Re: [Crash-utility] [PATCH] Fix "ps/vm" commands to display the memory usage for exiting tasks
On 2023/08/23 14:44, Lianbo Jiang wrote:
When a task is exiting, usually kernel marks its flags as
'PF_EXITING',
but even so, sometimes the mm_struct has not been freed, it might still
be valid. For such tasks, the "ps/vm" commands won't display the memory
usage. For example:
crash> ps 47070
PID PPID CPU TASK ST %MEM VSZ RSS COMM
47070 1 0 ffff9ba7c4910000 UN 0.0 0 0 ra_ris.parse
crash> vm 47070
PID: 47070 TASK: ffff9ba7c4910000 CPU: 0 COMMAND: "ra_ris.parse"
MM PGD RSS TOTAL_VM
0 0 0k 0k
To be honest, this is a corner case, but it has already occurred in
actual production environments. Given that, let's allow the "ps/vm"
commands to try to display the memory usage for this case, but it does
not guarantee that it can work well at any time, which still depends on
how far the mm_struct deconstruction has proceeded.
Agree to display it, and looks like the deconstruction is done after
task->mm is set to NULL, so it looks fine to me.
void __noreturn do_exit(long code)
{
...
exit_signals(tsk); /* sets PF_EXITING */
...
exit_mm();
static void exit_mm(void)
{
struct mm_struct *mm = current->mm;
...
current->mm = NULL; ## task->mm is set to NULL here
...
mmput(mm); ## release the resources actually
On the other hand, the mm->mm_count is decremented in mmput(), is there
need to check it?
void mmput(struct mm_struct *mm)
{
might_sleep();
if (atomic_dec_and_test(&mm->mm_users))
__mmput(mm);
}
static inline void __mmput(struct mm_struct *mm)
{
...
exit_mmap(mm);
...
mmdrop(mm);
}
static inline void mmdrop(struct mm_struct *mm)
{
...
if (unlikely(atomic_dec_and_test(&mm->mm_count)))
__mmdrop(mm);
}
Thanks,
Kazu
>
> With the patch:
> crash> ps 47070
> PID PPID CPU TASK ST %MEM VSZ RSS COMM
> 47070 1 0 ffff9ba7c4910000 UN 90.8 38461228 31426444
ra_ris.parse
> crash> vm 47070
> PID: 47070 TASK: ffff9ba7c4910000 CPU: 0 COMMAND:
"ra_ris.parse"
> MM PGD RSS TOTAL_VM
> ffff9bad6e873840 ffff9baee0544000 31426444k 38461228k
> VMA START END FLAGS FILE
> ffff9bafdbe1d6c8 400000 8c5000 8000875
/data1/rishome/ra_cu_cn_412/sbin/ra_ris.parse
> ...
>
> Reported-by: Buland Kumar Singh <bsingh(a)redhat.com>
> Signed-off-by: Lianbo Jiang <lijiang(a)redhat.com>
> ---
> memory.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/memory.c b/memory.c
> index 5d76c5d7fe6f..7d59c0555a0e 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -4792,10 +4792,12 @@ get_task_mem_usage(ulong task, struct task_mem_usage *tm)
> {
> struct task_context *tc;
> long rss = 0, rss_cache = 0;
> + int mm_count = 0;
> + ulong addr;
>
> BZERO(tm, sizeof(struct task_mem_usage));
>
> - if (IS_ZOMBIE(task) || IS_EXITING(task))
> + if (IS_ZOMBIE(task))
> return;
>
> tc = task_to_context(task);
> @@ -4805,7 +4807,14 @@ get_task_mem_usage(ulong task, struct task_mem_usage *tm)
>
> tm->mm_struct_addr = tc->mm_struct;
>
> - if (!task_mm(task, TRUE))
> + if (!(addr = task_mm(task, TRUE)))
> + return;
> +
> + if (!readmem(addr + OFFSET(mm_struct_mm_count), KVADDR, &mm_count,
> + sizeof(int), "mm_struct mm_count", RETURN_ON_ERROR))
> + return;
> +
> + if (IS_EXITING(task) && mm_count <= 0)
> return;
>
> if (VALID_MEMBER(mm_struct_rss))