mm/memory-failure.c: don't let collect_procs() skip over processes for MF_ACTION_REQUIRED

When Linux sees an "action optional" machine check (where h/w has reported
an error that is not in the current execution path) we generally do not
want to signal a process, since most processes do not have a SIGBUS
handler - we'd just prematurely terminate the process for a problem that
they might never actually see.

task_early_kill() decides whether to consider a process - and it checks
whether this specific process has been marked for early signals with
"prctl", or if the system administrator has requested early signals for
all processes using /proc/sys/vm/memory_failure_early_kill.

But for MF_ACTION_REQUIRED case we must not defer.  The error is in the
execution path of the current thread so we must send the SIGBUS
immediatley.

Fix by passing a flag argument through collect_procs*() to
task_early_kill() so it knows whether we can defer or must take action.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Chen Gong <gong.chen@linux.jf.intel.com>
Cc: <stable@vger.kernel.org>	[3.2+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 9 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 89ad452182bb..ed339c505d55 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -380,10 +380,12 @@ static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,
         }
 }
 
-static int task_early_kill(struct task_struct *tsk)
+static int task_early_kill(struct task_struct *tsk, int force_early)
 {
         if (!tsk->mm)
                 return 0;
+        if (force_early)
+                return 1;
         if (tsk->flags & PF_MCE_PROCESS)
                 return !!(tsk->flags & PF_MCE_EARLY);
         return sysctl_memory_failure_early_kill;
@@ -393,7 +395,7 @@ static int task_early_kill(struct task_struct *tsk)
  * Collect processes when the error hit an anonymous page.
  */
 static void collect_procs_anon(struct page *page, struct list_head *to_kill,
-                              struct to_kill **tkc)
+                              struct to_kill **tkc, int force_early)
 {
         struct vm_area_struct *vma;
         struct task_struct *tsk;
@@ -409,7 +411,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
         for_each_process (tsk) {
                 struct anon_vma_chain *vmac;
 
-                if (!task_early_kill(tsk))
+                if (!task_early_kill(tsk, force_early))
                         continue;
                 anon_vma_interval_tree_foreach(vmac, &av->rb_root,
                                                pgoff, pgoff) {
@@ -428,7 +430,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill,
  * Collect processes when the error hit a file mapped page.
  */
 static void collect_procs_file(struct page *page, struct list_head *to_kill,
-                              struct to_kill **tkc)
+                              struct to_kill **tkc, int force_early)
 {
         struct vm_area_struct *vma;
         struct task_struct *tsk;
@@ -439,7 +441,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
         for_each_process(tsk) {
                 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
 
-                if (!task_early_kill(tsk))
+                if (!task_early_kill(tsk, force_early))
                         continue;
 
                 vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
@@ -465,7 +467,8 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill,
  * First preallocate one tokill structure outside the spin locks,
  * so that we can kill at least one process reasonably reliable.
  */
-static void collect_procs(struct page *page, struct list_head *tokill)
+static void collect_procs(struct page *page, struct list_head *tokill,
+                                int force_early)
 {
         struct to_kill *tk;
 
@@ -476,9 +479,9 @@ static void collect_procs(struct page *page, struct list_head *tokill)
         if (!tk)
                 return;
         if (PageAnon(page))
-                collect_procs_anon(page, tokill, &tk);
+                collect_procs_anon(page, tokill, &tk, force_early);
         else
-                collect_procs_file(page, tokill, &tk);
+                collect_procs_file(page, tokill, &tk, force_early);
         kfree(tk);
 }
 
@@ -963,7 +966,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
          * there's nothing that can be done.
          */
         if (kill)
-                collect_procs(ppage, &tokill);
+                collect_procs(ppage, &tokill, flags & MF_ACTION_REQUIRED);
 
         ret = try_to_unmap(ppage, ttu);
         if (ret != SWAP_SUCCESS)