mm/memory-failure: prioritize prctl(PR_MCE_KILL) over vm.memory_failure_early_kill

Patch series "hwpoison: fixes signaling on memory error"

This is a small patchset to solve issues in memory error handler to send
SIGBUS to proper process/thread as expected in configuration.  Please
see descriptions in individual patches for more details.

This patch (of 2):

Early-kill policy is controlled from two types of settings, one is
per-process setting prctl(PR_MCE_KILL) and the other is system-wide
setting vm.memory_failure_early_kill.  Users expect per-process setting
to override system-wide setting as many other settings do, but
early-kill setting doesn't work as such.

For example, if a system configures vm.memory_failure_early_kill to 1
(enabled), a process receives SIGBUS even if it's configured to
explicitly disable PF_MCE_KILL by prctl().  That's not desirable for
applications with their own policies.

This patch is suggesting to change the priority of these two types of
settings, by checking sysctl_memory_failure_early_kill only when a given
process has the default kill policy.

Note that this patch is solving a thread choice issue too.

Originally, collect_procs() always chooses the main thread when
vm.memory_failure_early_kill is 1, even if the process has a dedicated
thread for memory error handling.  SIGBUS should be sent to the
dedicated thread if early-kill is enabled via
vm.memory_failure_early_kill as we are doing for PR_MCE_KILL_EARLY
processes.

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Link: http://lkml.kernel.org/r/1591321039-22141-1-git-send-email-naoya.horiguchi@nec.com
Link: http://lkml.kernel.org/r/1591321039-22141-2-git-send-email-naoya.horiguchi@nec.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index ababa368cb68084537d2176c0966f3d6598f5f9c..848de82cd54772a9335e2de8e7a9cc18078bd461 100644 (file)
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -402,9 +402,15 @@ static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
 {
        struct task_struct *t;
 
-       for_each_thread(tsk, t)
-               if ((t->flags & PF_MCE_PROCESS) && (t->flags & PF_MCE_EARLY))
-                       return t;
+       for_each_thread(tsk, t) {
+               if (t->flags & PF_MCE_PROCESS) {
+                       if (t->flags & PF_MCE_EARLY)
+                               return t;
+               } else {
+                       if (sysctl_memory_failure_early_kill)
+                               return t;
+               }
+       }
        return NULL;
 }
 
@@ -417,17 +423,11 @@ static struct task_struct *find_early_kill_thread(struct task_struct *tsk)
 static struct task_struct *task_early_kill(struct task_struct *tsk,
                                           int force_early)
 {
-       struct task_struct *t;
        if (!tsk->mm)
                return NULL;
        if (force_early)
                return tsk;
-       t = find_early_kill_thread(tsk);
-       if (t)
-               return t;
-       if (sysctl_memory_failure_early_kill)
-               return tsk;
-       return NULL;
+       return find_early_kill_thread(tsk);
 }
 
 /*