@@ -41,6 +41,7 @@ void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
*/
if (eb->lock_nested && current->pid == eb->lock_owner)
return;
+ trace_printk("eb %p rw %d\n", eb, rw);
if (rw == BTRFS_WRITE_LOCK) {
if (atomic_read(&eb->blocking_writers) == 0) {
WARN_ON(atomic_read(&eb->spinning_writers) != 1);
@@ -73,6 +74,7 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
if (eb->lock_nested && current->pid == eb->lock_owner)
return;
+ trace_printk("eb %p rw %d\n", eb, rw);
if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
BUG_ON(atomic_read(&eb->blocking_writers) != 1);
write_lock(&eb->lock);
With lockdep enabled I managed to trigger the following lockdep splat: | ============================================= | [ INFO: possible recursive locking detected ] | 4.9.0-rt0 #804 Tainted: G W | --------------------------------------------- | kworker/u16:4/154 is trying to acquire lock: | (btrfs-fs-00){+.+...}, at: [<ffffffff8136f0e1>] btrfs_clear_lock_blocking_rw+0x71/0x120 | | but task is already holding lock: | (btrfs-fs-00){+.+...}, at: [<ffffffff8136f0e1>] btrfs_clear_lock_blocking_rw+0x71/0x120 | | other info that might help us debug this: | Possible unsafe locking scenario: | | CPU0 | ---- | lock(btrfs-fs-00); | lock(btrfs-fs-00); | | *** DEADLOCK *** | | May be due to missing lock nesting notation | | 6 locks held by kworker/u16:4/154: | #0: ("%s-%s""btrfs", name){.+.+.+}, at: [<ffffffff8108af13>] process_one_work+0x1f3/0x7b0 | #1: ((&work->normal_work)){+.+.+.}, at: [<ffffffff8108af13>] process_one_work+0x1f3/0x7b0 | #2: (sb_internal){.+.+..}, at: [<ffffffff8132f7a1>] start_transaction+0x2f1/0x590 | #3: (btrfs-fs-02){+.+...}, at: [<ffffffff8136f0e1>] btrfs_clear_lock_blocking_rw+0x71/0x120 | #4: (btrfs-fs-01){+.+...}, at: [<ffffffff8136f0e1>] btrfs_clear_lock_blocking_rw+0x71/0x120 | #5: (btrfs-fs-00){+.+...}, at: [<ffffffff8136f0e1>] btrfs_clear_lock_blocking_rw+0x71/0x120 | | stack backtrace: | CPU: 1 PID: 154 Comm: kworker/u16:4 Tainted: G W 4.9.0-rt1+ #804 | Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014 | Workqueue: btrfs-delalloc btrfs_delalloc_helper | ffffc9000123b7d0 ffffffff8141a2a5 ffffffff829d6db0 ffffffff829d6db0 | ffffc9000123b890 ffffffff810c19dd 00000000000002fe 0000000000000006 | 000000003c272f80 ffffffff82308200 ce68145f590e60eb ffff880039c108c0 | Call Trace: | [<ffffffff8141a2a5>] dump_stack+0x86/0xc1 | [<ffffffff810c19dd>] __lock_acquire+0x6dd/0x11d0 | [<ffffffff810c2956>] lock_acquire+0x116/0x240 | [<ffffffff818e0ed5>] rt_read_lock+0x45/0x60 | [<ffffffff8136f0e1>] btrfs_clear_lock_blocking_rw+0x71/0x120 | [<ffffffff812fec14>] btrfs_clear_path_blocking+0x94/0xb0 | [<ffffffff8130706f>] btrfs_next_old_leaf+0x3df/0x420 | [<ffffffff813070bb>] btrfs_next_leaf+0xb/0x10 | [<ffffffff81344eeb>] __btrfs_drop_extents+0x1cb/0xd50 | [<ffffffff81336161>] cow_file_range_inline+0x191/0x6c0 | [<ffffffff81338364>] compress_file_range.constprop.68+0x314/0x710 | [<ffffffff81338790>] async_cow_start+0x30/0x50 | [<ffffffff813644dd>] btrfs_scrubparity_helper+0xfd/0x620 | [<ffffffff81364b39>] btrfs_delalloc_helper+0x9/0x10 | [<ffffffff8108af8e>] process_one_work+0x26e/0x7b0 | [<ffffffff8108b516>] worker_thread+0x46/0x560 | [<ffffffff81091c4e>] kthread+0xee/0x110 | [<ffffffff818e166a>] ret_from_fork+0x2a/0x40 I can trigger it on -RT but it won't show up on a vanilla kernel. I don't see obvious difference here (between RT and !RT). We do have more preemption points and a spin_lock() does not disable preemption (so any assumption on spin_lock() disabling preemption will fail). With all btrfs events enabled, this did not trigger. With the following patch I manage to collect this (the last few lines from the kworker): # _-----=> irqs-off # / _----=> need-resched # |/ _-----=> need-resched_lazy # || / _---=> hardirq/softirq # ||| / _--=> preempt-depth # |||| / _-=> preempt-lazy-depth # ||||| / _-=> migrate-disable # |||||| / delay # TASK-PID CPU# ||||||| TIMESTAMP FUNCTION # | | | ||||||| | | kworker/u16:4-154 [001] .....11 60.632361: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 1 kworker/u16:4-154 [001] ....... 