FAILED: patch "[PATCH] taskstats: retain dead thread stats in TGID queries" failed to apply to 5.10-stable tree

FAILED: patch "[PATCH] taskstats: retain dead thread stats in TGID queries" failed to apply to 5.10-stable tree

[gregkh]

The patch below does not apply to the 5.10-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 <stable@vger.kernel.org>.

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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x b3e4fbb04220efc3bc022bcf31b5689d39c6b111
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026072047-tameness-overlap-0f45@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From b3e4fbb04220efc3bc022bcf31b5689d39c6b111 Mon Sep 17 00:00:00 2001
From: Yiyang Chen <cyyzero16@gmail.com>
Date: Mon, 13 Apr 2026 23:45:44 +0800
Subject: [PATCH] taskstats: retain dead thread stats in TGID queries

Patch series "taskstats: fix TGID dead-thread stat retention", v3.

This series fixes a taskstats TGID aggregation bug where fields added in
the TGID query path were not preserved after thread exit, and adds a
kselftest covering the regression.

The first patch keeps the cached TGID aggregate used for dead threads in
step with the fields already accumulated for live threads, and also fixes
the final TGID exit notification emitted when group_dead is true.

The second patch adds a kselftest that verifies TGID CPU stats do not
regress after a worker thread exits and has been reaped.


This patch (of 2):

fill_stats_for_tgid() builds TGID stats from two sources: the cached
aggregate in signal->stats and a scan of the live threads in the group.

However, fill_tgid_exit() only accumulates delay accounting into
signal->stats.  This means that once a thread exits, TGID queries lose the
fields that fill_stats_for_tgid() adds for live threads.

This gap was introduced incrementally by two earlier changes that extended
fill_stats_for_tgid() but did not make the corresponding update to
fill_tgid_exit():

- commit 8c733420bdd5 ("taskstats: add e/u/stime for TGID command")
  added ac_etime, ac_utime, and ac_stime to the TGID query path.
- commit b663a79c1915 ("taskstats: add context-switch counters")
  added nvcsw and nivcsw to the TGID query path.

As a result, those fields were accounted for live threads in TGID queries,
but were dropped from the cached TGID aggregate after thread exit.  The
final TGID exit notification emitted when group_dead is true also copies
that cached aggregate, so it loses the same fields.

Factor the per-task TGID accumulation into tgid_stats_add_task() and use
it in both fill_stats_for_tgid() and fill_tgid_exit().  This keeps the
cached aggregate used for dead threads aligned with the live-thread
accumulation used by TGID queries.

Link: https://lore.kernel.org/cover.1776094300.git.cyyzero16@gmail.com
Link: https://lore.kernel.org/abd2a15d33343636ab5ba43d540bcfe508bd66c7.1776094300.git.cyyzero16@gmail.com
Fixes: 8c733420bdd5 ("taskstats: add e/u/stime for TGID command")
Fixes: b663a79c1915 ("taskstats: add context-switch counters")
Signed-off-by: Yiyang Chen <cyyzero16@gmail.com>
Acked-by: Balbir Singh <balbirs@nvidia.com>
Cc: Dr. Thomas Orgis <thomas.orgis@uni-hamburg.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Wang Yaxin <wang.yaxin@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 73bd6a6a7893..2cd0172d0516 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -210,13 +210,39 @@ static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
 	return 0;
 }
 
+static void tgid_stats_add_task(struct taskstats *stats,
+				struct task_struct *tsk, u64 now_ns)
+{
+	u64 delta, utime, stime;
+
+	/*
+	 * Each accounting subsystem calls its functions here to
+	 * accumulate its per-task stats for tsk, into the per-tgid structure
+	 *
+	 *	per-task-foo(stats, tsk);
+	 */
+	delayacct_add_tsk(stats, tsk);
+
+	/* calculate task elapsed time in nsec */
+	delta = now_ns - tsk->start_time;
+	/* Convert to micro seconds */
+	do_div(delta, NSEC_PER_USEC);
+	stats->ac_etime += delta;
+
+	task_cputime(tsk, &utime, &stime);
+	stats->ac_utime += div_u64(utime, NSEC_PER_USEC);
+	stats->ac_stime += div_u64(stime, NSEC_PER_USEC);
+
+	stats->nvcsw += tsk->nvcsw;
+	stats->nivcsw += tsk->nivcsw;
+}
+
 static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 {
 	struct task_struct *tsk, *first;
 	unsigned long flags;
 	int rc = -ESRCH;
-	u64 delta, utime, stime;
-	u64 start_time;
+	u64 now_ns;
 
 	/*
 	 * Add additional stats from live tasks except zombie thread group
@@ -233,30 +259,12 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 	else
 		memset(stats, 0, sizeof(*stats));
 
