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Subject[PATCH 4.19 184/271] bcache: Revert "bcache: fix high CPU occupancy during journal"
Date
From: Coly Li <colyli@suse.de>

commit 249a5f6da57c28a903c75d81505d58ec8c10030d upstream.

This reverts commit c4dc2497d50d9c6fb16aa0d07b6a14f3b2adb1e0.

This patch enlarges a race between normal btree flush code path and
flush_btree_write(), which causes deadlock when journal space is
exhausted. Reverts this patch makes the race window from 128 btree
nodes to only 1 btree nodes.

Fixes: c4dc2497d50d ("bcache: fix high CPU occupancy during journal")
Signed-off-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Cc: Tang Junhui <tang.junhui.linux@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/bcache/bcache.h | 2 -
drivers/md/bcache/journal.c | 47 ++++++++++++++------------------------------
drivers/md/bcache/util.h | 2 -
3 files changed, 15 insertions(+), 36 deletions(-)

--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -708,8 +708,6 @@ struct cache_set {

#define BUCKET_HASH_BITS 12
struct hlist_head bucket_hash[1 << BUCKET_HASH_BITS];
-
- DECLARE_HEAP(struct btree *, flush_btree);
};

struct bbio {
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -390,12 +390,6 @@ err:
}

/* Journalling */
-#define journal_max_cmp(l, r) \
- (fifo_idx(&c->journal.pin, btree_current_write(l)->journal) < \
- fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))
-#define journal_min_cmp(l, r) \
- (fifo_idx(&c->journal.pin, btree_current_write(l)->journal) > \
- fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))

static void btree_flush_write(struct cache_set *c)
{
@@ -403,35 +397,25 @@ static void btree_flush_write(struct cac
* Try to find the btree node with that references the oldest journal
* entry, best is our current candidate and is locked if non NULL:
*/
- struct btree *b;
- int i;
+ struct btree *b, *best;
+ unsigned int i;

atomic_long_inc(&c->flush_write);
-
retry:
- spin_lock(&c->journal.lock);
- if (heap_empty(&c->flush_btree)) {
- for_each_cached_btree(b, c, i)
- if (btree_current_write(b)->journal) {
- if (!heap_full(&c->flush_btree))
- heap_add(&c->flush_btree, b,
- journal_max_cmp);
- else if (journal_max_cmp(b,
- heap_peek(&c->flush_btree))) {
- c->flush_btree.data[0] = b;
- heap_sift(&c->flush_btree, 0,
- journal_max_cmp);
- }
- }
-
- for (i = c->flush_btree.used / 2 - 1; i >= 0; --i)
- heap_sift(&c->flush_btree, i, journal_min_cmp);
- }
+ best = NULL;

- b = NULL;
- heap_pop(&c->flush_btree, b, journal_min_cmp);
- spin_unlock(&c->journal.lock);
+ for_each_cached_btree(b, c, i)
+ if (btree_current_write(b)->journal) {
+ if (!best)
+ best = b;
+ else if (journal_pin_cmp(c,
+ btree_current_write(best)->journal,
+ btree_current_write(b)->journal)) {
+ best = b;
+ }
+ }

+ b = best;
if (b) {
mutex_lock(&b->write_lock);
if (!btree_current_write(b)->journal) {
@@ -873,8 +857,7 @@ int bch_journal_alloc(struct cache_set *
j->w[0].c = c;
j->w[1].c = c;

- if (!(init_heap(&c->flush_btree, 128, GFP_KERNEL)) ||
- !(init_fifo(&j->pin, JOURNAL_PIN, GFP_KERNEL)) ||
+ if (!(init_fifo(&j->pin, JOURNAL_PIN, GFP_KERNEL)) ||
!(j->w[0].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS)) ||
!(j->w[1].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS)))
return -ENOMEM;
--- a/drivers/md/bcache/util.h
+++ b/drivers/md/bcache/util.h
@@ -113,8 +113,6 @@ do { \

#define heap_full(h) ((h)->used == (h)->size)

-#define heap_empty(h) ((h)->used == 0)
-
#define DECLARE_FIFO(type, name) \
struct { \
size_t front, back, size, mask; \

\
 
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