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From:   Yafang Shao <laoar.shao@gmail.com>
To:     bsingharora@gmail.com, akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Yafang Shao <laoar.shao@gmail.com>, Tejun Heo <tj@kernel.org>,
        Josh Snyder <joshs@netflix.com>
Subject: [PATCH] delayacct: clear right task's flag after blkio completes
Date:   Wed, 14 Apr 2021 16:37:20 +0800
Message-Id: <20210414083720.24083-1-laoar.shao@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When I was implementing a latency analyze tool by using task->delays and
other things, I found there's issue in delayacct. The issue is it should
clear the target's flag instead of current's in delayacct_blkio_end().

When I git blame delayacct, I found there're some similar issues we have
fixed in delayacct_blkio_end().
'Commit c96f5471ce7d ("delayacct: Account blkio completion on the correct task")'
fixed the issue that it should account blkio completion on the target
task instead of current.
'Commit b512719f771a ("delayacct: fix crash in delayacct_blkio_end() after delayacct init failure")'
fixed the issue that it should check target task's delays instead of
current task'. It seems that delayacct_blkio_{begin, end} are error prone.
So I introduce a new paratmeter - the target task 'p' into these helpers,
after that change, the callsite will specifilly set the right task, which
should make it less error prone.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Josh Snyder <joshs@netflix.com>
---
 include/linux/delayacct.h | 20 ++++++++++----------
 mm/memory.c               |  8 ++++----
 2 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/linux/delayacct.h b/include/linux/delayacct.h
index 2d3bdcccf5eb..21651f946751 100644
--- a/include/linux/delayacct.h
+++ b/include/linux/delayacct.h
@@ -82,16 +82,16 @@ static inline int delayacct_is_task_waiting_on_io(struct task_struct *p)
 		return 0;
 }
 
-static inline void delayacct_set_flag(int flag)
+static inline void delayacct_set_flag(struct task_struct *p, int flag)
 {
-	if (current->delays)
-		current->delays->flags |= flag;
+	if (p->delays)
+		p->delays->flags |= flag;
 }
 
-static inline void delayacct_clear_flag(int flag)
+static inline void delayacct_clear_flag(struct task_struct *p, int flag)
 {
-	if (current->delays)
-		current->delays->flags &= ~flag;
+	if (p->delays)
+		p->delays->flags &= ~flag;
 }
 
 static inline void delayacct_tsk_init(struct task_struct *tsk)
@@ -114,7 +114,7 @@ static inline void delayacct_tsk_free(struct task_struct *tsk)
 
 static inline void delayacct_blkio_start(void)
 {
-	delayacct_set_flag(DELAYACCT_PF_BLKIO);
+	delayacct_set_flag(current, DELAYACCT_PF_BLKIO);
 	if (current->delays)
 		__delayacct_blkio_start();
 }
@@ -123,7 +123,7 @@ static inline void delayacct_blkio_end(struct task_struct *p)
 {
 	if (p->delays)
 		__delayacct_blkio_end(p);
-	delayacct_clear_flag(DELAYACCT_PF_BLKIO);
+	delayacct_clear_flag(p, DELAYACCT_PF_BLKIO);
 }
 
 static inline int delayacct_add_tsk(struct taskstats *d,
@@ -166,9 +166,9 @@ static inline void delayacct_thrashing_end(void)
 }
 
 #else
-static inline void delayacct_set_flag(int flag)
+static inline void delayacct_set_flag(struct task_struct *p, int flag)
 {}
-static inline void delayacct_clear_flag(int flag)
+static inline void delayacct_clear_flag(struct task_struct *p, int flag)
 {}
 static inline void delayacct_init(void)
 {}
diff --git a/mm/memory.c b/mm/memory.c
index 550405fc3b5e..a013d32a6611 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3296,7 +3296,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	}
 
 
-	delayacct_set_flag(DELAYACCT_PF_SWAPIN);
+	delayacct_set_flag(current, DELAYACCT_PF_SWAPIN);
 	page = lookup_swap_cache(entry, vma, vmf->address);
 	swapcache = page;
 
@@ -3347,7 +3347,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 					vmf->address, &vmf->ptl);
 			if (likely(pte_same(*vmf->pte, vmf->orig_pte)))
 				ret = VM_FAULT_OOM;
-			delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+			delayacct_clear_flag(current, DELAYACCT_PF_SWAPIN);
 			goto unlock;
 		}
 
@@ -3361,13 +3361,13 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		 * owner processes (which may be unknown at hwpoison time)
 		 */
 		ret = VM_FAULT_HWPOISON;
-		delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+		delayacct_clear_flag(current, DELAYACCT_PF_SWAPIN);
 		goto out_release;
 	}
 
 	locked = lock_page_or_retry(page, vma->vm_mm, vmf->flags);
 
-	delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+	delayacct_clear_flag(current, DELAYACCT_PF_SWAPIN);
 	if (!locked) {
 		ret |= VM_FAULT_RETRY;
 		goto out_release;
-- 
2.18.2