-	start_time = ktime_get_ns();
+	now_ns = ktime_get_ns();
 	for_each_thread(first, tsk) {
 		if (tsk->exit_state)
 			continue;
-		/*
-		 * Accounting subsystem can call its functions here to
-		 * fill in relevant parts of struct taskstsats as follows
-		 *
-		 *	per-task-foo(stats, tsk);
-		 */
-		delayacct_add_tsk(stats, tsk);
 
-		/* calculate task elapsed time in nsec */
-		delta = start_time - tsk->start_time;
-		/* Convert to micro seconds */
-		do_div(delta, NSEC_PER_USEC);
-		stats->ac_etime += delta;
-
-		task_cputime(tsk, &utime, &stime);
-		stats->ac_utime += div_u64(utime, NSEC_PER_USEC);
-		stats->ac_stime += div_u64(stime, NSEC_PER_USEC);
-
-		stats->nvcsw += tsk->nvcsw;
-		stats->nivcsw += tsk->nivcsw;
+		tgid_stats_add_task(stats, tsk, now_ns);
 	}
 
 	unlock_task_sighand(first, &flags);
@@ -275,18 +283,14 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 static void fill_tgid_exit(struct task_struct *tsk)
 {
 	unsigned long flags;
+	u64 now_ns;
 
 	spin_lock_irqsave(&tsk->sighand->siglock, flags);
 	if (!tsk->signal->stats)
 		goto ret;
 
-	/*
-	 * Each accounting subsystem calls its functions here to
-	 * accumalate its per-task stats for tsk, into the per-tgid structure
-	 *
-	 *	per-task-foo(tsk->signal->stats, tsk);
-	 */
-	delayacct_add_tsk(tsk->signal->stats, tsk);
+	now_ns = ktime_get_ns();
+	tgid_stats_add_task(tsk->signal->stats, tsk, now_ns);
 ret:
 	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
 	return;

[PATCH 5.10.y 1/2] taskstats: fill_stats_for_tgid: use for_each_thread()

[Sasha Levin]

From: Oleg Nesterov <oleg@redhat.com>

[ Upstream commit ed5378a387fd7c382497f2abcf4605e030b64044 ]

do/while_each_thread should be avoided when possible.

Plus I _think_ this change allows to avoid lock_task_sighand() but I am
not sure, I forgot everything about taskstats.  In any case, this code
does not look right in that the same thread can be accounted twice:
taskstats_exit() can account the exiting thread in signal->stats and drop
->siglock but this thread is still on the thread-group list, so
lock_task_sighand() can't help.

Link: https://lkml.kernel.org/r/20230909214951.GA24274@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: b3e4fbb04220 ("taskstats: retain dead thread stats in TGID queries")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/taskstats.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 14c65293a865c2..a0b04f2b223496 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -211,9 +211,8 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 	else
 		memset(stats, 0, sizeof(*stats));
 
-	tsk = first;
 	start_time = ktime_get_ns();
-	do {
+	for_each_thread(first, tsk) {
 		if (tsk->exit_state)
 			continue;
 		/*
@@ -236,7 +235,7 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 
 		stats->nvcsw += tsk->nvcsw;
 		stats->nivcsw += tsk->nivcsw;
-	} while_each_thread(first, tsk);
+	}
 
 	unlock_task_sighand(first, &flags);
 	rc = 0;
-- 
2.53.0

[PATCH 5.10.y 2/2] taskstats: retain dead thread stats in TGID queries

[Sasha Levin]

From: Yiyang Chen <cyyzero16@gmail.com>

[ Upstream commit b3e4fbb04220efc3bc022bcf31b5689d39c6b111 ]

Patch series "taskstats: fix TGID dead-thread stat retention", v3.

This series fixes a taskstats TGID aggregation bug where fields added in
the TGID query path were not preserved after thread exit, and adds a
kselftest covering the regression.

The first patch keeps the cached TGID aggregate used for dead threads in
step with the fields already accumulated for live threads, and also fixes
the final TGID exit notification emitted when group_dead is true.

The second patch adds a kselftest that verifies TGID CPU stats do not
regress after a worker thread exits and has been reaped.

This patch (of 2):

fill_stats_for_tgid() builds TGID stats from two sources: the cached
aggregate in signal->stats and a scan of the live threads in the group.

However, fill_tgid_exit() only accumulates delay accounting into
signal->stats.  This means that once a thread exits, TGID queries lose the
fields that fill_stats_for_tgid() adds for live threads.

This gap was introduced incrementally by two earlier changes that extended
fill_stats_for_tgid() but did not make the corresponding update to
fill_tgid_exit():

- commit 8c733420bdd5 ("taskstats: add e/u/stime for TGID command")
  added ac_etime, ac_utime, and ac_stime to the TGID query path.
- commit b663a79c1915 ("taskstats: add context-switch counters")
  added nvcsw and nivcsw to the TGID query path.

