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Subject[PATCH 4.1 39/65] mm: kmemleak: allow safe memory scanning during kmemleak disabling
Date
4.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Catalin Marinas <catalin.marinas@arm.com>

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.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Vignesh Radhakrishnan <vigneshr@codeaurora.org>
Tested-by: Vignesh Radhakrishnan <vigneshr@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -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);

/*



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