On Fri, 20 Apr 2012 22:41:29 +0200
Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >> IOW, what do you think about the trivial patch below? Uncompiled,
> >> untested, probably incomplete. acct_update_integrals() looks
> >> suspicious too.
> >
> > what a mess! =)
>
> Thanks ;)
>
> But it is much, much simpler than your patches, don't you agree?
<taps his foot>
Here's what we currently have:
From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
Subject: mm: correctly synchronize rss-counters at exit/exec
mm->rss_stat counters have per-task delta: task->rss_stat. Before
changing task->mm pointer the kernel must flush this delta with
sync_mm_rss().
do_exit() already calls sync_mm_rss() to flush the rss-counters before
committing the rss statistics into task->signal->maxrss, taskstats, audit
and other stuff. Unfortunately the kernel does this before calling
mm_release(), which can call put_user() for processing
task->clear_child_tid. So at this point we can trigger page-faults and
task->rss_stat becomes non-zero again. As a result mm->rss_stat becomes
inconsistent and check_mm() will print something like this:
| BUG: Bad rss-counter state mm:ffff88020813c380 idx:1 val:-1
| BUG: Bad rss-counter state mm:ffff88020813c380 idx:2 val:1
This patch moves sync_mm_rss() into mm_release(), and moves mm_release()
out of do_exit() and calls it earlier. After mm_release() there should be
no pagefaults.
[akpm@xxxxxxxxxxxxxxxxxxxx: tweak comment]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
Reported-by: Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 1 -
kernel/exit.c | 13 ++++++++-----
kernel/fork.c | 8 ++++++++
3 files changed, 16 insertions(+), 6 deletions(-)
diff -puN fs/exec.c~mm-correctly-synchronize-rss-counters-at-exit-exec fs/exec.c
--- a/fs/exec.c~mm-correctly-synchronize-rss-counters-at-exit-exec
+++ a/fs/exec.c
@@ -823,7 +823,6 @@ static int exec_mmap(struct mm_struct *m
/* 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) {
diff -puN kernel/exit.c~mm-correctly-synchronize-rss-counters-at-exit-exec kernel/exit.c
--- a/kernel/exit.c~mm-correctly-synchronize-rss-counters-at-exit-exec
+++ a/kernel/exit.c
@@ -423,6 +423,7 @@ void daemonize(const char *name, ...)
* user space pages. We don't need them, and if we didn't close them
* they would be locked into memory.
*/
+ mm_release(current, current->mm);
exit_mm(current);
/*
* We don't want to get frozen, in case system-wide hibernation
@@ -640,7 +641,6 @@ static void exit_mm(struct task_struct *
struct mm_struct *mm = tsk->mm;
struct core_state *core_state;
- mm_release(tsk, mm);
if (!mm)
return;
/*
@@ -959,9 +959,13 @@ 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);
+
+ /* Set exit_code before complete_vfork_done() in mm_release() */
+ tsk->exit_code = code;
+
+ /* Release mm and sync mm's RSS info before statistics gathering */
+ mm_release(tsk, tsk->mm);
+
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
hrtimer_cancel(&tsk->signal->real_timer);
@@ -974,7 +978,6 @@ void do_exit(long code)
tty_audit_exit();
audit_free(tsk);
- tsk->exit_code = code;
taskstats_exit(tsk, group_dead);
exit_mm(tsk);
diff -puN kernel/fork.c~mm-correctly-synchronize-rss-counters-at-exit-exec kernel/fork.c
--- a/kernel/fork.c~mm-correctly-synchronize-rss-counters-at-exit-exec
+++ a/kernel/fork.c
@@ -782,6 +782,14 @@ void mm_release(struct task_struct *tsk,
}
tsk->clear_child_tid = NULL;
}
+
+ /*
+ * Final rss-counter synchronization. After this point there must be
+ * no pagefaults into this mm from the current context. Otherwise
+ * mm->rss_stat will be inconsistent.
+ */
+ if (mm)
+ sync_mm_rss(mm);
}
/*
_
--
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