lightnvm: pblk: simplify path on REQ_PREFLUSH

On REQ_PREFLUSH, directly tag the I/O context flags to signal a flush in
the write to cache path, instead of finding the correct entry context
and imposing a memory barrier. This simplifies the code and might
potentially prevent race conditions when adding functionality to the
write path.
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-cache.c

@@ -43,8 +43,10 @@ int pblk_write_to_cache(struct pblk *pblk, struct bio *bio, unsigned long flags)
 	if (unlikely(!bio_has_data(bio)))
 		goto out;
 
-	w_ctx.flags = flags;
 	pblk_ppa_set_empty(&w_ctx.ppa);
+	w_ctx.flags = flags;
+	if (bio->bi_opf & REQ_PREFLUSH)
+		w_ctx.flags |= PBLK_FLUSH_ENTRY;
 
 	for (i = 0; i < nr_entries; i++) {
 		void *data = bio_data(bio);

drivers/lightnvm/pblk-rb.c

@@ -355,7 +355,6 @@ static int pblk_rb_sync_point_set(struct pblk_rb *rb, struct bio *bio,
 {
 	struct pblk_rb_entry *entry;
 	unsigned int subm, sync_point;
-	int flags;
 
 	subm = READ_ONCE(rb->subm);
 
@@ -369,12 +368,6 @@ static int pblk_rb_sync_point_set(struct pblk_rb *rb, struct bio *bio,
 	sync_point = (pos == 0) ? (rb->nr_entries - 1) : (pos - 1);
 	entry = &rb->entries[sync_point];
 
-	flags = READ_ONCE(entry->w_ctx.flags);
-	flags |= PBLK_FLUSH_ENTRY;
-
-	/* Release flags on context. Protect from writes */
-	smp_store_release(&entry->w_ctx.flags, flags);
-
 	/* Protect syncs */
 	smp_store_release(&rb->sync_point, sync_point);
 
@@ -454,6 +447,7 @@ static int pblk_rb_may_write_flush(struct pblk_rb *rb, unsigned int nr_entries,
 
 	/* Protect from read count */
 	smp_store_release(&rb->mem, mem);
+
 	return 1;
 }