From e18af8563578c0d292bef9a3f3c0206242f742e5 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Wed, 24 Jun 2015 16:58:26 -0700 Subject: mm: kmemleak: allow safe memory scanning during kmemleak disabling 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 Reported-by: Vignesh Radhakrishnan Tested-by: Vignesh Radhakrishnan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: - Adjust context - Drop changes to kmemleak_free_percpu()] Signed-off-by: Ben Hutchings (cherry picked from commit 3bc68ffc5b43468537a2f0aa415f3b57f3b19d16) Signed-off-by: Willy Tarreau --- mm/kmemleak.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index c3466601d3e7..e9bd6d536d78 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -191,6 +191,8 @@ static struct kmem_cache *scan_area_cache; /* set if tracing memory operations is enabled */ static atomic_t kmemleak_enabled = ATOMIC_INIT(0); +/* 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 atomic_t kmemleak_initialized = ATOMIC_INIT(0); /* enables or disables early logging of the memory operations */ @@ -870,7 +872,7 @@ void __ref kmemleak_free(const void *ptr) { pr_debug("%s(0x%p)\n", __func__, ptr); - if (atomic_read(&kmemleak_enabled) && ptr && !IS_ERR(ptr)) + if (kmemleak_free_enabled && ptr && !IS_ERR(ptr)) delete_object_full((unsigned long)ptr); else if (atomic_read(&kmemleak_early_log)) log_early(KMEMLEAK_FREE, ptr, 0, 0, 0, 0); @@ -1552,6 +1554,13 @@ static void kmemleak_do_cleanup(struct work_struct *work) 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; + rcu_read_lock(); list_for_each_entry_rcu(object, &object_list, object_list) delete_object_full(object->pointer); @@ -1578,6 +1587,8 @@ static void kmemleak_disable(void) /* check whether it is too early for a kernel thread */ if (atomic_read(&kmemleak_initialized)) schedule_work(&cleanup_work); + else + kmemleak_free_enabled = 0; pr_info("Kernel memory leak detector disabled\n"); } @@ -1617,6 +1628,7 @@ void __init kmemleak_init(void) if (!atomic_read(&kmemleak_error)) { atomic_set(&kmemleak_enabled, 1); atomic_set(&kmemleak_early_log, 0); + kmemleak_free_enabled = 1; } local_irq_restore(flags); -- cgit v1.2.3