[PATCH 5.1 24/85] btrfs: correct zstd workspace manager lock to use spin_lock_bh()

From: Greg Kroah-Hartman
Date: Fri Jun 07 2019 - 11:54:15 EST

From: Dennis Zhou <dennis@xxxxxxxxxx>

commit fee13fe96529523a709d1fff487f14a5e0d56d34 upstream.

The btrfs zstd workspace manager uses a background timer to reclaim not
recently used workspaces. I used spin_lock() from this context which
should have been caught with lockdep, but was not. This deadlock was
reported in bugzilla. The fix is to switch the zstd wsm lock to use
spin_lock_bh() from the softirq context.

This happened quite relibably on ppc64, unlike on other architectures.

[ 313.402874] ================================
[ 313.402875] WARNING: inconsistent lock state
[ 313.402879] 5.1.0-rc7 #1 Not tainted
[ 313.402880] --------------------------------
[ 313.402882] inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
[ 313.402885] swapper/5/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
[ 313.402888] 0000000080d1120c (&(&wsm.lock)->rlock){+.?.}, at: .zstd_reclaim_timer_fn+0x40/0x230
[ 313.402895] {SOFTIRQ-ON-W} state was registered at:
[ 313.402899] .lock_acquire+0xd0/0x240
[ 313.402903] ._raw_spin_lock+0x34/0x60
[ 313.402906] .zstd_get_workspace+0xd0/0x360
[ 313.402908] .end_compressed_bio_read+0x3b8/0x540
[ 313.402911] .bio_endio+0x174/0x2c0
[ 313.402914] .end_workqueue_fn+0x4c/0x70
[ 313.402917] .normal_work_helper+0x138/0x7e0
[ 313.402920] .process_one_work+0x324/0x790
[ 313.402922] .worker_thread+0x68/0x570
[ 313.402925] .kthread+0x19c/0x1b0
[ 313.402928] .ret_from_kernel_thread+0x58/0x78
[ 313.402930] irq event stamp: 2629216
[ 313.402933] hardirqs last enabled at (2629216): [<c0000000009da738>] ._raw_spin_unlock_irq+0x38/0x60
[ 313.402936] hardirqs last disabled at (2629215): [<c0000000009da4c4>] ._raw_spin_lock_irq+0x24/0x70
[ 313.402939] softirqs last enabled at (2629212): [<c0000000000af9fc>] .irq_enter+0x8c/0xd0
[ 313.402942] softirqs last disabled at (2629213): [<c0000000000afb58>] .irq_exit+0x118/0x170
[ 313.402944]
other info that might help us debug this:
[ 313.402945] Possible unsafe locking scenario:

[ 313.402947] CPU0
[ 313.402948] ----
[ 313.402949] lock(&(&wsm.lock)->rlock);
[ 313.402951] <Interrupt>
[ 313.402952] lock(&(&wsm.lock)->rlock);
[ 313.402954]
*** DEADLOCK ***

[ 313.402957] 1 lock held by swapper/5/0:
[ 313.402958] #0: 000000004b612042 ((&wsm.timer)){+.-.}, at: .call_timer_fn+0x0/0x3c0
[ 313.402963]
stack backtrace:
[ 313.402967] CPU: 5 PID: 0 Comm: swapper/5 Not tainted 5.1.0-rc7 #1
[ 313.402968] Call Trace:
[ 313.402972] [c0000007fa262e70] [c0000000009b3294] .dump_stack+0xe0/0x15c (unreliable)
[ 313.402975] [c0000007fa262f10] [c000000000125548] .print_usage_bug+0x348/0x390
[ 313.402978] [c0000007fa262fd0] [c000000000125cb4] .mark_lock+0x724/0x930
[ 313.402981] [c0000007fa263080] [c000000000126c20] .__lock_acquire+0xc90/0x16a0
[ 313.402984] [c0000007fa2631b0] [c000000000128040] .lock_acquire+0xd0/0x240
[ 313.402987] [c0000007fa263280] [c0000000009da2b4] ._raw_spin_lock+0x34/0x60
[ 313.402990] [c0000007fa263300] [c00000000054b0b0] .zstd_reclaim_timer_fn+0x40/0x230
[ 313.402993] [c0000007fa2633d0] [c000000000158b38] .call_timer_fn+0xc8/0x3c0
[ 313.402996] [c0000007fa2634a0] [c000000000158f74] .expire_timers+0x144/0x260
[ 313.402999] [c0000007fa263550] [c000000000159178] .run_timer_softirq+0xe8/0x230
[ 313.403002] [c0000007fa263680] [c0000000009db288] .__do_softirq+0x188/0x5d4
[ 313.403004] [c0000007fa263790] [c0000000000afb58] .irq_exit+0x118/0x170
[ 313.403008] [c0000007fa263800] [c000000000028d88] .timer_interrupt+0x158/0x430
[ 313.403012] [c0000007fa2638b0] [c0000000000091d4] decrementer_common+0x134/0x140
[ 313.403017] --- interrupt: 901 at replay_interrupt_return+0x0/0x4
LR = .arch_local_irq_restore.part.0+0x68/0x80
[ 313.403020] [c0000007fa263bb0] [c00000000001a3ac] .arch_local_irq_restore.part.0+0x2c/0x80 (unreliable)
[ 313.403024] [c0000007fa263c30] [c0000000007bbbcc] .cpuidle_enter_state+0xec/0x670
[ 313.403027] [c0000007fa263d00] [c0000000000f5130] .call_cpuidle+0x40/0x90
[ 313.403031] [c0000007fa263d70] [c0000000000f554c] .do_idle+0x2dc/0x3a0
[ 313.403034] [c0000007fa263e30] [c0000000000f59ac] .cpu_startup_entry+0x2c/0x30
[ 313.403037] [c0000007fa263ea0] [c000000000045674] .start_secondary+0x644/0x650
[ 313.403041] [c0000007fa263f90] [c00000000000ad5c] start_secondary_prolog+0x10/0x14

