1>] cleaner_kthread+0xa1/0x120 [btrfs]
[ 607.040724] [<ffffffffa003b540>] ? btrfs_destroy_delayed_refs.isra.102+0x220/0x220 [btrfs]
[ 607.104740] [<ffffffff810791ee>] kthread+0xae/0xc0
[ 607.137119] [<ffffffff810b379d>] ? trace_hardirqs_on+0xd/0x10
[ 607.169797] [<ffffffff8163e744>] kernel_thread_helper+0x4/0x10
[ 607.202472] [<ffffffff81635430>] ? retint_restore_args+0x13/0x13
[ 607.235884] [<ffffffff81079140>] ? flush_kthread_work+0x1a0/0x1a0
[ 607.268731] [<ffffffff8163e740>] ? gs_change+0x13/0x13
Signed-off-by: Sage Weil <sage@inktank.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8cb272c..073af07 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2118,7 +2118,6 @@
if (empty)
return;
- down_read(&root->fs_info->cleanup_work_sem);
spin_lock(&fs_info->delayed_iput_lock);
list_splice_init(&fs_info->delayed_iputs, &list);
spin_unlock(&fs_info->delayed_iput_lock);
@@ -2129,7 +2128,6 @@
iput(delayed->inode);
kfree(delayed);
}
- up_read(&root->fs_info->cleanup_work_sem);
}
enum btrfs_orphan_cleanup_state {