On Wed, 2018-12-19 at 16:27 -0700, Jens Axboe wrote: > On 12/19/18 4:24 PM, Bart Van Assche wrote: > > Hello, > > > > If I run the srp blktests in a loop then I see the below call stack > > appearing > > sporadically. I have not yet had the time to analyze this but I'm reporting > > this here in case someone else would already have had a look at this. > > > > Bart. > > > > ================================================================== > > BUG: KASAN: use-after-free in bt_iter+0x86/0xf0 > > Read of size 8 at addr ffff88803b335240 by task fio/21412 > > > > CPU: 0 PID: 21412 Comm: fio Tainted: G W 4.20.0-rc6-dbg+ #3 > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 > > 04/01/2014 > > Call Trace: > > dump_stack+0x86/0xca > > print_address_description+0x71/0x239 > > kasan_report.cold.5+0x242/0x301 > > __asan_load8+0x54/0x90 > > bt_iter+0x86/0xf0 > > blk_mq_queue_tag_busy_iter+0x373/0x5e0 > > blk_mq_in_flight+0x96/0xb0 > > part_in_flight+0x40/0x140 > > part_round_stats+0x18e/0x370 > > blk_account_io_start+0x3d7/0x670 > > blk_mq_bio_to_request+0x19c/0x3a0 > > blk_mq_make_request+0x7a9/0xcb0 > > generic_make_request+0x41d/0x960 > > submit_bio+0x9b/0x250 > > do_blockdev_direct_IO+0x435c/0x4c70 > > __blockdev_direct_IO+0x79/0x88 > > ext4_direct_IO+0x46c/0xc00 > > generic_file_direct_write+0x119/0x210 > > __generic_file_write_iter+0x11c/0x280 > > ext4_file_write_iter+0x1b8/0x6f0 > > aio_write+0x204/0x310 > > io_submit_one+0x9d3/0xe80 > > __x64_sys_io_submit+0x115/0x340 > > do_syscall_64+0x71/0x210 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > RIP: 0033:0x7f02cf043219 > > I've seen this one before as well, it's not a new thing. As far as I can > tell, it's a false positive. There should be no possibility for a > use-after-free iterating the static tags/requests.
Are you sure this is a false positive? I have not yet encountered any false positive KASAN complaints. According to the following gdb output this complaint refers to reading rq->q: (gdb) list *(bt_iter+0x86) 0xffffffff816b9346 is in bt_iter (block/blk-mq-tag.c:237). 232 233 /* 234 * We can hit rq == NULL here, because the tagging functions 235 * test and set the bit before assigning ->rqs[]. 236 */ 237 if (rq && rq->q == hctx->queue) 238 iter_data->fn(hctx, rq, iter_data->data, reserved); 239 return true; 240 } 241 >From the disassembly output: 232 233 /* 234 * We can hit rq == NULL here, because the tagging functions 235 * test and set the bit before assigning ->rqs[]. 236 */ 237 if (rq && rq->q == hctx->queue) 0xffffffff816b9339 <+121>: test %r12,%r12 0xffffffff816b933c <+124>: je 0xffffffff816b935f <bt_iter+159> 0xffffffff816b933e <+126>: mov %r12,%rdi 0xffffffff816b9341 <+129>: callq 0xffffffff813bd3e0 <__asan_load8> 0xffffffff816b9346 <+134>: lea 0x138(%r13),%rdi 0xffffffff816b934d <+141>: mov (%r12),%r14 0xffffffff816b9351 <+145>: callq 0xffffffff813bd3e0 <__asan_load8> 0xffffffff816b9356 <+150>: cmp 0x138(%r13),%r14 0xffffffff816b935d <+157>: je 0xffffffff816b936f <bt_iter+175> BTW, rq may but does not have to refer to tags->static_rqs[...]. It may also refer to hctx->fq.flush_rq. Bart.