As a result, those fields were accounted for live threads in TGID queries,
but were dropped from the cached TGID aggregate after thread exit.  The
final TGID exit notification emitted when group_dead is true also copies
that cached aggregate, so it loses the same fields.

Factor the per-task TGID accumulation into tgid_stats_add_task() and use
it in both fill_stats_for_tgid() and fill_tgid_exit().  This keeps the
cached aggregate used for dead threads aligned with the live-thread
accumulation used by TGID queries.

Link: https://lore.kernel.org/cover.1776094300.git.cyyzero16@gmail.com
Link: https://lore.kernel.org/abd2a15d33343636ab5ba43d540bcfe508bd66c7.1776094300.git.cyyzero16@gmail.com
Fixes: 8c733420bdd5 ("taskstats: add e/u/stime for TGID command")
Fixes: b663a79c1915 ("taskstats: add context-switch counters")
Signed-off-by: Yiyang Chen <cyyzero16@gmail.com>
Acked-by: Balbir Singh <balbirs@nvidia.com>
Cc: Dr. Thomas Orgis <thomas.orgis@uni-hamburg.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Wang Yaxin <wang.yaxin@zte.com.cn>
Cc: Yang Yang <yang.yang29@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/taskstats.c | 62 ++++++++++++++++++++++++----------------------
 1 file changed, 33 insertions(+), 29 deletions(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index a0b04f2b223496..a2d24fb7cf407f 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -188,13 +188,39 @@ static int fill_stats_for_pid(pid_t pid, struct taskstats *stats)
 	return 0;
 }
 
+static void tgid_stats_add_task(struct taskstats *stats,
+				struct task_struct *tsk, u64 now_ns)
+{
+	u64 delta, utime, stime;
+
+	/*
+	 * Each accounting subsystem calls its functions here to
+	 * accumulate its per-task stats for tsk, into the per-tgid structure
+	 *
+	 *	per-task-foo(stats, tsk);
+	 */
+	delayacct_add_tsk(stats, tsk);
+
+	/* calculate task elapsed time in nsec */
+	delta = now_ns - tsk->start_time;
+	/* Convert to micro seconds */
+	do_div(delta, NSEC_PER_USEC);
+	stats->ac_etime += delta;
+
+	task_cputime(tsk, &utime, &stime);
+	stats->ac_utime += div_u64(utime, NSEC_PER_USEC);
+	stats->ac_stime += div_u64(stime, NSEC_PER_USEC);
+
+	stats->nvcsw += tsk->nvcsw;
+	stats->nivcsw += tsk->nivcsw;
+}
+
 static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 {
 	struct task_struct *tsk, *first;
 	unsigned long flags;
 	int rc = -ESRCH;
-	u64 delta, utime, stime;
-	u64 start_time;
+	u64 now_ns;
 
 	/*
 	 * Add additional stats from live tasks except zombie thread group
@@ -211,30 +237,12 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 	else
 		memset(stats, 0, sizeof(*stats));
 
-	start_time = ktime_get_ns();
+	now_ns = ktime_get_ns();
 	for_each_thread(first, tsk) {
 		if (tsk->exit_state)
 			continue;
-		/*
-		 * Accounting subsystem can call its functions here to
-		 * fill in relevant parts of struct taskstsats as follows
-		 *
-		 *	per-task-foo(stats, tsk);
-		 */
-		delayacct_add_tsk(stats, tsk);
-
-		/* calculate task elapsed time in nsec */
-		delta = start_time - tsk->start_time;
-		/* Convert to micro seconds */
-		do_div(delta, NSEC_PER_USEC);
-		stats->ac_etime += delta;
 
-		task_cputime(tsk, &utime, &stime);
-		stats->ac_utime += div_u64(utime, NSEC_PER_USEC);
-		stats->ac_stime += div_u64(stime, NSEC_PER_USEC);
-
-		stats->nvcsw += tsk->nvcsw;
-		stats->nivcsw += tsk->nivcsw;
+		tgid_stats_add_task(stats, tsk, now_ns);
 	}
 
 	unlock_task_sighand(first, &flags);
@@ -253,18 +261,14 @@ static int fill_stats_for_tgid(pid_t tgid, struct taskstats *stats)
 static void fill_tgid_exit(struct task_struct *tsk)
 {
 	unsigned long flags;
+	u64 now_ns;
 
 	spin_lock_irqsave(&tsk->sighand->siglock, flags);
 	if (!tsk->signal->stats)
 		goto ret;
 
-	/*
-	 * Each accounting subsystem calls its functions here to
-	 * accumalate its per-task stats for tsk, into the per-tgid structure
-	 *
-	 *	per-task-foo(tsk->signal->stats, tsk);
-	 */
-	delayacct_add_tsk(tsk->signal->stats, tsk);
+	now_ns = ktime_get_ns();
+	tgid_stats_add_task(tsk->signal->stats, tsk, now_ns);
 ret:
 	spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
 	return;
-- 
2.53.0