[PATCH AUTOSEL 5.2 192/249] bcache: fix return value error in bch_journal_read()

[PATCH AUTOSEL 5.2 192/249] bcache: fix return value error in bch_journal_read()

[Sasha Levin]

From: Coly Li <colyli@suse.de>

[ Upstream commit 0ae49cb7aa005ed18fe8f4d6ccf73019b78ac7b2 ]

When everything is OK in bch_journal_read(), finally the return value
is returned by,
	return ret;
which assumes ret will be 0 here. This assumption is wrong when all
journal buckets as are full and filled with valid journal entries. In
such cache the last location referencess read_bucket() sets 'ret' to
1, which means new jset added into jset list. The jset list is list
'journal' in caller run_cache_set().

Return 1 to run_cache_set() means something wrong and the cache set
won't start, but indeed everything is OK.

This patch changes the line at end of bch_journal_read() to directly
return 0 since everything if verything is good. Then a bogus error
is fixed.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/journal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index 12dae9348147..4e5fc05720fc 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -268,7 +268,7 @@ int bch_journal_read(struct cache_set *c, struct list_head *list)
 					    struct journal_replay,
 					    list)->j.seq;
 
-	return ret;
+	return 0;
 #undef read_bucket
 }
 
-- 
2.20.1

[PATCH AUTOSEL 5.2 193/249] bcache: check CACHE_SET_IO_DISABLE in allocator code

[Sasha Levin]

From: Coly Li <colyli@suse.de>

[ Upstream commit e775339e1ae1205b47d94881db124c11385e597c ]

If CACHE_SET_IO_DISABLE of a cache set flag is set by too many I/O
errors, currently allocator routines can still continue allocate
space which may introduce inconsistent metadata state.

This patch checkes CACHE_SET_IO_DISABLE bit in following allocator
routines,
- bch_bucket_alloc()
- __bch_bucket_alloc_set()
Once CACHE_SET_IO_DISABLE is set on cache set, the allocator routines
may reject allocation request earlier to avoid potential inconsistent
metadata.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/alloc.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
index f8986effcb50..6f776823b9ba 100644
--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -393,6 +393,11 @@ long bch_bucket_alloc(struct cache *ca, unsigned int reserve, bool wait)
 	struct bucket *b;
 	long r;
 
+
+	/* No allocation if CACHE_SET_IO_DISABLE bit is set */
+	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &ca->set->flags)))
+		return -1;
+
 	/* fastpath */
 	if (fifo_pop(&ca->free[RESERVE_NONE], r) ||
 	    fifo_pop(&ca->free[reserve], r))
@@ -484,6 +489,10 @@ int __bch_bucket_alloc_set(struct cache_set *c, unsigned int reserve,
 {
 	int i;
 
+	/* No allocation if CACHE_SET_IO_DISABLE bit is set */
+	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags)))
+		return -1;
+
 	lockdep_assert_held(&c->bucket_lock);
 	BUG_ON(!n || n > c->caches_loaded || n > MAX_CACHES_PER_SET);
 
-- 
2.20.1

[PATCH AUTOSEL 5.2 194/249] bcache: check CACHE_SET_IO_DISABLE bit in bch_journal()

[Sasha Levin]

From: Coly Li <colyli@suse.de>

[ Upstream commit 383ff2183ad16a8842d1fbd9dd3e1cbd66813e64 ]

When too many I/O errors happen on cache set and CACHE_SET_IO_DISABLE
bit is set, bch_journal() may continue to work because the journaling
bkey might be still in write set yet. The caller of bch_journal() may
believe the journal still work but the truth is in-memory journal write
set won't be written into cache device any more. This behavior may
introduce potential inconsistent metadata status.

This patch checks CACHE_SET_IO_DISABLE bit at the head of bch_journal(),
if the bit is set, bch_journal() returns NULL immediately to notice
caller to know journal does not work.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/journal.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index 4e5fc05720fc..54f8886b6177 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -811,6 +811,10 @@ atomic_t *bch_journal(struct cache_set *c,
 	struct journal_write *w;
 	atomic_t *ret;
 
+	/* No journaling if CACHE_SET_IO_DISABLE set already */
+	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags)))
+		return NULL;
+
 	if (!CACHE_SYNC(&c->sb))
 		return NULL;
 
-- 
2.20.1

[PATCH AUTOSEL 5.2 195/249] bcache: acquire bch_register_lock later in cached_dev_free()

[Sasha Levin]

From: Coly Li <colyli@suse.de>

[ Upstream commit 80265d8dfd77792e133793cef44a21323aac2908 ]

When enable lockdep engine, a lockdep warning can be observed when
reboot or shutdown system,

