Hi Greg,
On 10/07/25 18:39, Greg KH wrote:
On Thu, Jul 10, 2025 at 12:35:43PM +0000, Heyne, Maximilian wrote:
From: Oleg Nesterov <oleg@xxxxxxxxxx>
[ Upstream commit 7904e53ed5a20fc678c01d5d1b07ec486425bb6a ]
do/while_each_thread should be avoided when possible.
Link: https://lkml.kernel.org/r/20230909164501.GA11581@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Stable-dep-of: 7601df8031fd ("fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats")
Cc: stable@xxxxxxxxxxxxxxx
[mheyne: adjusted context]
Signed-off-by: Maximilian Heyne <mheyne@xxxxxxxxx>
---
Compile-tested only.
We're seeing soft lock-ups with 5.10.237 because of the backport of
commit 4fe85bdaabd6 ("fs/proc: do_task_stat: use sig->stats_lock to
gather the threads/children stats").
And this fixes it?
Our testing also showed that after the backport of this commit(on 5.15.y
based release), we don't see the soft lockup anymore.
How?
I think __for_each_thread() is safe whereas while_each_thread() is not safe.
This thread
https://lore.kernel.org/all/20131202152437.GA10896@xxxxxxxxxx/ explains
why while_each_thread() is unsafe.
Thanks,
Harshit
---
fs/proc/array.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 8fba6d39e776..77b94c04e4af 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -512,18 +512,18 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
cgtime = sig->cgtime;
if (whole) {
- struct task_struct *t = task;
+ struct task_struct *t;
min_flt = sig->min_flt;
maj_flt = sig->maj_flt;
gtime = sig->gtime;
rcu_read_lock();
- do {
+ __for_each_thread(sig, t) {
min_flt += t->min_flt;
maj_flt += t->maj_flt;
gtime += task_gtime(t);
- } while_each_thread(task, t);
+ }
Ideally, the code generated here should be identical as before, so why
is this change needed?
> confused,>
greg k-h
