Hi,
在 2023/08/10 21:43, Yu Kuai 写道:
在 2023/08/10 11:51, Li Lingfeng 写道:
From: Li Lingfeng <lilingfeng3@xxxxxxxxxx>
Commit a13696b83da4 ("blk-iolatency: Make initialization lazy") adds
a mutex named "init_mutex" in blk_iolatency_try_init for the race
condition of initializing RQ_QOS_LATENCY.
Now a new lock has been add to struct request_queue by commit
a13bd91be223
("block/rq_qos: protect rq_qos apis with a new lock"). And it has been
held in blkg_conf_open_bdev before calling blk_iolatency_init.
So it's not necessary to keep init_mutex in blk_iolatency_try_init, just
remove it.
Since init_mutex has been removed, blk_iolatency_try_init can be
open-coded back to iolatency_set_limit() like ioc_qos_write().
Reviewed-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Thanks,
Kuai
Signed-off-by: Li Lingfeng <lilingfeng3@xxxxxxxxxx>
---
v1->v2: open-code blk_iolatency_try_init()
v2->v3: add lockdep check
block/blk-iolatency.c | 35 +++++++++++------------------------
1 file changed, 11 insertions(+), 24 deletions(-)
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index fd5fec989e39..c16aef4be036 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -824,29 +824,6 @@ static void iolatency_clear_scaling(struct
blkcg_gq *blkg)
}
}
-static int blk_iolatency_try_init(struct blkg_conf_ctx *ctx)
-{
- static DEFINE_MUTEX(init_mutex);
- int ret;
-
- ret = blkg_conf_open_bdev(ctx);
- if (ret)
- return ret;
-
- /*
- * blk_iolatency_init() may fail after rq_qos_add() succeeds
which can
- * confuse iolat_rq_qos() test. Make the test and init atomic.
- */
- mutex_lock(&init_mutex);
-
- if (!iolat_rq_qos(ctx->bdev->bd_queue))
- ret = blk_iolatency_init(ctx->bdev->bd_disk);
-
- mutex_unlock(&init_mutex);
-
- return ret;
-}
-
static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char
*buf,
size_t nbytes, loff_t off)
{
@@ -861,7 +838,17 @@ static ssize_t iolatency_set_limit(struct
kernfs_open_file *of, char *buf,
blkg_conf_init(&ctx, buf);
- ret = blk_iolatency_try_init(&ctx);
+ ret = blkg_conf_open_bdev(&ctx);
+ if (ret)
+ goto out;
+
+ /*
+ * blk_iolatency_init() may fail after rq_qos_add() succeeds
which can
+ * confuse iolat_rq_qos() test. Make the test and init atomic.
+ */
The original mutex and above comments is used to avoid the problem that
blk_iolatency_init() is not atomic:
t1: t2:
if (!iolat_rq_qos)
// not exist
blk_iolatency_init
rq_qos_add
blkcg_activate_policy
// failed
if (!iolat_rq_qos)
// now exist
rq_qos_del
...
// continue while rq_qos is deleted
Now that this problem doesn't exist, I think it's ok just to remove this
comment.
Thanks,
Kuai
+ lockdep_assert_held(ctx.bdev->bd_queue->rq_qos_mutex);
+ if (!iolat_rq_qos(ctx.bdev->bd_queue))
+ ret = blk_iolatency_init(ctx.bdev->bd_disk);
if (ret)
goto out;
.