[ 3142.764557][    T1] bcache: bcache_reboot() Stopping all devices:
[ 3142.776265][ T2649]
[ 3142.777159][ T2649] ======================================================
[ 3142.780039][ T2649] WARNING: possible circular locking dependency detected
[ 3142.782869][ T2649] 5.2.0-rc4-lp151.20-default+ #1 Tainted: G        W
[ 3142.785684][ T2649] ------------------------------------------------------
[ 3142.788479][ T2649] kworker/3:67/2649 is trying to acquire lock:
[ 3142.790738][ T2649] 00000000aaf02291 ((wq_completion)bcache_writeback_wq){+.+.}, at: flush_workqueue+0x87/0x4c0
[ 3142.794678][ T2649]
[ 3142.794678][ T2649] but task is already holding lock:
[ 3142.797402][ T2649] 000000004fcf89c5 (&bch_register_lock){+.+.}, at: cached_dev_free+0x17/0x120 [bcache]
[ 3142.801462][ T2649]
[ 3142.801462][ T2649] which lock already depends on the new lock.
[ 3142.801462][ T2649]
[ 3142.805277][ T2649]
[ 3142.805277][ T2649] the existing dependency chain (in reverse order) is:
[ 3142.808902][ T2649]
[ 3142.808902][ T2649] -> #2 (&bch_register_lock){+.+.}:
[ 3142.812396][ T2649]        __mutex_lock+0x7a/0x9d0
[ 3142.814184][ T2649]        cached_dev_free+0x17/0x120 [bcache]
[ 3142.816415][ T2649]        process_one_work+0x2a4/0x640
[ 3142.818413][ T2649]        worker_thread+0x39/0x3f0
[ 3142.820276][ T2649]        kthread+0x125/0x140
[ 3142.822061][ T2649]        ret_from_fork+0x3a/0x50
[ 3142.823965][ T2649]
[ 3142.823965][ T2649] -> #1 ((work_completion)(&cl->work)#2){+.+.}:
[ 3142.827244][ T2649]        process_one_work+0x277/0x640
[ 3142.829160][ T2649]        worker_thread+0x39/0x3f0
[ 3142.830958][ T2649]        kthread+0x125/0x140
[ 3142.832674][ T2649]        ret_from_fork+0x3a/0x50
[ 3142.834915][ T2649]
[ 3142.834915][ T2649] -> #0 ((wq_completion)bcache_writeback_wq){+.+.}:
[ 3142.838121][ T2649]        lock_acquire+0xb4/0x1c0
[ 3142.840025][ T2649]        flush_workqueue+0xae/0x4c0
[ 3142.842035][ T2649]        drain_workqueue+0xa9/0x180
[ 3142.844042][ T2649]        destroy_workqueue+0x17/0x250
[ 3142.846142][ T2649]        cached_dev_free+0x52/0x120 [bcache]
[ 3142.848530][ T2649]        process_one_work+0x2a4/0x640
[ 3142.850663][ T2649]        worker_thread+0x39/0x3f0
[ 3142.852464][ T2649]        kthread+0x125/0x140
[ 3142.854106][ T2649]        ret_from_fork+0x3a/0x50
[ 3142.855880][ T2649]
[ 3142.855880][ T2649] other info that might help us debug this:
[ 3142.855880][ T2649]
[ 3142.859663][ T2649] Chain exists of:
[ 3142.859663][ T2649]   (wq_completion)bcache_writeback_wq --> (work_completion)(&cl->work)#2 --> &bch_register_lock
[ 3142.859663][ T2649]
[ 3142.865424][ T2649]  Possible unsafe locking scenario:
[ 3142.865424][ T2649]
[ 3142.868022][ T2649]        CPU0                    CPU1
[ 3142.869885][ T2649]        ----                    ----
[ 3142.871751][ T2649]   lock(&bch_register_lock);
[ 3142.873379][ T2649]                                lock((work_completion)(&cl->work)#2);
[ 3142.876399][ T2649]                                lock(&bch_register_lock);
[ 3142.879727][ T2649]   lock((wq_completion)bcache_writeback_wq);
[ 3142.882064][ T2649]
[ 3142.882064][ T2649]  *** DEADLOCK ***
[ 3142.882064][ T2649]
[ 3142.885060][ T2649] 3 locks held by kworker/3:67/2649:
[ 3142.887245][ T2649]  #0: 00000000e774cdd0 ((wq_completion)events){+.+.}, at: process_one_work+0x21e/0x640
[ 3142.890815][ T2649]  #1: 00000000f7df89da ((work_completion)(&cl->work)#2){+.+.}, at: process_one_work+0x21e/0x640
[ 3142.894884][ T2649]  #2: 000000004fcf89c5 (&bch_register_lock){+.+.}, at: cached_dev_free+0x17/0x120 [bcache]
[ 3142.898797][ T2649]
[ 3142.898797][ T2649] stack backtrace:
[ 3142.900961][ T2649] CPU: 3 PID: 2649 Comm: kworker/3:67 Tainted: G        W         5.2.0-rc4-lp151.20-default+ #1
[ 3142.904789][ T2649] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/13/2018
[ 3142.909168][ T2649] Workqueue: events cached_dev_free [bcache]
[ 3142.911422][ T2649] Call Trace:
[ 3142.912656][ T2649]  dump_stack+0x85/0xcb
[ 3142.914181][ T2649]  print_circular_bug+0x19a/0x1f0
[ 3142.916193][ T2649]  __lock_acquire+0x16cd/0x1850
[ 3142.917936][ T2649]  ? __lock_acquire+0x6a8/0x1850
[ 3142.919704][ T2649]  ? lock_acquire+0xb4/0x1c0
[ 3142.921335][ T2649]  ? find_held_lock+0x34/0xa0
[ 3142.923052][ T2649]  lock_acquire+0xb4/0x1c0
[ 3142.924635][ T2649]  ? flush_workqueue+0x87/0x4c0
[ 3142.926375][ T2649]  flush_workqueue+0xae/0x4c0
[ 3142.928047][ T2649]  ? flush_workqueue+0x87/0x4c0
[ 3142.929824][ T2649]  ? drain_workqueue+0xa9/0x180
[ 3142.931686][ T2649]  drain_workqueue+0xa9/0x180
[ 3142.933534][ T2649]  destroy_workqueue+0x17/0x250
[ 3142.935787][ T2649]  cached_dev_free+0x52/0x120 [bcache]
[ 3142.937795][ T2649]  process_one_work+0x2a4/0x640
[ 3142.939803][ T2649]  worker_thread+0x39/0x3f0
[ 3142.941487][ T2649]  ? process_one_work+0x640/0x640
[ 3142.943389][ T2649]  kthread+0x125/0x140
[ 3142.944894][ T2649]  ? kthread_create_worker_on_cpu+0x70/0x70
[ 3142.947744][ T2649]  ret_from_fork+0x3a/0x50
[ 3142.970358][ T2649] bcache: bcache_device_free() bcache0 stopped

