From 4983b261bf0438f351270e2d1f2ac38ec010e9ea Mon Sep 17 00:00:00 2001 From: Oxana Kharitonova Date: Fri, 10 Jan 2025 16:03:28 +0000 Subject: [PATCH] hung_task: add task->flags, blocked by coredump to log Resending this patch as I haven't received feedback on my initial submission https://lore.kernel.org/all/20241204182953.10854-1-oxana@cloudflare.com/ For the processes which are terminated abnormally the kernel can provide a coredump if enabled. When the coredump is performed, the process and all its threads are put into the D state (TASK_UNINTERRUPTIBLE | TASK_FREEZABLE). On the other hand, we have kernel thread khungtaskd which monitors the processes in the D state. If the task stuck in the D state more than kernel.hung_task_timeout_secs, the hung_task alert appears in the kernel log. The higher memory usage of a process, the longer it takes to create coredump, the longer tasks are in the D state. We have hung_task alerts for the processes with memory usage above 10Gb. Although, our kernel.hung_task_timeout_secs is 10 sec when the default is 120 sec. Adding additional information to the log that the task is blocked by coredump will help with monitoring. Another approach might be to completely filter out alerts for such tasks, but in that case we would lose transparency about what is putting pressure on some system resources, e.g. we saw an increase in I/O when coredump occurs due its writing to disk. Additionally, it would be helpful to have task_struct->flags in the log from the function sched_show_task(). Currently it prints task_struct->thread_info->flags, this seems misleading as the line starts with "task:xxxx". Link: https://lkml.kernel.org/r/20250110160328.64947-1-oxana@cloudflare.com Signed-off-by: Oxana Kharitonova Cc: Al Viro Cc: Ben Segall Cc: Christian Brauner Cc: Dietmar Eggemann Cc: Ingo Molnar Cc: Jan Kara Cc: Juri Lelli Cc: Mel Gorman Cc: Peter Zijlstra (Intel) Cc: Steven Rostedt Cc: Valentin Schneider Cc: Vincent Guittot Signed-off-by: Andrew Morton --- kernel/hung_task.c | 2 ++ kernel/sched/core.c | 4 ++-- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/hung_task.c b/kernel/hung_task.c index c18717189f32..953169893a95 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -147,6 +147,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) print_tainted(), init_utsname()->release, (int)strcspn(init_utsname()->version, " "), init_utsname()->version); + if (t->flags & PF_POSTCOREDUMP) + pr_err(" Blocked by coredump.\n"); pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\"" " disables this message.\n"); sched_show_task(t); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3e5a6bf587f9..77b6af12e146 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7701,9 +7701,9 @@ void sched_show_task(struct task_struct *p) if (pid_alive(p)) ppid = task_pid_nr(rcu_dereference(p->real_parent)); rcu_read_unlock(); - pr_cont(" stack:%-5lu pid:%-5d tgid:%-5d ppid:%-6d flags:0x%08lx\n", + pr_cont(" stack:%-5lu pid:%-5d tgid:%-5d ppid:%-6d task_flags:0x%08lx flags:0x%08lx\n", free, task_pid_nr(p), task_tgid_nr(p), - ppid, read_task_thread_flags(p)); + ppid, p->flags, read_task_thread_flags(p)); print_worker_info(KERN_INFO, p); print_stop_info(KERN_INFO, p);