On 06/07, Linus Torvalds wrote:
>
> It does totally insane things in xacct_add_tsk(). You can't call
> "sync_mm_rss(mm)" on somebody elses mm,
Damn, I am stupid. Yes, I forgot about fill_stats_for_pid().
And I didn't bother to look at get_task_mm() which clearly
shows that this tsk can be !current.
We can add the "p == current" check as Hugh suggested.
But,
> Doing it
> *anywhere* where mm is not clearly "current->mm" is wrong.
Agreed.
How about v2? It adds sync_mm_rss() into taskstats_exit(). Note
that it preserves the "tsk->mm != NULL" check we currently have.
I think it should be removed (see the changelog), but even if I
am right I'd prefer to do this in a separate patch.
------------------------------------------------------------------------------
Subject: [PATCH] correctly synchronize rss-counters at exit/exec
A simplified version of Konstantin Khlebnikov's patch.
do_exit() and exec_mmap() call sync_mm_rss() before mm_release()
does put_user(clear_child_tid) which can update task->rss_stat
and thus make mm->rss_stat inconsistent. This triggers the "BUG:"
printk in check_mm().
- Move the final sync_mm_rss() from do_exit() to exit_mm(), and
change exec_mmap() to call sync_mm_rss() after mm_release() to
make check_mm() happy.
Perhaps we should simply move it into mm_release() and call it
unconditionally to catch the "task->rss_stat != 0 && !task->mm"
bugs.
- Since taskstats_exit() is called before exit_mm(), add another
sync_mm_rss() into taskstats_exit() for xacct_add_tsk() who
actually uses rss_stat. As Linus pointed out, it is not sane
to move it into xacct_add_tsk().
Probably we should also shift acct_update_integrals(), and
"tsk->mm != NULL" check looks equally unneeded.
Reported-by: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
Tested-by: Martin Mokrejs <mmokrejs@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
---
fs/exec.c | 2 +-
kernel/exit.c | 5 ++---
kernel/taskstats.c | 2 ++
3 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index a79786a..da27b91 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -819,10 +819,10 @@ static int exec_mmap(struct mm_struct *mm)
/* Notify parent that we're no longer interested in the old VM */
tsk = current;
old_mm = current->mm;
- sync_mm_rss(old_mm);
mm_release(tsk, old_mm);
if (old_mm) {
+ sync_mm_rss(old_mm);
/*
* Make sure that if there is a core dump in progress
* for the old mm, we get out and die instead of going
diff --git a/kernel/exit.c b/kernel/exit.c
index 0e40041..38c4a91 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -655,6 +655,8 @@ static void exit_mm(struct task_struct * tsk)
mm_release(tsk, mm);
if (!mm)
return;
+
+ sync_mm_rss(mm);
/*
* Serialize with any possible pending coredump.
* We must hold mmap_sem around checking core_state
@@ -966,9 +968,6 @@ void do_exit(long code)
preempt_count());
acct_update_integrals(tsk);
- /* sync mm's RSS info before statistics gathering */
- if (tsk->mm)
- sync_mm_rss(tsk->mm);
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
hrtimer_cancel(&tsk->signal->real_timer);
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index e660464..55d1103 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -630,6 +630,8 @@ void taskstats_exit(struct task_struct *tsk, int group_dead)
if (!stats)
goto err;
+ if (tsk->mm)
+ sync_mm_rss(tsk->mm);
fill_stats(tsk, stats);
/*
--
1.5.5.1
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