From a587a2355e9458cf9c422b79e888f8c137235f5d Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Fri, 19 Jun 2015 09:01:28 +1000 Subject: [PATCH] mm: kmemleak: allow safe memory scanning during kmemleak disabling 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. Change-Id: Idec67be116b23ee9aa56419e8f7c9e17df0086f2 Signed-off-by: Catalin Marinas Reported-by: Vignesh Radhakrishnan Tested-by: Vignesh Radhakrishnan Cc: Signed-off-by: Andrew Morton Git-commit: d613b66e1df80fddfff8e3eaa704243a955158db Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git Signed-off-by: Vignesh Radhakrishnan --- mm/kmemleak.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index bd417d126493..021a2f913baf 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -194,6 +194,8 @@ static struct kmem_cache *scan_area_cache; /* 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 */ @@ -951,7 +953,7 @@ 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); @@ -991,7 +993,7 @@ void __ref kmemleak_free_percpu(const void __percpu *ptr) 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)); @@ -1730,6 +1732,13 @@ 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; + if (!kmemleak_found_leaks) __kmemleak_do_cleanup(); else @@ -1756,6 +1765,8 @@ 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"); } @@ -1820,8 +1831,10 @@ 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); /*