On 4/19/19 6:04 PM, Coly Li wrote:

In journal_reclaim() ja->cur_idx of each cache will be update to reclaim available journal buckets. Variable 'int n' is used to count how many cache is successfully reclaimed, then n is set to c->journal.key by SET_KEY_PTRS(). Later in journal_write_unlocked(), a for_each_cache() loop will write the jset data onto each cache.

The problem is, if all jouranl buckets on each cache is full, the following code in journal_reclaim(),

529 for_each_cache(ca, c, iter) { 530 struct journal_device *ja = &ca->journal; 531 unsigned int next = (ja->cur_idx + 1) % ca->sb.njournal_buckets; 532 533 /* No space available on this device */ 534 if (next == ja->discard_idx) 535 continue; 536 537 ja->cur_idx = next; 538 k->ptr[n++] = MAKE_PTR(0, 539 bucket_to_sector(c, ca->sb.d[ja->cur_idx]), 540 ca->sb.nr_this_dev); 541 } 542 543 bkey_init(k); 544 SET_KEY_PTRS(k, n);

If there is no available bucket to reclaim, the if() condition at line 534 will always true, and n remains 0. Then at line 544, SET_KEY_PTRS() will set KEY_PTRS field of c->journal.key to 0.

Setting KEY_PTRS field of c->journal.key to 0 is wrong. Because in journal_write_unlocked() the journal data is written in following loop,

649 for (i = 0; i < KEY_PTRS(k); i++) { 650-671 submit journal data to cache device 672 }

If KEY_PTRS field is set to 0 in jouranl_reclaim(), the journal data won't be written to cache device here. If system crahed or rebooted before bkeys of the lost journal entries written into btree nodes, data corruption will be reported during bcache reload after rebooting the system.

Indeed there is only one cache in a cache set, there is no need to set KEY_PTRS field in journal_reclaim() at all. But in order to keep the for_each_cache() logic consistent for now, this patch fixes the above problem by not setting 0 KEY_PTRS of journal key, if there is no bucket available to reclaim.

Cc: stable@vger.kernel.org Signed-off-by: Coly Li colyli@suse.de

---

drivers/md/bcache/journal.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c index 6e18057d1d82..5180bed911ef 100644 --- a/drivers/md/bcache/journal.c +++ b/drivers/md/bcache/journal.c @@ -541,11 +541,11 @@ static void journal_reclaim(struct cache_set *c) ca->sb.nr_this_dev); }

• bkey_init(k);
• SET_KEY_PTRS(k, n);
• if (n)

• if (n) {

• bkey_init(k);
  

• SET_KEY_PTRS(k, n);
  

  c->journal.blocks_free = c->sb.bucket_size >> c->block_bits;
• } out: if (!journal_full(&c->journal)) __closure_wake_up(&c->journal.wait);

@@ -672,6 +672,9 @@ static void journal_write_unlocked(struct closure *cl) ca->journal.seq[ca->journal.cur_idx] = w->data->seq; }

• /* If KEY_PTRS(k) == 0, this jset gets lost in air */
• BUG_ON(i == 0);
• atomic_dec_bug(&fifo_back(&c->journal.pin)); bch_journal_next(&c->journal); journal_reclaim(c);

Reviewed-by: Hannes Reinecke hare@suse.com

Cheers,

Hannes