Patch "mm: kmemleak: allow safe memory scanning during kmemleak disabling" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

mm: kmemleak: allow safe memory scanning during kmemleak disabling

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-kmemleak-allow-safe-memory-scanning-during-kmemleak-disabling.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Catalin Marinas <[email protected]>
Date: Wed, 24 Jun 2015 16:58:26 -0700
Subject: mm: kmemleak: allow safe memory scanning during kmemleak disabling

From: Catalin Marinas <[email protected]>

commit c5f3b1a51a591c18c8b33983908e7fdda6ae417e upstream.

The kmemleak scanning thread can run for minutes. Callbacks like kmemleak_free() are allowed during this time, the race being taken care of by the object->lock spinlock. Such lock also prevents a memory block from being freed or unmapped while it is being scanned by blocking the kmemleak_free() -> ... -> __delete_object() function until the lock is released in scan_object().

When a kmemleak error occurs (e.g. it fails to allocate its metadata), kmemleak_enabled is set and __delete_object() is no longer called on freed objects. If kmemleak_scan is running at the same time, kmemleak_free() no longer waits for the object scanning to complete, allowing the corresponding memory block to be freed or unmapped (in the case of vfree()). This leads to kmemleak_scan potentially triggering a page fault.

This patch separates the kmemleak_free() enabling/disabling from the overall kmemleak_enabled nob so that we can defer the disabling of the object freeing tracking until the scanning thread completed. The kmemleak_free_part() is deliberately ignored by this patch since this is only called during boot before the scanning thread started.

---
 mm/kmemleak.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

@@ -195,6 +195,8 @@ static struct kmem_cache *scan_area_cach
 
 /* set if tracing memory operations is enabled */
 static int kmemleak_enabled;
+/* same as above but only for the kmemleak_free() callback */
+static int kmemleak_free_enabled;
 /* set in the late_initcall if there were no errors */
 static int kmemleak_initialized;
 /* enables or disables early logging of the memory operations */

@@ -942,7 +944,7 @@ void __ref kmemleak_free(const void *ptr
 {
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
+	if (kmemleak_free_enabled && ptr && !IS_ERR(ptr))
 		delete_object_full((unsigned long)ptr);
 	else if (kmemleak_early_log)
 		log_early(KMEMLEAK_FREE, ptr, 0, 0);

@@ -982,7 +984,7 @@ void __ref kmemleak_free_percpu(const vo
 
 	pr_debug("%s(0x%p)\n", __func__, ptr);
 
-	if (kmemleak_enabled && ptr && !IS_ERR(ptr))
+	if (kmemleak_free_enabled && ptr && !IS_ERR(ptr))
 		for_each_possible_cpu(cpu)
 			delete_object_full((unsigned long)per_cpu_ptr(ptr,
 								      cpu));

@@ -1750,6 +1752,13 @@ static void kmemleak_do_cleanup(struct w
 	mutex_lock(&scan_mutex);
 	stop_scan_thread();
 
+	/*
+	 * Once the scan thread has stopped, it is safe to no longer track
+	 * object freeing. Ordering of the scan thread stopping and the memory
+	 * accesses below is guaranteed by the kthread_stop() function.
+	 */
+	kmemleak_free_enabled = 0;
+
 	if (!kmemleak_found_leaks)
 		__kmemleak_do_cleanup();
 	else

@@ -1776,6 +1785,8 @@ static void kmemleak_disable(void)
 	/* check whether it is too early for a kernel thread */
 	if (kmemleak_initialized)
 		schedule_work(&cleanup_work);
+	else
+		kmemleak_free_enabled = 0;
 
 	pr_info("Kernel memory leak detector disabled\n");
 }

@@ -1840,8 +1851,10 @@ void __init kmemleak_init(void)
 	if (kmemleak_error) {
 		local_irq_restore(flags);
 		return;
-	} else
+	} else {
 		kmemleak_enabled = 1;
+		kmemleak_free_enabled = 1;
+	}
 	local_irq_restore(flags);
 
 	/*

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/arm64-do-not-attempt-to-use-init_mm-in-reset_context.patch queue-4.0/mm-kmemleak-allow-safe-memory-scanning-during-kmemleak-disabling.patch queue-4.0/arm64-entry-fix-context-tracking-for-el0_sp_pc.patch queue-4.0/arm64-vdso-work-around-broken-elf-toolchains-in-makefile.patch queue-4.0/mm-kmemleak_alloc_percpu-should-follow-the-gfp-from-per_alloc.patch queue-4.0/arm64-mm-fix-freeing-of-the-wrong-memmap-entries-with-sparsemem_vmemmap.patch