4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Vinayak Menon <[email protected]> [ Upstream commit 914b6dfff790544d9b77dfd1723adb3745ec9700 ] A crash is observed when kmemleak_scan accesses the object->pointer, likely due to the following race. TASK A TASK B TASK C kmemleak_write (with "scan" and NOT "scan=on") kmemleak_scan() create_object kmem_cache_alloc fails kmemleak_disable kmemleak_do_cleanup kmemleak_free_enabled = 0 kfree kmemleak_free bails out (kmemleak_free_enabled is 0) slub frees object->pointer update_checksum crash - object->pointer freed (DEBUG_PAGEALLOC) kmemleak_do_cleanup waits for the scan thread to complete, but not for direct call to kmemleak_scan via kmemleak_write. So add a wait for kmemleak_scan completion before disabling kmemleak_free, and while at it fix the comment on stop_scan_thread. [[email protected]: fix stop_scan_thread comment] Link: http://lkml.kernel.org/r/[email protected] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Vinayak Menon <[email protected]> Reviewed-by: Catalin Marinas <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- mm/kmemleak.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1524,8 +1524,7 @@ static void start_scan_thread(void) } /* - * Stop the automatic memory scanning thread. This function must be called - * with the scan_mutex held. + * Stop the automatic memory scanning thread. */ static void stop_scan_thread(void) { @@ -1788,12 +1787,15 @@ static void kmemleak_do_cleanup(struct w { stop_scan_thread(); + mutex_lock(&scan_mutex); /* - * 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. + * Once it is made sure that kmemleak_scan 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; + mutex_unlock(&scan_mutex); if (!kmemleak_found_leaks) __kmemleak_do_cleanup();
