In the kernel, long waits can trigger hung task warnings. However, some
warnings are undesirable and unnecessary - for example, a hung task
warning triggered when a background kworker waits for writeback
completion during resource cleanup(like the context of
mem_cgroup_css_free()). This kworker does not affect any user behavior
and there is no erroneous behavior at the kernel code level, yet it
triggers an annoying hung task warning.
This patch adds a new flag to task_struct to instruct the hung task
detector to ignore such cases, as suggested by Andrew Morton in [1].
Also introduces current_set/clear_flags() to prepare for the next patch.
[1]: https://lore.kernel.org/cgroups/20250917152155.5a8ddb3e4ff813289ea0b4c9@linux-foundation.org/
Signed-off-by: Julian Sun <sunjunchao@bytedance.com>
---
include/linux/sched.h | 12 +++++++++++-
kernel/hung_task.c | 6 ++++++
2 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f8188b833350..cd70ff051b2a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1718,6 +1718,16 @@ static inline char task_state_to_char(struct task_struct *tsk)
return task_index_to_char(task_state_index(tsk));
}
+static inline void current_set_flags(unsigned int flags)
+{
+ current->flags |= flags;
+}
+
+static inline void current_clear_flags(unsigned int flags)
+{
+ current->flags &= ~flags;
+}
+
extern struct pid *cad_pid;
/*
@@ -1747,7 +1757,7 @@ extern struct pid *cad_pid;
* I am cleaning dirty pages from some other bdi. */
#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
#define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */
-#define PF__HOLE__00800000 0x00800000
+#define PF_DONT_HUNG 0x00800000 /* Don't trigger hung task warning when waiting for something */
#define PF__HOLE__01000000 0x01000000
#define PF__HOLE__02000000 0x02000000
#define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 8708a1205f82..b16d72276d01 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -208,6 +208,12 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
t->last_switch_time = jiffies;
return;
}
+
+ if (t->flags & PF_DONT_HUNG) {
+ t->last_switch_time = jiffies;
+ return;
+ }
+
if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
return;
--
2.39.5