Here is how the deadlock happens.
1) bcache_reboot() calls bcache_device_stop(), then inside
   bcache_device_stop() BCACHE_DEV_CLOSING bit is set on d->flags.
   Then closure_queue(&d->cl) is called to invoke cached_dev_flush().
2) In cached_dev_flush(), cached_dev_free() is called by continu_at().
3) In cached_dev_free(), when stopping the writeback kthread of the
   cached device by kthread_stop(), dc->writeback_thread will be waken
   up to quite the kthread while-loop, then cached_dev_put() is called
   in bch_writeback_thread().
4) Calling cached_dev_put() in writeback kthread may drop dc->count to
   0, then dc->detach kworker is scheduled, which is initialized as
   cached_dev_detach_finish().
5) Inside cached_dev_detach_finish(), the last line of code is to call
   closure_put(&dc->disk.cl), which drops the last reference counter of
   closrure dc->disk.cl, then the callback cached_dev_flush() gets
   called.
Now cached_dev_flush() is called for second time in the code path, the
first time is in step 2). And again bch_register_lock will be acquired
again, and a A-A lock (lockdep terminology) is happening.

The root cause of the above A-A lock is in cached_dev_free(), mutex
bch_register_lock is held before stopping writeback kthread and other
kworkers. Fortunately now we have variable 'bcache_is_reboot', which may
prevent device registration or unregistration during reboot/shutdown
time, so it is unncessary to hold bch_register_lock such early now.

This is how this patch fixes the reboot/shutdown time A-A lock issue:
After moving mutex_lock(&bch_register_lock) to a later location where
before atomic_read(&dc->running) in cached_dev_free(), such A-A lock
problem can be solved without any reboot time registration race.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 1b63ac876169..0a25774e175a 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1190,8 +1190,6 @@ static void cached_dev_free(struct closure *cl)
 {
 	struct cached_dev *dc = container_of(cl, struct cached_dev, disk.cl);
 
-	mutex_lock(&bch_register_lock);
-
 	if (test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags))
 		cancel_writeback_rate_update_dwork(dc);
 
@@ -1202,6 +1200,8 @@ static void cached_dev_free(struct closure *cl)
 	if (!IS_ERR_OR_NULL(dc->status_update_thread))
 		kthread_stop(dc->status_update_thread);
 
+	mutex_lock(&bch_register_lock);
+
 	if (atomic_read(&dc->running))
 		bd_unlink_disk_holder(dc->bdev, dc->disk.disk);
 	bcache_device_free(&dc->disk);
-- 
2.20.1

[PATCH AUTOSEL 5.2 196/249] bcache: check c->gc_thread by IS_ERR_OR_NULL in cache_set_flush()

[Sasha Levin]

From: Coly Li <colyli@suse.de>

[ Upstream commit b387e9b58679c60f5b1e4313939bd4878204fc37 ]

