FAILED: patch "[PATCH] blk-wbt: Fix detection of dirty-throttled tasks" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x f814bdda774c183b0cc15ec8f3b6e7c6f4527ba5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024021921-unspoiled-despite-59cc@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

f814bdda774c ("blk-wbt: Fix detection of dirty-throttled tasks") ba91c849fa50 ("blk-rq-qos: store a gendisk instead of request_queue in struct rq_qos") 3963d84df797 ("blk-rq-qos: constify rq_qos_ops")
ce57b558604e ("blk-rq-qos: make rq_qos_add and rq_qos_del more useful") b494f9c566ba ("blk-rq-qos: move rq_qos_add and rq_qos_del out of line") de185b56e8a6 ("blk-cgroup: pass a gendisk to blkcg_schedule_throttle") 9df3e65139b9 ("blk-iocost: simplify ioc_name")
14a6e2eb7df5 ("block: don't allow the same type rq_qos add more than once") 5cf9c91ba927 ("block: serialize all debugfs operations using q->debugfs_mutex") 8a177a36da6c ("blk-iolatency: Fix inflight count imbalances and IO hangs on offline") c97ab271576d ("blk-cgroup: remove unneeded includes from <linux/blk-cgroup.h>") 7f20ba7c42fd ("blk-cgroup: remove pointless CONFIG_BLOCK ifdefs") bbb1ebe7a909 ("blk-cgroup: replace bio_blkcg with bio_blkcg_css") dec223c92a46 ("blk-cgroup: move struct blkcg to block/blk-cgroup.h") 397c9f46ee4d ("blk-cgroup: move blkcg_{pin,unpin}_online out of line") 216889aad362 ("blk-cgroup: move blk_cgroup_congested out line") d589ae0d4460 ("Merge tag 'for-5.18/block-2022-04-01' of git://git.kernel.dk/linux-block")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f814bdda774c183b0cc15ec8f3b6e7c6f4527ba5 Mon Sep 17 00:00:00 2001
From: Jan Kara <[email protected]>
Date: Tue, 23 Jan 2024 18:58:26 +0100
Subject: [PATCH] blk-wbt: Fix detection of dirty-throttled tasks

The detection of dirty-throttled tasks in blk-wbt has been subtly broken since its beginning in 2016. Namely if we are doing cgroup writeback and the throttled task is not in the root cgroup, balance_dirty_pages() will set dirty_sleep for the non-root bdi_writeback structure. However blk-wbt checks dirty_sleep only in the root cgroup bdi_writeback structure. Thus detection of recently throttled tasks is not working in this case (we noticed this when we switched to cgroup v2 and suddently writeback was slow).

Since blk-wbt has no easy way to get to proper bdi_writeback and furthermore its intention has always been to work on the whole device rather than on individual cgroups, just move the dirty_sleep timestamp from bdi_writeback to backing_dev_info. That fixes the checking for recently throttled task and saves memory for everybody as a bonus.

index 5ba3cd574eac..0c0e270a8265 100644
@@ -163,9 +163,9 @@ static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
  */
 static bool wb_recent_wait(struct rq_wb *rwb)
 {
-	struct bdi_writeback *wb = &rwb->rqos.disk->bdi->wb;
+	struct backing_dev_info *bdi = rwb->rqos.disk->bdi;
 
-	return time_before(jiffies, wb->dirty_sleep + HZ);
+	return time_before(jiffies, bdi->last_bdp_sleep + HZ);
 }
 
 static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,

index ae12696ec492..2ad261082bba 100644
@@ -141,8 +141,6 @@ struct bdi_writeback {
 	struct delayed_work dwork;	/* work item used for writeback */
 	struct delayed_work bw_dwork;	/* work item used for bandwidth estimate */
 
-	unsigned long dirty_sleep;	/* last wait */
-
 	struct list_head bdi_node;	/* anchored at bdi->wb_list */
 
 #ifdef CONFIG_CGROUP_WRITEBACK

@@ -179,6 +177,11 @@ struct backing_dev_info {
 	 * any dirty wbs, which is depended upon by bdi_has_dirty().
 	 */
 	atomic_long_t tot_write_bandwidth;
+	/*
+	 * Jiffies when last process was dirty throttled on this bdi. Used by
+	 * blk-wbt.
+	 */
+	unsigned long last_bdp_sleep;
 
 	struct bdi_writeback wb;  /* the root writeback info for this bdi */
 	struct list_head wb_list; /* list of all wbs */

index 1e3447bccdb1..e039d05304dd 100644
@@ -436,7 +436,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 	INIT_LIST_HEAD(&wb->work_list);
 	INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
 	INIT_DELAYED_WORK(&wb->bw_dwork, wb_update_bandwidth_workfn);
-	wb->dirty_sleep = jiffies;
 
 	err = fprop_local_init_percpu(&wb->completions, gfp);
 	if (err)

@@ -921,6 +920,7 @@ int bdi_init(struct backing_dev_info *bdi)
 	INIT_LIST_HEAD(&bdi->bdi_list);
 	INIT_LIST_HEAD(&bdi->wb_list);
 	init_waitqueue_head(&bdi->wb_waitq);
+	bdi->last_bdp_sleep = jiffies;
 
 	return cgwb_bdi_init(bdi);
 }

index cd4e4ae77c40..cc37fa7f3364 100644
@@ -1921,7 +1921,7 @@ static int balance_dirty_pages(struct bdi_writeback *wb,
 			break;
 		}
 		__set_current_state(TASK_KILLABLE);
-		wb->dirty_sleep = now;
+		bdi->last_bdp_sleep = jiffies;
 		io_schedule_timeout(pause);
 
 		current->dirty_paused_when = now + pause;