linux-next test error: KASAN: stack-out-of-bounds Read in bio_alloc_bioset

[syzbot <syzbot+bf04628c1f6179269b0b@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    d37d5704 Add linux-next specific files for 20200702
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1549d0a3100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a0a0972a399422ff
dashboard link: https://syzkaller.appspot.com/bug?extid=bf04628c1f6179269b0b
compiler:       gcc (GCC) 10.1.0-syz 20200507

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+bf04628c1f6179269b0b@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: stack-out-of-bounds in bio_list_empty include/linux/bio.h:561 [inline]
BUG: KASAN: stack-out-of-bounds in bio_alloc_bioset+0x5b2/0x5d0 block/bio.c:482
Read of size 8 at addr ffffc90000fc7150 by task kworker/u4:4/169

CPU: 0 PID: 169 Comm: kworker/u4:4 Not tainted 5.8.0-rc3-next-20200702-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0x5/0x436 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 bio_list_empty include/linux/bio.h:561 [inline]
 bio_alloc_bioset+0x5b2/0x5d0 block/bio.c:482
 bio_clone_fast+0x21/0x1b0 block/bio.c:710
 bio_split+0xc7/0x2c0 block/bio.c:1477
 blk_bio_segment_split block/blk-merge.c:281 [inline]
 __blk_queue_split+0x10e2/0x1650 block/blk-merge.c:331
 blk_mq_submit_bio+0x1b0/0x1760 block/blk-mq.c:2169
 __submit_bio_noacct_mq block/blk-core.c:1181 [inline]
 submit_bio_noacct+0xc9e/0x12d0 block/blk-core.c:1214
 submit_bio+0x263/0x5b0 block/blk-core.c:1284
 ext4_io_submit fs/ext4/page-io.c:382 [inline]
 io_submit_add_bh fs/ext4/page-io.c:423 [inline]
 ext4_bio_write_page+0x9a8/0x1c27 fs/ext4/page-io.c:550
 mpage_submit_page+0x140/0x2c0 fs/ext4/inode.c:2082
 mpage_map_and_submit_buffers fs/ext4/inode.c:2330 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2469 [inline]
 ext4_writepages+0x237e/0x3960 fs/ext4/inode.c:2782
 do_writepages+0xec/0x290 mm/page-writeback.c:2352
 __writeback_single_inode+0x125/0x1400 fs/fs-writeback.c:1461
 writeback_sb_inodes+0x53d/0xf40 fs/fs-writeback.c:1721
 __writeback_inodes_wb+0xc6/0x280 fs/fs-writeback.c:1790
 wb_writeback+0x8bb/0xd40 fs/fs-writeback.c:1896
 wb_check_background_flush fs/fs-writeback.c:1964 [inline]
 wb_do_writeback fs/fs-writeback.c:2052 [inline]
 wb_workfn+0xb20/0x13e0 fs/fs-writeback.c:2080
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294


addr ffffc90000fc7150 is located in stack of task kworker/u4:4/169 at offset 80 in frame:
 arch_atomic64_read arch/x86/include/asm/atomic64_64.h:22 [inline]
 arch_atomic64_fetch_add_unless include/linux/atomic-arch-fallback.h:2195 [inline]
 arch_atomic64_add_unless include/linux/atomic-arch-fallback.h:2220 [inline]
 arch_atomic64_inc_not_zero include/linux/atomic-arch-fallback.h:2236 [inline]
 atomic64_inc_not_zero include/asm-generic/atomic-instrumented.h:1609 [inline]
 atomic_long_inc_not_zero include/asm-generic/atomic-long.h:497 [inline]
 percpu_ref_tryget_live include/linux/percpu-refcount.h:282 [inline]
 submit_bio_noacct+0x0/0x12d0 block/blk-core.c:433

this frame has 3 objects:
 [32, 40) 'bio'
 [64, 80) 'bio_list'
 [96, 128) 'bio_list_on_stack'

Memory state around the buggy address:
 ffffc90000fc7000: 00 00 00 f2 f2 f2 00 00 00 00 00 f3 f3 f3 f3 f3
 ffffc90000fc7080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc90000fc7100: f1 f1 f1 f1 00 f2 f2 f2 00 00 f2 f2 00 00 00 00
                                                 ^
 ffffc90000fc7180: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90000fc7200: 00 00 00 f1 f1 f1 f1 00 f2 f2 f2 00 00 00 00 f3
==================================================================


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