When system memory is in heavy pressure, bch_gc_thread_start() from
run_cache_set() may fail due to out of memory. In such condition,
c->gc_thread is assigned to -ENOMEM, not NULL pointer. Then in following
failure code path bch_cache_set_error(), when cache_set_flush() gets
called, the code piece to stop c->gc_thread is broken,
         if (!IS_ERR_OR_NULL(c->gc_thread))
                 kthread_stop(c->gc_thread);

And KASAN catches such NULL pointer deference problem, with the warning
information:

[  561.207881] ==================================================================
[  561.207900] BUG: KASAN: null-ptr-deref in kthread_stop+0x3b/0x440
[  561.207904] Write of size 4 at addr 000000000000001c by task kworker/15:1/313

[  561.207913] CPU: 15 PID: 313 Comm: kworker/15:1 Tainted: G        W         5.0.0-vanilla+ #3
[  561.207916] Hardware name: Lenovo ThinkSystem SR650 -[7X05CTO1WW]-/-[7X05CTO1WW]-, BIOS -[IVE136T-2.10]- 03/22/2019
[  561.207935] Workqueue: events cache_set_flush [bcache]
[  561.207940] Call Trace:
[  561.207948]  dump_stack+0x9a/0xeb
[  561.207955]  ? kthread_stop+0x3b/0x440
[  561.207960]  ? kthread_stop+0x3b/0x440
[  561.207965]  kasan_report+0x176/0x192
[  561.207973]  ? kthread_stop+0x3b/0x440
[  561.207981]  kthread_stop+0x3b/0x440
[  561.207995]  cache_set_flush+0xd4/0x6d0 [bcache]
[  561.208008]  process_one_work+0x856/0x1620
[  561.208015]  ? find_held_lock+0x39/0x1d0
[  561.208028]  ? drain_workqueue+0x380/0x380
[  561.208048]  worker_thread+0x87/0xb80
[  561.208058]  ? __kthread_parkme+0xb6/0x180
[  561.208067]  ? process_one_work+0x1620/0x1620
[  561.208072]  kthread+0x326/0x3e0
[  561.208079]  ? kthread_create_worker_on_cpu+0xc0/0xc0
[  561.208090]  ret_from_fork+0x3a/0x50
[  561.208110] ==================================================================
[  561.208113] Disabling lock debugging due to kernel taint
[  561.208115] irq event stamp: 11800231
[  561.208126] hardirqs last  enabled at (11800231): [<ffffffff83008538>] do_syscall_64+0x18/0x410
[  561.208127] BUG: unable to handle kernel NULL pointer dereference at 000000000000001c
[  561.208129] #PF error: [WRITE]
[  561.312253] hardirqs last disabled at (11800230): [<ffffffff830052ff>] trace_hardirqs_off_thunk+0x1a/0x1c
[  561.312259] softirqs last  enabled at (11799832): [<ffffffff850005c7>] __do_softirq+0x5c7/0x8c3
[  561.405975] PGD 0 P4D 0
[  561.442494] softirqs last disabled at (11799821): [<ffffffff831add2c>] irq_exit+0x1ac/0x1e0
[  561.791359] Oops: 0002 [#1] SMP KASAN NOPTI
[  561.791362] CPU: 15 PID: 313 Comm: kworker/15:1 Tainted: G    B   W         5.0.0-vanilla+ #3
[  561.791363] Hardware name: Lenovo ThinkSystem SR650 -[7X05CTO1WW]-/-[7X05CTO1WW]-, BIOS -[IVE136T-2.10]- 03/22/2019
[  561.791371] Workqueue: events cache_set_flush [bcache]
[  561.791374] RIP: 0010:kthread_stop+0x3b/0x440
[  561.791376] Code: 00 00 65 8b 05 26 d5 e0 7c 89 c0 48 0f a3 05 ec aa df 02 0f 82 dc 02 00 00 4c 8d 63 20 be 04 00 00 00 4c 89 e7 e8 65 c5 53 00 <f0> ff 43 20 48 8d 7b 24 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48
[  561.791377] RSP: 0018:ffff88872fc8fd10 EFLAGS: 00010286
[  561.838895] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  561.838916] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  561.838934] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  561.838948] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  561.838966] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  561.838979] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  561.838996] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  563.067028] RAX: 0000000000000000 RBX: fffffffffffffffc RCX: ffffffff832dd314
[  563.067030] RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000297
[  563.067032] RBP: ffff88872fc8fe88 R08: fffffbfff0b8213d R09: fffffbfff0b8213d
[  563.067034] R10: 0000000000000001 R11: fffffbfff0b8213c R12: 000000000000001c
[  563.408618] R13: ffff88dc61cc0f68 R14: ffff888102b94900 R15: ffff88dc61cc0f68
[  563.408620] FS:  0000000000000000(0000) GS:ffff888f7dc00000(0000) knlGS:0000000000000000
[  563.408622] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  563.408623] CR2: 000000000000001c CR3: 0000000f48a1a004 CR4: 00000000007606e0
[  563.408625] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  563.408627] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  563.904795] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  563.915796] PKRU: 55555554
[  563.915797] Call Trace:
[  563.915807]  cache_set_flush+0xd4/0x6d0 [bcache]
[  563.915812]  process_one_work+0x856/0x1620
[  564.001226] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  564.033563]  ? find_held_lock+0x39/0x1d0
[  564.033567]  ? drain_workqueue+0x380/0x380
[  564.033574]  worker_thread+0x87/0xb80
[  564.062823] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  564.118042]  ? __kthread_parkme+0xb6/0x180
[  564.118046]  ? process_one_work+0x1620/0x1620
[  564.118048]  kthread+0x326/0x3e0
[  564.118050]  ? kthread_create_worker_on_cpu+0xc0/0xc0
[  564.167066] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  564.252441]  ret_from_fork+0x3a/0x50
[  564.252447] Modules linked in: msr rpcrdma sunrpc rdma_ucm ib_iser ib_umad rdma_cm ib_ipoib i40iw configfs iw_cm ib_cm libiscsi scsi_transport_iscsi mlx4_ib ib_uverbs mlx4_en ib_core nls_iso8859_1 nls_cp437 vfat fat intel_rapl skx_edac x86_pkg_temp_thermal coretemp iTCO_wdt iTCO_vendor_support crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel ses raid0 aesni_intel cdc_ether enclosure usbnet ipmi_ssif joydev aes_x86_64 i40e scsi_transport_sas mii bcache md_mod crypto_simd mei_me ioatdma crc64 ptp cryptd pcspkr i2c_i801 mlx4_core glue_helper pps_core mei lpc_ich dca wmi ipmi_si ipmi_devintf nd_pmem dax_pmem nd_btt ipmi_msghandler device_dax pcc_cpufreq button hid_generic usbhid mgag200 i2c_algo_bit drm_kms_helper syscopyarea sysfillrect xhci_pci sysimgblt fb_sys_fops xhci_hcd
  ttm megaraid_sas drm usbcore nfit libnvdimm sg dm_multipath dm_mod scsi_dh_rdac scsi_dh_emc scsi_dh_alua efivarfs
[  564.299390] bcache: bch_count_io_errors() nvme0n1: IO error on writing btree.
[  564.348360] CR2: 000000000000001c
[  564.348362] ---[ end trace b7f0e5cc7b2103b0 ]---

