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authorTejun Heo <tj@kernel.org>2018-11-08 12:15:15 -0800
committerTejun Heo <tj@kernel.org>2018-11-20 08:12:20 -0800
commite9d81a1bc2c48ea9782e3e8b53875f419766ef47 (patch)
tree67c9ed401a07cd336c8ec53708019238024b89f8 /kernel
parentf2ce1065e767fc7da106a5f5381d1e8f842dc6f4 (diff)
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cgroup: fix CSS_TASK_ITER_PROCS
CSS_TASK_ITER_PROCS implements process-only iteration by making css_task_iter_advance() skip tasks which aren't threadgroup leaders; however, when an iteration is started css_task_iter_start() calls the inner helper function css_task_iter_advance_css_set() instead of css_task_iter_advance(). As the helper doesn't have the skip logic, when the first task to visit is a non-leader thread, it doesn't get skipped correctly as shown in the following example. # ps -L 2030 PID LWP TTY STAT TIME COMMAND 2030 2030 pts/0 Sl+ 0:00 ./test-thread 2030 2031 pts/0 Sl+ 0:00 ./test-thread # mkdir -p /sys/fs/cgroup/x/a/b # echo threaded > /sys/fs/cgroup/x/a/cgroup.type # echo threaded > /sys/fs/cgroup/x/a/b/cgroup.type # echo 2030 > /sys/fs/cgroup/x/a/cgroup.procs # cat /sys/fs/cgroup/x/a/cgroup.threads 2030 2031 # cat /sys/fs/cgroup/x/cgroup.procs 2030 # echo 2030 > /sys/fs/cgroup/x/a/b/cgroup.threads # cat /sys/fs/cgroup/x/cgroup.procs 2031 2030 The last read of cgroup.procs is incorrectly showing non-leader 2031 in cgroup.procs output. This can be fixed by updating css_task_iter_advance() to handle the first advance and css_task_iters_tart() to call css_task_iter_advance() instead of the inner helper. After the fix, the same commands result in the following (correct) result: # ps -L 2062 PID LWP TTY STAT TIME COMMAND 2062 2062 pts/0 Sl+ 0:00 ./test-thread 2062 2063 pts/0 Sl+ 0:00 ./test-thread # mkdir -p /sys/fs/cgroup/x/a/b # echo threaded > /sys/fs/cgroup/x/a/cgroup.type # echo threaded > /sys/fs/cgroup/x/a/b/cgroup.type # echo 2062 > /sys/fs/cgroup/x/a/cgroup.procs # cat /sys/fs/cgroup/x/a/cgroup.threads 2062 2063 # cat /sys/fs/cgroup/x/cgroup.procs 2062 # echo 2062 > /sys/fs/cgroup/x/a/b/cgroup.threads # cat /sys/fs/cgroup/x/cgroup.procs 2062 Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> Fixes: 8cfd8147df67 ("cgroup: implement cgroup v2 thread support") Cc: stable@vger.kernel.org # v4.14+
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup/cgroup.c29
1 files changed, 17 insertions, 12 deletions
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 6aaf5dd5383b..1f84977fab47 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4202,20 +4202,25 @@ static void css_task_iter_advance(struct css_task_iter *it)
lockdep_assert_held(&css_set_lock);
repeat:
- /*
- * Advance iterator to find next entry. cset->tasks is consumed
- * first and then ->mg_tasks. After ->mg_tasks, we move onto the
- * next cset.
- */
- next = it->task_pos->next;
+ if (it->task_pos) {
+ /*
+ * Advance iterator to find next entry. cset->tasks is
+ * consumed first and then ->mg_tasks. After ->mg_tasks,
+ * we move onto the next cset.
+ */
+ next = it->task_pos->next;
- if (next == it->tasks_head)
- next = it->mg_tasks_head->next;
+ if (next == it->tasks_head)
+ next = it->mg_tasks_head->next;
- if (next == it->mg_tasks_head)
+ if (next == it->mg_tasks_head)
+ css_task_iter_advance_css_set(it);
+ else
+ it->task_pos = next;
+ } else {
+ /* called from start, proceed to the first cset */
css_task_iter_advance_css_set(it);
- else
- it->task_pos = next;
+ }
/* if PROCS, skip over tasks which aren't group leaders */
if ((it->flags & CSS_TASK_ITER_PROCS) && it->task_pos &&
@@ -4255,7 +4260,7 @@ void css_task_iter_start(struct cgroup_subsys_state *css, unsigned int flags,
it->cset_head = it->cset_pos;
- css_task_iter_advance_css_set(it);
+ css_task_iter_advance(it);
spin_unlock_irq(&css_set_lock);
}