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. -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg -- 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
