linux-kernel - [PATCH V2] lightnvm: pblk: take write semaphore on metadata

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Date:   Fri,  3 Aug 2018 15:30:11 +0200
From:   "Javier González" <javier@...igon.com>
To:     mb@...htnvm.io
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Javier González <javier@...xlabs.com>
Subject: [PATCH V2] lightnvm: pblk: take write semaphore on metadata

# Changes singe V1:
  - Fix double I/O on the read path (by Matias)
  - Improve commit message (by Jens)

pblk guarantees write ordering at a chunk level through a per open chunk
semaphore. At this point, since we only have an open I/O stream for both
user and GC data, the semaphore is per parallel unit.

Since metadata I/O is synchronous, the semaphore is not needed as
ordering is guaranteed. However, if the metadata scheme changes or
multiple streams are open, this guarantee might not be preserved.

This patch makes sure that all writes go through the semaphore, even for
synchronous I/O. This is consistent with pblk's write I/O model. It also
simplifies maintenance since changes in the metdatada scheme could cause
ordering issues.

Signed-off-by: Javier González <javier@...xlabs.com>
---
 drivers/lightnvm/pblk-core.c | 18 ++++++++++++++++--
 drivers/lightnvm/pblk.h      |  1 +
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
index 00984b486fea..6432faf5b19c 100644
--- a/drivers/lightnvm/pblk-core.c
+++ b/drivers/lightnvm/pblk-core.c
@@ -493,6 +493,20 @@ int pblk_submit_io_sync(struct pblk *pblk, struct nvm_rq *rqd)
 	return nvm_submit_io_sync(dev, rqd);
 }
 
+int pblk_submit_io_sync_sem(struct pblk *pblk, struct nvm_rq *rqd)
+{
+	int ret;
+
+	if (rqd->opcode != NVM_OP_PWRITE)
+		return pblk_submit_io_sync(pblk, rqd);
+
+	pblk_down_page(pblk, rqd->ppa_list, rqd->nr_ppas);
+	ret = pblk_submit_io_sync(pblk, rqd);
+	pblk_up_page(pblk, rqd->ppa_list, rqd->nr_ppas);
+
+	return ret;
+}
+
 static void pblk_bio_map_addr_endio(struct bio *bio)
 {
 	bio_put(bio);
@@ -737,7 +751,7 @@ static int pblk_line_submit_emeta_io(struct pblk *pblk, struct pblk_line *line,
 		}
 	}
 
-	ret = pblk_submit_io_sync(pblk, &rqd);
+	ret = pblk_submit_io_sync_sem(pblk, &rqd);
 	if (ret) {
 		pblk_err(pblk, "emeta I/O submission failed: %d\n", ret);
 		bio_put(bio);
@@ -842,7 +856,7 @@ static int pblk_line_submit_smeta_io(struct pblk *pblk, struct pblk_line *line,
 	 * the write thread is the only one sending write and erase commands,
 	 * there is no need to take the LUN semaphore.
 	 */
-	ret = pblk_submit_io_sync(pblk, &rqd);
+	ret = pblk_submit_io_sync_sem(pblk, &rqd);
 	if (ret) {
 		pblk_err(pblk, "smeta I/O submission failed: %d\n", ret);
 		bio_put(bio);
diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
index 4760af7b6499..6ccc6ad8e1ce 100644
--- a/drivers/lightnvm/pblk.h
+++ b/drivers/lightnvm/pblk.h
@@ -782,6 +782,7 @@ void pblk_log_write_err(struct pblk *pblk, struct nvm_rq *rqd);
 void pblk_log_read_err(struct pblk *pblk, struct nvm_rq *rqd);
 int pblk_submit_io(struct pblk *pblk, struct nvm_rq *rqd);
 int pblk_submit_io_sync(struct pblk *pblk, struct nvm_rq *rqd);
+int pblk_submit_io_sync_sem(struct pblk *pblk, struct nvm_rq *rqd);
 int pblk_submit_meta_io(struct pblk *pblk, struct pblk_line *meta_line);
 struct bio *pblk_bio_map_addr(struct pblk *pblk, void *data,
 			      unsigned int nr_secs, unsigned int len,
-- 
2.7.4