lkml.org 
[lkml]   [2012]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Subject[PATCH v2] mm: correctly synchronize rss-counters at exit/exec
    From
    Date
    mm->rss_stat counters have per-task delta: task->rss_stat, before changing
    task->mm pointer kernel must flush this delta with help of sync_mm_rss().

    do_exit() already calls sync_mm_rss() to flush rss-counters before commiting
    rss-statistics into task->signal->maxrss, taskstats, audit and other stuff.
    Unfortunately kernel do this before calling mm_relese(), 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 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 page-faults.

    Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
    Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    ---
    fs/exec.c | 1 -
    kernel/exit.c | 9 +++++----
    kernel/fork.c | 8 ++++++++
    3 files changed, 13 insertions(+), 5 deletions(-)

    diff --git a/fs/exec.c b/fs/exec.c
    index b1fd202..5be1d97 100644
    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -823,7 +823,6 @@ 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) {
    diff --git a/kernel/exit.c b/kernel/exit.c
    index d8bd3b42..eb12719 100644
    --- a/kernel/exit.c
    +++ b/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 * tsk)
    struct mm_struct *mm = tsk->mm;
    struct core_state *core_state;

    - mm_release(tsk, mm);
    if (!mm)
    return;
    /*
    @@ -959,9 +959,10 @@ 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);
    +
    + /* 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);
    diff --git a/kernel/fork.c b/kernel/fork.c
    index 54662ed..326bb5b 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -751,6 +751,14 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
    }
    tsk->clear_child_tid = NULL;
    }
    +
    + /*
    + * Final rss-counter synchronization. After this point must be
    + * no page-faults into this mm from current context, otherwise
    + * mm->rss_stat will be inconsistent.
    + */
    + if (mm)
    + sync_mm_rss(mm);
    }

    /*


    \
     
     \ /
      Last update: 2012-04-10 19:09    [W:3.999 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site