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203517
Fixes: 3f93aef535c8 ("btrfs: add zstd compression level support")
CC: stable@xxxxxxxxxxxxxxx # 5.1+
Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/btrfs/zstd.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

--- a/fs/btrfs/zstd.c
+++ b/fs/btrfs/zstd.c
@@ -102,10 +102,10 @@ static void zstd_reclaim_timer_fn(struct
unsigned long reclaim_threshold = jiffies - ZSTD_BTRFS_RECLAIM_JIFFIES;
struct list_head *pos, *next;

- spin_lock(&wsm.lock);
+ spin_lock_bh(&wsm.lock);

if (list_empty(&wsm.lru_list)) {
- spin_unlock(&wsm.lock);
+ spin_unlock_bh(&wsm.lock);
return;
}

@@ -134,7 +134,7 @@ static void zstd_reclaim_timer_fn(struct
if (!list_empty(&wsm.lru_list))
mod_timer(&wsm.timer, jiffies + ZSTD_BTRFS_RECLAIM_JIFFIES);

- spin_unlock(&wsm.lock);
+ spin_unlock_bh(&wsm.lock);
}

/*
@@ -195,7 +195,7 @@ static void zstd_cleanup_workspace_manag
struct workspace *workspace;
int i;

- spin_lock(&wsm.lock);
+ spin_lock_bh(&wsm.lock);
for (i = 0; i < ZSTD_BTRFS_MAX_LEVEL; i++) {
while (!list_empty(&wsm.idle_ws[i])) {
workspace = container_of(wsm.idle_ws[i].next,
@@ -205,7 +205,7 @@ static void zstd_cleanup_workspace_manag
wsm.ops->free_workspace(&workspace->list);
}
}
- spin_unlock(&wsm.lock);
+ spin_unlock_bh(&wsm.lock);

del_timer_sync(&wsm.timer);
}
@@ -227,7 +227,7 @@ static struct list_head *zstd_find_works
struct workspace *workspace;
int i = level - 1;

- spin_lock(&wsm.lock);
+ spin_lock_bh(&wsm.lock);
for_each_set_bit_from(i, &wsm.active_map, ZSTD_BTRFS_MAX_LEVEL) {
if (!list_empty(&wsm.idle_ws[i])) {
ws = wsm.idle_ws[i].next;
@@ -239,11 +239,11 @@ static struct list_head *zstd_find_works
list_del(&workspace->lru_list);
if (list_empty(&wsm.idle_ws[i]))
clear_bit(i, &wsm.active_map);
- spin_unlock(&wsm.lock);
+ spin_unlock_bh(&wsm.lock);
return ws;
}
}
- spin_unlock(&wsm.lock);
+ spin_unlock_bh(&wsm.lock);

return NULL;
}
@@ -302,7 +302,7 @@ static void zstd_put_workspace(struct li
{
struct workspace *workspace = list_to_workspace(ws);

- spin_lock(&wsm.lock);
+ spin_lock_bh(&wsm.lock);

/* A node is only taken off the lru if we are the corresponding level */
if (workspace->req_level == workspace->level) {
@@ -322,7 +322,7 @@ static void zstd_put_workspace(struct li
list_add(&workspace->list, &wsm.idle_ws[workspace->level - 1]);
workspace->req_level = 0;

- spin_unlock(&wsm.lock);
+ spin_unlock_bh(&wsm.lock);

if (workspace->level == ZSTD_BTRFS_MAX_LEVEL)
cond_wake_up(&wsm.wait);