Therefore, it is not enough to only check whether c->gc_thread is NULL,
we should use IS_ERR_OR_NULL() to check both NULL pointer and error
value.

This patch changes the above buggy code piece in this way,
         if (!IS_ERR_OR_NULL(c->gc_thread))
                 kthread_stop(c->gc_thread);

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 0a25774e175a..4cc8a300a557 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1564,7 +1564,7 @@ static void cache_set_flush(struct closure *cl)
 	kobject_put(&c->internal);
 	kobject_del(&c->kobj);
 
-	if (c->gc_thread)
+	if (!IS_ERR_OR_NULL(c->gc_thread))
 		kthread_stop(c->gc_thread);
 
 	if (!IS_ERR_OR_NULL(c->root))
-- 
2.20.1

[PATCH AUTOSEL 5.2 197/249] bcache: avoid a deadlock in bcache_reboot()

[Sasha Levin]

From: Coly Li <colyli@suse.de>

[ Upstream commit a59ff6ccc2bf2e2934b31bbf734f0bc04b5ec78a ]

It is quite frequently to observe deadlock in bcache_reboot() happens
and hang the system reboot process. The reason is, in bcache_reboot()
when calling bch_cache_set_stop() and bcache_device_stop() the mutex
bch_register_lock is held. But in the process to stop cache set and
bcache device, bch_register_lock will be acquired again. If this mutex
is held here, deadlock will happen inside the stopping process. The
aftermath of the deadlock is, whole system reboot gets hung.

The fix is to avoid holding bch_register_lock for the following loops
in bcache_reboot(),
       list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
                bch_cache_set_stop(c);

        list_for_each_entry_safe(dc, tdc, &uncached_devices, list)
                bcache_device_stop(&dc->disk);

A module range variable 'bcache_is_reboot' is added, it sets to true
in bcache_reboot(). In register_bcache(), if bcache_is_reboot is checked
to be true, reject the registration by returning -EBUSY immediately.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/super.c | 40 ++++++++++++++++++++++++++++++++++++++-
 drivers/md/bcache/sysfs.c | 26 +++++++++++++++++++++++++
 2 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 4cc8a300a557..dcd8b319a01e 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -40,6 +40,7 @@ static const char invalid_uuid[] = {
 
 static struct kobject *bcache_kobj;
 struct mutex bch_register_lock;
+bool bcache_is_reboot;
 LIST_HEAD(bch_cache_sets);
 static LIST_HEAD(uncached_devices);
 
@@ -49,6 +50,7 @@ static wait_queue_head_t unregister_wait;
 struct workqueue_struct *bcache_wq;
 struct workqueue_struct *bch_journal_wq;
 