60.632362: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 3 kworker/u16:4-154 [001] .....11 60.632366: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 1 kworker/u16:4-154 [001] ....... 60.632367: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 3 kworker/u16:4-154 [001] .....11 60.632367: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 1 kworker/u16:4-154 [001] ....... 60.632368: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 3 kworker/u16:4-154 [001] ....... 60.632369: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 3 kworker/u16:4-154 [001] .....12 60.632371: btrfs_set_lock_blocking_rw: eb ffff880039ebb000 rw 1 kworker/u16:4-154 [001] .....11 60.632372: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 1 kworker/u16:4-154 [001] ....... 60.632372: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 3 kworker/u16:4-154 [001] .....11 60.632373: btrfs_clear_lock_blocking_rw: eb ffff880039ebb000 rw 3 kworker/u16:4-154 [001] .....12 60.632376: btrfs_set_lock_blocking_rw: eb ffff880039104000 rw 1 kworker/u16:4-154 [001] .....11 60.632377: btrfs_set_lock_blocking_rw: eb ffff880039ebb000 rw 1 kworker/u16:4-154 [001] ....... 60.632377: btrfs_clear_lock_blocking_rw: eb ffff880039ebb000 rw 3 kworker/u16:4-154 [001] .....11 60.632378: btrfs_clear_lock_blocking_rw: eb ffff880039104000 rw 3 kworker/u16:4-154 [001] .....12 60.632379: btrfs_set_lock_blocking_rw: eb ffff880039104000 rw 1 kworker/u16:4-154 [001] .....11 60.632380: btrfs_set_lock_blocking_rw: eb ffff880039ebb000 rw 1 kworker/u16:4-154 [001] .....11 60.632384: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 2 kworker/u16:4-154 [001] ....... 60.632384: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 4 kworker/u16:4-154 [001] .....12 60.632386: btrfs_set_lock_blocking_rw: eb ffff880039ebb000 rw 2 kworker/u16:4-154 [001] .....11 60.632387: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 2 kworker/u16:4-154 [001] ....... 60.632392: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 4 kworker/u16:4-154 [001] .....11 60.632392: btrfs_clear_lock_blocking_rw: eb ffff880039ebb000 rw 4 kworker/u16:4-154 [001] .....13 60.632395: btrfs_set_lock_blocking_rw: eb ffff880039104000 rw 2 kworker/u16:4-154 [001] .....12 60.632395: btrfs_set_lock_blocking_rw: eb ffff880039ebb000 rw 2 kworker/u16:4-154 [001] .....11 60.632396: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 2 kworker/u16:4-154 [001] ....... 60.632399: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 4 kworker/u16:4-154 [001] .....11 60.632404: btrfs_clear_lock_blocking_rw: eb ffff880039ebb000 rw 4 kworker/u16:4-154 [001] .....12 60.632404: btrfs_clear_lock_blocking_rw: eb ffff880039104000 rw 4 kworker/u16:4-154 [001] .....13 60.632406: btrfs_set_lock_blocking_rw: eb ffff880039104000 rw 2 kworker/u16:4-154 [001] .....12 60.632407: btrfs_set_lock_blocking_rw: eb ffff880039ebb000 rw 2 kworker/u16:4-154 [001] .....11 60.632407: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 2 kworker/u16:4-154 [001] .....11 60.632601: btrfs_set_lock_blocking_rw: eb ffff880039763c00 rw 2 kworker/u16:4-154 [001] ....... 60.632601: btrfs_set_lock_blocking_rw: eb ffff880039104000 rw 4 kworker/u16:4-154 [001] ....... 60.632602: btrfs_set_lock_blocking_rw: eb ffff880039ebb000 rw 4 kworker/u16:4-154 [001] ....... 60.632602: btrfs_set_lock_blocking_rw: eb ffff880039ebac00 rw 4 kworker/u16:4-154 [001] ....... 60.632602: btrfs_clear_lock_blocking_rw: eb ffff880039ebac00 rw 4 kworker/u16:4-154 [001] .....11 60.632610: btrfs_clear_lock_blocking_rw: eb ffff880039ebb000 rw 4 kworker/u16:4-154 [001] .....12 60.632611: btrfs_clear_lock_blocking_rw: eb ffff880039104000 rw 4 kworker/u16:4-154 [001] .....13 60.632612: btrfs_clear_lock_blocking_rw: eb ffff880039763c00 rw 4 Could this be a wrong / missing lockdep annotation? Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html