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Subject[PATCH 4.19 162/219] bcache: fix deadlock in bcache_allocator
Date
From: Andrea Righi <andrea.righi@canonical.com>

[ Upstream commit 84c529aea182939e68f618ed9813740c9165c7eb ]

bcache_allocator can call the following:

bch_allocator_thread()
-> bch_prio_write()
-> bch_bucket_alloc()
-> wait on &ca->set->bucket_wait

But the wake up event on bucket_wait is supposed to come from
bch_allocator_thread() itself => deadlock:

[ 1158.490744] INFO: task bcache_allocato:15861 blocked for more than 10 seconds.
[ 1158.495929] Not tainted 5.3.0-050300rc3-generic #201908042232
[ 1158.500653] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1158.504413] bcache_allocato D 0 15861 2 0x80004000
[ 1158.504419] Call Trace:
[ 1158.504429] __schedule+0x2a8/0x670
[ 1158.504432] schedule+0x2d/0x90
[ 1158.504448] bch_bucket_alloc+0xe5/0x370 [bcache]
[ 1158.504453] ? wait_woken+0x80/0x80
[ 1158.504466] bch_prio_write+0x1dc/0x390 [bcache]
[ 1158.504476] bch_allocator_thread+0x233/0x490 [bcache]
[ 1158.504491] kthread+0x121/0x140
[ 1158.504503] ? invalidate_buckets+0x890/0x890 [bcache]
[ 1158.504506] ? kthread_park+0xb0/0xb0
[ 1158.504510] ret_from_fork+0x35/0x40

Fix by making the call to bch_prio_write() non-blocking, so that
bch_allocator_thread() never waits on itself.

Moreover, make sure to wake up the garbage collector thread when
bch_prio_write() is failing to allocate buckets.

BugLink: https://bugs.launchpad.net/bugs/1784665
BugLink: https://bugs.launchpad.net/bugs/1796292
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
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 | 5 ++++-
drivers/md/bcache/bcache.h | 2 +-
drivers/md/bcache/super.c | 27 +++++++++++++++++++++------
3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
index 9c3beb1e382b..46794cac167e 100644
--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -377,7 +377,10 @@ retry_invalidate:
if (!fifo_full(&ca->free_inc))
goto retry_invalidate;

- bch_prio_write(ca);
+ if (bch_prio_write(ca, false) < 0) {
+ ca->invalidate_needs_gc = 1;
+ wake_up_gc(ca->set);
+ }
}
}
out:
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 83f0b91aeb90..4677b18ac281 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -959,7 +959,7 @@ bool bch_cached_dev_error(struct cached_dev *dc);
__printf(2, 3)
bool bch_cache_set_error(struct cache_set *c, const char *fmt, ...);

-void bch_prio_write(struct cache *ca);
+int bch_prio_write(struct cache *ca, bool wait);
void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent);

extern struct workqueue_struct *bcache_wq;
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 2d60bcdb5b9c..c45d9ad01077 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -525,12 +525,29 @@ static void prio_io(struct cache *ca, uint64_t bucket, int op,
closure_sync(cl);
}

-void bch_prio_write(struct cache *ca)
+int bch_prio_write(struct cache *ca, bool wait)
{
int i;
struct bucket *b;
struct closure cl;

+ pr_debug("free_prio=%zu, free_none=%zu, free_inc=%zu",
+ fifo_used(&ca->free[RESERVE_PRIO]),
+ fifo_used(&ca->free[RESERVE_NONE]),
+ fifo_used(&ca->free_inc));
+
+ /*
+ * Pre-check if there are enough free buckets. In the non-blocking
+ * scenario it's better to fail early rather than starting to allocate
+ * buckets and do a cleanup later in case of failure.
+ */
+ if (!wait) {
+ size_t avail = fifo_used(&ca->free[RESERVE_PRIO]) +
+ fifo_used(&ca->free[RESERVE_NONE]);
+ if (prio_buckets(ca) > avail)
+ return -ENOMEM;
+ }
+
closure_init_stack(&cl);

lockdep_assert_held(&ca->set->bucket_lock);
@@ -540,9 +557,6 @@ void bch_prio_write(struct cache *ca)
atomic_long_add(ca->sb.bucket_size * prio_buckets(ca),
&ca->meta_sectors_written);

- //pr_debug("free %zu, free_inc %zu, unused %zu", fifo_used(&ca->free),
- // fifo_used(&ca->free_inc), fifo_used(&ca->unused));
-
for (i = prio_buckets(ca) - 1; i >= 0; --i) {
long bucket;
struct prio_set *p = ca->disk_buckets;
@@ -560,7 +574,7 @@ void bch_prio_write(struct cache *ca)
p->magic = pset_magic(&ca->sb);
p->csum = bch_crc64(&p->magic, bucket_bytes(ca) - 8);

- bucket = bch_bucket_alloc(ca, RESERVE_PRIO, true);
+ bucket = bch_bucket_alloc(ca, RESERVE_PRIO, wait);
BUG_ON(bucket == -1);

mutex_unlock(&ca->set->bucket_lock);
@@ -589,6 +603,7 @@ void bch_prio_write(struct cache *ca)

ca->prio_last_buckets[i] = ca->prio_buckets[i];
}
+ return 0;
}

static void prio_read(struct cache *ca, uint64_t bucket)
@@ -1884,7 +1899,7 @@ static int run_cache_set(struct cache_set *c)

mutex_lock(&c->bucket_lock);
for_each_cache(ca, c, i)
- bch_prio_write(ca);
+ bch_prio_write(ca, true);
mutex_unlock(&c->bucket_lock);

err = "cannot allocate new UUID bucket";
--
2.20.1


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