+
 #define BTREE_MAX_PAGES		(256 * 1024 / PAGE_SIZE)
 /* limitation of partitions number on single bcache device */
 #define BCACHE_MINORS		128
@@ -2301,6 +2303,11 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 	if (!try_module_get(THIS_MODULE))
 		return -EBUSY;
 
+	/* For latest state of bcache_is_reboot */
+	smp_mb();
+	if (bcache_is_reboot)
+		return -EBUSY;
+
 	path = kstrndup(buffer, size, GFP_KERNEL);
 	if (!path)
 		goto err;
@@ -2380,6 +2387,9 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 
 static int bcache_reboot(struct notifier_block *n, unsigned long code, void *x)
 {
+	if (bcache_is_reboot)
+		return NOTIFY_DONE;
+
 	if (code == SYS_DOWN ||
 	    code == SYS_HALT ||
 	    code == SYS_POWER_OFF) {
@@ -2392,19 +2402,45 @@ static int bcache_reboot(struct notifier_block *n, unsigned long code, void *x)
 
 		mutex_lock(&bch_register_lock);
 
+		if (bcache_is_reboot)
+			goto out;
+
+		/* New registration is rejected since now */
+		bcache_is_reboot = true;
+		/*
+		 * Make registering caller (if there is) on other CPU
+		 * core know bcache_is_reboot set to true earlier
+		 */
+		smp_mb();
+
 		if (list_empty(&bch_cache_sets) &&
 		    list_empty(&uncached_devices))
 			goto out;
 
+		mutex_unlock(&bch_register_lock);
+
 		pr_info("Stopping all devices:");
 
+		/*
+		 * The reason bch_register_lock is not held to call
+		 * bch_cache_set_stop() and bcache_device_stop() is to
+		 * avoid potential deadlock during reboot, because cache
+		 * set or bcache device stopping process will acqurie
+		 * bch_register_lock too.
+		 *
+		 * We are safe here because bcache_is_reboot sets to
+		 * true already, register_bcache() will reject new
+		 * registration now. bcache_is_reboot also makes sure
+		 * bcache_reboot() won't be re-entered on by other thread,
+		 * so there is no race in following list iteration by
+		 * list_for_each_entry_safe().
+		 */
 		list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
 			bch_cache_set_stop(c);
 
 		list_for_each_entry_safe(dc, tdc, &uncached_devices, list)
 			bcache_device_stop(&dc->disk);
 
-		mutex_unlock(&bch_register_lock);
 
 		/*
 		 * Give an early chance for other kthreads and
@@ -2531,6 +2567,8 @@ static int __init bcache_init(void)
 	bch_debug_init();
 	closure_debug_init();
 
+	bcache_is_reboot = false;
+
 	return 0;
 err:
 	bcache_exit();
diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index bfb437ffb13c..327493f634bb 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -16,6 +16,8 @@
 #include <linux/sort.h>
 #include <linux/sched/clock.h>
 
+extern bool bcache_is_reboot;
+
 /* Default is 0 ("writethrough") */
 static const char * const bch_cache_modes[] = {
 	"writethrough",
@@ -271,6 +273,10 @@ STORE(__cached_dev)
 	struct cache_set *c;
 	struct kobj_uevent_env *env;
 
+	/* no user space access if system is rebooting */
+	if (bcache_is_reboot)
+		return -EBUSY;
+
 #define d_strtoul(var)		sysfs_strtoul(var, dc->var)
 #define d_strtoul_nonzero(var)	sysfs_strtoul_clamp(var, dc->var, 1, INT_MAX)
 #define d_strtoi_h(var)		sysfs_hatoi(var, dc->var)
@@ -408,6 +414,10 @@ STORE(bch_cached_dev)
 	struct cached_dev *dc = container_of(kobj, struct cached_dev,
 					     disk.kobj);
 
+	/* no user space access if system is rebooting */
+	if (bcache_is_reboot)
+		return -EBUSY;
+
 	mutex_lock(&bch_register_lock);
 	size = __cached_dev_store(kobj, attr, buf, size);
 
@@ -511,6 +521,10 @@ STORE(__bch_flash_dev)
 					       kobj);
 	struct uuid_entry *u = &d->c->uuids[d->id];
 
+	/* no user space access if system is rebooting */
+	if (bcache_is_reboot)
+		return -EBUSY;
+
 	sysfs_strtoul(data_csum,	d->data_csum);
 
 	if (attr == &sysfs_size) {
@@ -746,6 +760,10 @@ STORE(__bch_cache_set)
 	struct cache_set *c = container_of(kobj, struct cache_set, kobj);
 	ssize_t v;
 
+	/* no user space access if system is rebooting */
+	if (bcache_is_reboot)
+		return -EBUSY;
+
 	if (attr == &sysfs_unregister)
 		bch_cache_set_unregister(c);
 
@@ -865,6 +883,10 @@ STORE(bch_cache_set_internal)
 {
 	struct cache_set *c = container_of(kobj, struct cache_set, internal);
 
