On 01/23/2017 09:17 AM, Alexander Potapenko wrote: > On Mon, Jan 23, 2017 at 5:03 PM, Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> wrote: >> 2017-01-23 17:06 GMT+03:00 Alexander Potapenko <glider@xxxxxxxxxx>: >>> KMSAN (KernelMemorySanitizer, a new error detection tool) reports use of >>> uninitialized memory in cfq_init_cfqq(): >>> >>> ================================================================== >>> BUG: KMSAN: use of unitialized memory >>> ... >>> Call Trace: >>> [< inline >] __dump_stack lib/dump_stack.c:15 >>> [<ffffffff8202ac97>] dump_stack+0x157/0x1d0 lib/dump_stack.c:51 >>> [<ffffffff813e9b65>] kmsan_report+0x205/0x360 ??:? >>> [<ffffffff813eabbb>] __msan_warning+0x5b/0xb0 ??:? >>> [< inline >] cfq_init_cfqq block/cfq-iosched.c:3754 >>> [<ffffffff8201e110>] cfq_get_queue+0xc80/0x14d0 block/cfq-iosched.c:3857 >>> ... >>> origin: >>> [<ffffffff8103ab37>] save_stack_trace+0x27/0x50 arch/x86/kernel/stacktrace.c:67 >>> [<ffffffff813e836b>] kmsan_internal_poison_shadow+0xab/0x150 ??:? >>> [<ffffffff813e88ab>] kmsan_poison_slab+0xbb/0x120 ??:? >>> [< inline >] allocate_slab mm/slub.c:1627 >>> [<ffffffff813e533f>] new_slab+0x3af/0x4b0 mm/slub.c:1641 >>> [< inline >] new_slab_objects mm/slub.c:2407 >>> [<ffffffff813e0ef3>] ___slab_alloc+0x323/0x4a0 mm/slub.c:2564 >>> [< inline >] __slab_alloc mm/slub.c:2606 >>> [< inline >] slab_alloc_node mm/slub.c:2669 >>> [<ffffffff813dfb42>] kmem_cache_alloc_node+0x1d2/0x1f0 mm/slub.c:2746 >>> [<ffffffff8201d90d>] cfq_get_queue+0x47d/0x14d0 block/cfq-iosched.c:3850 >>> ... >>> ================================================================== >>> (the line numbers are relative to 4.8-rc6, but the bug persists >>> upstream) >>> >>> The uninitialized struct cfq_queue is created by kmem_cache_alloc_node() >>> and then passed to cfq_init_cfqq(), which accesses cfqq->ioprio_class >>> before it's initialized. >>> >> >> struct cfq_queue is zero initialized (__GFP_ZERO). >> The warning is false-positive. > You are totally right. I've handled __GFP_ZERO in (hopefully) every > case except for this one, and overlooked the presence of that flag in > the kmem_cache_alloc_node(). > Thanks for double-checking! > Jens, sorry for the false alarm. No worries, I did queue up the patch, since even if it is a false positive, it's cleaner to set this explicitly to NONE rather than silently rely on the fact that NONE is 0. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
