linux-kernel - [PATCH 2/2] memory-failure: Don't let collect_procs() skip over processes for MF_ACTION

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Message-Id: <d6101e631fb61e9e097207939a93faa799be9a82.1400607328.git.tony.luck@intel.com>
Date:	Tue, 20 May 2014 09:46:43 -0700
From:	Tony Luck <tony.luck@...el.com>
To:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:	Andi Kleen <andi@...stfloor.org>, Borislav Petkov <bp@...e.de>,
	Chen Gong <gong.chen@...ux.jf.intel.com>
Subject: [PATCH 2/2] memory-failure: 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@...el.com>
---
 mm/memory-failure.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 642c8434b166..f0967f72991c 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)
-- 
1.8.4.1

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