+	/* no user space access if system is rebooting */
+	if (bcache_is_reboot)
+		return -EBUSY;
+
 	return bch_cache_set_store(&c->kobj, attr, buf, size);
 }
 
@@ -1050,6 +1072,10 @@ STORE(__bch_cache)
 	struct cache *ca = container_of(kobj, struct cache, kobj);
 	ssize_t v;
 
+	/* no user space access if system is rebooting */
+	if (bcache_is_reboot)
+		return -EBUSY;
+
 	if (attr == &sysfs_discard) {
 		bool v = strtoul_or_return(buf);
 
-- 
2.20.1

[PATCH AUTOSEL 5.2 198/249] bcache: fix potential deadlock in cached_def_free()

[Sasha Levin]

From: Coly Li <colyli@suse.de>

[ Upstream commit 7e865eba00a3df2dc8c4746173a8ca1c1c7f042e ]

When enable lockdep and reboot system with a writeback mode bcache
device, the following potential deadlock warning is reported by lockdep
engine.

[  101.536569][  T401] kworker/2:2/401 is trying to acquire lock:
[  101.538575][  T401] 00000000bbf6e6c7 ((wq_completion)bcache_writeback_wq){+.+.}, at: flush_workqueue+0x87/0x4c0
[  101.542054][  T401]
[  101.542054][  T401] but task is already holding lock:
[  101.544587][  T401] 00000000f5f305b3 ((work_completion)(&cl->work)#2){+.+.}, at: process_one_work+0x21e/0x640
[  101.548386][  T401]
[  101.548386][  T401] which lock already depends on the new lock.
[  101.548386][  T401]
[  101.551874][  T401]
[  101.551874][  T401] the existing dependency chain (in reverse order) is:
[  101.555000][  T401]
[  101.555000][  T401] -> #1 ((work_completion)(&cl->work)#2){+.+.}:
[  101.557860][  T401]        process_one_work+0x277/0x640
[  101.559661][  T401]        worker_thread+0x39/0x3f0
[  101.561340][  T401]        kthread+0x125/0x140
[  101.562963][  T401]        ret_from_fork+0x3a/0x50
[  101.564718][  T401]
[  101.564718][  T401] -> #0 ((wq_completion)bcache_writeback_wq){+.+.}:
[  101.567701][  T401]        lock_acquire+0xb4/0x1c0
[  101.569651][  T401]        flush_workqueue+0xae/0x4c0
[  101.571494][  T401]        drain_workqueue+0xa9/0x180
[  101.573234][  T401]        destroy_workqueue+0x17/0x250
[  101.575109][  T401]        cached_dev_free+0x44/0x120 [bcache]
[  101.577304][  T401]        process_one_work+0x2a4/0x640
[  101.579357][  T401]        worker_thread+0x39/0x3f0
[  101.581055][  T401]        kthread+0x125/0x140
[  101.582709][  T401]        ret_from_fork+0x3a/0x50
[  101.584592][  T401]
[  101.584592][  T401] other info that might help us debug this:
[  101.584592][  T401]
[  101.588355][  T401]  Possible unsafe locking scenario:
[  101.588355][  T401]
[  101.590974][  T401]        CPU0                    CPU1
[  101.592889][  T401]        ----                    ----
[  101.594743][  T401]   lock((work_completion)(&cl->work)#2);
[  101.596785][  T401]                                lock((wq_completion)bcache_writeback_wq);
[  101.600072][  T401]                                lock((work_completion)(&cl->work)#2);
[  101.602971][  T401]   lock((wq_completion)bcache_writeback_wq);
[  101.605255][  T401]
[  101.605255][  T401]  *** DEADLOCK ***
[  101.605255][  T401]
[  101.608310][  T401] 2 locks held by kworker/2:2/401:
[  101.610208][  T401]  #0: 00000000cf2c7d17 ((wq_completion)events){+.+.}, at: process_one_work+0x21e/0x640
[  101.613709][  T401]  #1: 00000000f5f305b3 ((work_completion)(&cl->work)#2){+.+.}, at: process_one_work+0x21e/0x640
[  101.617480][  T401]
[  101.617480][  T401] stack backtrace:
[  101.619539][  T401] CPU: 2 PID: 401 Comm: kworker/2:2 Tainted: G        W         5.2.0-rc4-lp151.20-default+ #1
[  101.623225][  T401] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/13/2018
[  101.627210][  T401] Workqueue: events cached_dev_free [bcache]
[  101.629239][  T401] Call Trace:
[  101.630360][  T401]  dump_stack+0x85/0xcb
[  101.631777][  T401]  print_circular_bug+0x19a/0x1f0
[  101.633485][  T401]  __lock_acquire+0x16cd/0x1850
[  101.635184][  T401]  ? __lock_acquire+0x6a8/0x1850
[  101.636863][  T401]  ? lock_acquire+0xb4/0x1c0
[  101.638421][  T401]  ? find_held_lock+0x34/0xa0
[  101.640015][  T401]  lock_acquire+0xb4/0x1c0
[  101.641513][  T401]  ? flush_workqueue+0x87/0x4c0
[  101.643248][  T401]  flush_workqueue+0xae/0x4c0
[  101.644832][  T401]  ? flush_workqueue+0x87/0x4c0
[  101.646476][  T401]  ? drain_workqueue+0xa9/0x180
[  101.648303][  T401]  drain_workqueue+0xa9/0x180
[  101.649867][  T401]  destroy_workqueue+0x17/0x250
[  101.651503][  T401]  cached_dev_free+0x44/0x120 [bcache]
[  101.653328][  T401]  process_one_work+0x2a4/0x640
[  101.655029][  T401]  worker_thread+0x39/0x3f0
[  101.656693][  T401]  ? process_one_work+0x640/0x640
[  101.658501][  T401]  kthread+0x125/0x140
[  101.660012][  T401]  ? kthread_create_worker_on_cpu+0x70/0x70
[  101.661985][  T401]  ret_from_fork+0x3a/0x50
[  101.691318][  T401] bcache: bcache_device_free() bcache0 stopped

