On Mon, Jun 02, 2014 at 03:42:07PM -0700, Andrew Morton wrote:
> On Fri, 30 May 2014 02:51:10 -0400 Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> wrote:
>
> > Currently memory error handler handles action optional errors in the deferred
> > manner by default. And if a recovery aware application wants to handle it
> > immediately, it can do it by setting PF_MCE_EARLY flag. However, such signal
> > can be sent only to the main thread, so it's problematic if the application
> > wants to have a dedicated thread to handler such signals.
> >
> > So this patch adds dedicated thread support to memory error handler. We have
> > PF_MCE_EARLY flags for each thread separately, so with this patch AO signal
> > is sent to the thread with PF_MCE_EARLY flag set, not the main thread. If
> > you want to implement a dedicated thread, you call prctl() to set PF_MCE_EARLY
> > on the thread.
> >
> > Memory error handler collects processes to be killed, so this patch lets it
> > check PF_MCE_EARLY flag on each thread in the collecting routines.
> >
> > No behavioral change for all non-early kill cases.
> >
> > ...
> >
> > --- mmotm-2014-05-21-16-57.orig/mm/memory-failure.c
> > +++ mmotm-2014-05-21-16-57/mm/memory-failure.c
> > @@ -380,15 +380,44 @@ static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,
> > }
> > }
> >
> > -static int task_early_kill(struct task_struct *tsk, int force_early)
> > +/*
> > + * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
> > + * on behalf of the thread group. Return task_struct of the (first found)
> > + * dedicated thread if found, and return NULL otherwise.
> > + */
> > +static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
> > +{
> > + struct task_struct *t;
> > + rcu_read_lock();
> > + for_each_thread(tsk, t)
> > + if ((t->flags & PF_MCE_PROCESS) && (t->flags & PF_MCE_EARLY))
> > + goto found;
> > + t = NULL;
> > +found:
> > + rcu_read_unlock();
> > + return t;
> > +}
> > +
> > +/*
> > + * Determine whether a given process is "early kill" process which expects
> > + * to be signaled when some page under the process is hwpoisoned.
> > + * Return task_struct of the dedicated thread (main thread unless explicitly
> > + * specified) if the process is "early kill," and otherwise returns NULL.
> > + */
> > +static struct task_struct *task_early_kill(struct task_struct *tsk,
> > + int force_early)
> > {
> > + struct task_struct *t;
> > if (!tsk->mm)
> > - return 0;
> > + return NULL;
> > if (force_early)
> > - return 1;
> > - if (tsk->flags & PF_MCE_PROCESS)
> > - return !!(tsk->flags & PF_MCE_EARLY);
> > - return sysctl_memory_failure_early_kill;
> > + return tsk;
> > + t = find_early_kill_thread(tsk);
> > + if (t)
> > + return t;
> > + if (sysctl_memory_failure_early_kill)
> > + return tsk;
> > + return NULL;
> > }
>
> The above two functions are to be called under
> read_lock(tasklist_lock), which is rather important...
>
> Given this requirement, did find_early_kill_thread() need rcu_read_lock()?
Right, we don't need this rcu_read_lock(). The following hunk should fix it.
Thanks,
Naoya Horiguchi
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index b0f48e34dec5..6fdc9a2eeb2f 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -297,18 +297,17 @@ struct to_kill {
* Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO)
* on behalf of the thread group. Return task_struct of the (first found)
* dedicated thread if found, and return NULL otherwise.
+ *
+ * We already hold read_lock(&tasklist_lock) in the caller, so we don't
+ * have to call rcu_read_lock/unlock() in this function.
*/
static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
{
struct task_struct *t;
- rcu_read_lock();
for_each_thread(tsk, t)
if ((t->flags & PF_MCE_PROCESS) && (t->flags & PF_MCE_EARLY))
- goto found;
- t = NULL;
-found:
- rcu_read_unlock();
- return t;
+ return t;
+ return NULL;
}
/*
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