Here is how the above potential deadlock may happen in reboot/shutdown
code path,
1) bcache_reboot() is called firstly in the reboot/shutdown code path,
   then in bcache_reboot(), bcache_device_stop() is called.
2) bcache_device_stop() sets BCACHE_DEV_CLOSING on d->falgs, then call
   closure_queue(&d->cl) to invoke cached_dev_flush(). And in turn
   cached_dev_flush() calls cached_dev_free() via closure_at()
3) In cached_dev_free(), after stopped writebach kthread
   dc->writeback_thread, the kwork dc->writeback_write_wq is stopping by
   destroy_workqueue().
4) Inside destroy_workqueue(), drain_workqueue() is called. Inside
   drain_workqueue(), flush_workqueue() is called. Then wq->lockdep_map
   is acquired by lock_map_acquire() in flush_workqueue(). After the
   lock acquired the rest part of flush_workqueue() just wait for the
   workqueue to complete.
5) Now we look back at writeback thread routine bch_writeback_thread(),
   in the main while-loop, write_dirty() is called via continue_at() in
   read_dirty_submit(), which is called via continue_at() in while-loop
   level called function read_dirty(). Inside write_dirty() it may be
   re-called on workqueeu dc->writeback_write_wq via continue_at().
   It means when the writeback kthread is stopped in cached_dev_free()
   there might be still one kworker queued on dc->writeback_write_wq
   to execute write_dirty() again.
6) Now this kworker is scheduled on dc->writeback_write_wq to run by
   process_one_work() (which is called by worker_thread()). Before
   calling the kwork routine, wq->lockdep_map is acquired.
7) But wq->lockdep_map is acquired already in step 4), so a A-A lock
   (lockdep terminology) scenario happens.

Indeed on multiple cores syatem, the above deadlock is very rare to
happen, just as the code comments in process_one_work() says,
2263     * AFAICT there is no possible deadlock scenario between the
2264     * flush_work() and complete() primitives (except for
	   single-threaded
2265     * workqueues), so hiding them isn't a problem.

But it is still good to fix such lockdep warning, even no one running
bcache on single core system.

The fix is simple. This patch solves the above potential deadlock by,
- Do not destroy workqueue dc->writeback_write_wq in cached_dev_free().
- Flush and destroy dc->writeback_write_wq in writebach kthread routine
  bch_writeback_thread(), where after quit the thread main while-loop
  and before cached_dev_put() is called.

By this fix, dc->writeback_write_wq will be stopped and destroy before
the writeback kthread stopped, so the chance for a A-A locking on
wq->lockdep_map is disappeared, such A-A deadlock won't happen
any more.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/md/bcache/super.c     | 2 --
 drivers/md/bcache/writeback.c | 4 ++++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index dcd8b319a01e..4ccc5e5fe3a1 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1197,8 +1197,6 @@ static void cached_dev_free(struct closure *cl)
 
 	if (!IS_ERR_OR_NULL(dc->writeback_thread))
 		kthread_stop(dc->writeback_thread);
-	if (dc->writeback_write_wq)
-		destroy_workqueue(dc->writeback_write_wq);
 	if (!IS_ERR_OR_NULL(dc->status_update_thread))
 		kthread_stop(dc->status_update_thread);
 
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 73f0efac2b9f..df0f4e5a051a 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -735,6 +735,10 @@ static int bch_writeback_thread(void *arg)
 		}
 	}
 
+	if (dc->writeback_write_wq) {
+		flush_workqueue(dc->writeback_write_wq);
+		destroy_workqueue(dc->writeback_write_wq);
+	}
 	cached_dev_put(dc);
 	wait_for_kthread_stop();
 
-- 
2.20.1