Well, no suggestions from MM people? This is currently second top crasher
for syzbot and the reproducer is doing nothing special.
syzbot is reporting uninit-value at kmsan_handle_dma() in vring_map_one_sg().
----------
if (!vq->use_dma_api) {
/*
* If DMA is not used, KMSAN doesn't know that the scatterlist
* is initialized by the hardware. Explicitly check/unpoison it
* depending on the direction.
*/
kmsan_handle_dma(sg_page(sg), sg->offset, sg->length, direction);
*addr = (dma_addr_t)sg_phys(sg);
return 0;
}
----------
syzbot is reporting the page was allocated in ext4_da_write_begin().
----------
folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
mapping_gfp_mask(mapping));
if (IS_ERR(folio))
return PTR_ERR(folio);
/* In case writeback began while the folio was unlocked */
folio_wait_stable(folio);
#ifdef CONFIG_FS_ENCRYPTION
ret = ext4_block_write_begin(folio, pos, len, ext4_da_get_block_prep);
#else
ret = __block_write_begin(&folio->page, pos, len, ext4_da_get_block_prep);
#endif
----------
Since folio_wait_stable() calls folio_wait_writeback(), I'm guessing that
blk_mq_run_work_fn() is triggered by folio_wait_stable().
----------
void folio_wait_stable(struct folio *folio)
{
if (mapping_stable_writes(folio_mapping(folio)))
folio_wait_writeback(folio);
}
----------
If my guess is correct, I wonder how AS_STABLE_WRITES could be already set on a
folio struct returned by __filemap_get_folio() ? When AS_STABLE_WRITES is set?
Are there anything we can do for debugging this? Is adding a kernel config option that
does s/union/struct/g for helping debugger/printk() to inspect values in "struct folio"
possible?
Not directly related to this report, but I worry that
mapping_stable_writes(folio_mapping(folio)) might hit NULL pointer
dereference bug because folio_mapping() might return NULL and
mapping_stable_writes() assumes that the argument is not NULL.
On 2024/01/02 16:38, Tetsuo Handa wrote:
> #syz set subsystems: mm
>
> On 2024/01/01 22:38, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit: fbafc3e621c3 Merge tag 'for_linus' of git://git.kernel.org..
>> git tree: upstream
>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=173df3e9e80000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=e0c7078a6b901aa3
>> dashboard link: https://syzkaller.appspot.com/bug?extid=d7521c1e3841ed075a42
>> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1300b4a1e80000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=130b0379e80000
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/1520f7b6daa4/disk-fbafc3e6.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/8b490af009d5/vmlinux-fbafc3e6.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/202ca200f4a4/bzImage-fbafc3e6.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+d7521c1e3841ed075a42@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> =====================================================
>> BUG: KMSAN: uninit-value in vring_map_one_sg drivers/virtio/virtio_ring.c:380 [inline]
>> BUG: KMSAN: uninit-value in virtqueue_add_split drivers/virtio/virtio_ring.c:614 [inline]
>> BUG: KMSAN: uninit-value in virtqueue_add+0x21c6/0x6530 drivers/virtio/virtio_ring.c:2210
>> vring_map_one_sg drivers/virtio/virtio_ring.c:380 [inline]
>> virtqueue_add_split drivers/virtio/virtio_ring.c:614 [inline]
>> virtqueue_add+0x21c6/0x6530 drivers/virtio/virtio_ring.c:2210
>> virtqueue_add_sgs+0x186/0x1a0 drivers/virtio/virtio_ring.c:2244
>> __virtscsi_add_cmd drivers/scsi/virtio_scsi.c:467 [inline]
>> virtscsi_add_cmd+0x838/0xad0 drivers/scsi/virtio_scsi.c:501
>> virtscsi_queuecommand+0x896/0xa60 drivers/scsi/virtio_scsi.c:598
>> scsi_dispatch_cmd drivers/scsi/scsi_lib.c:1516 [inline]
>> scsi_queue_rq+0x4874/0x5790 drivers/scsi/scsi_lib.c:1758
>> blk_mq_dispatch_rq_list+0x13f8/0x3600 block/blk-mq.c:2049
>> __blk_mq_do_dispatch_sched block/blk-mq-sched.c:170 [inline]
>> blk_mq_do_dispatch_sched block/blk-mq-sched.c:184 [inline]
>> __blk_mq_sched_dispatch_requests+0x10af/0x2500 block/blk-mq-sched.c:309
>> blk_mq_sched_dispatch_requests+0x160/0x2d0 block/blk-mq-sched.c:333
>> blk_mq_run_work_fn+0xd0/0x280 block/blk-mq.c:2434
>> process_one_work kernel/workqueue.c:2627 [inline]
>> process_scheduled_works+0x104e/0x1e70 kernel/workqueue.c:2700
>> worker_thread+0xf45/0x1490 kernel/workqueue.c:2781
>> kthread+0x3ed/0x540 kernel/kthread.c:388
>> ret_from_fork+0x66/0x80 arch/x86/kernel/process.c:147
>> ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
>>
>> Uninit was created at:
>> __alloc_pages+0x9a4/0xe00 mm/page_alloc.c:4591
>> alloc_pages_mpol+0x62b/0x9d0 mm/mempolicy.c:2133
>> alloc_pages mm/mempolicy.c:2204 [inline]
>> folio_alloc+0x1da/0x380 mm/mempolicy.c:2211
>> filemap_alloc_folio+0xa5/0x430 mm/filemap.c:974
>> __filemap_get_folio+0xa5a/0x1760 mm/filemap.c:1918
>> ext4_da_write_begin+0x7f8/0xec0 fs/ext4/inode.c:2891
>> generic_perform_write+0x3f5/0xc40 mm/filemap.c:3918
>> ext4_buffered_write_iter+0x564/0xaa0 fs/ext4/file.c:299
>> ext4_file_write_iter+0x20f/0x3460
>> __kernel_write_iter+0x329/0x930 fs/read_write.c:517
>> dump_emit_page fs/coredump.c:888 [inline]
>> dump_user_range+0x593/0xcd0 fs/coredump.c:915
>> elf_core_dump+0x528d/0x5a40 fs/binfmt_elf.c:2077
>> do_coredump+0x32c9/0x4920 fs/coredump.c:764
>> get_signal+0x2185/0x2d10 kernel/signal.c:2890
>> arch_do_signal_or_restart+0x53/0xca0 arch/x86/kernel/signal.c:309
>> exit_to_user_mode_loop+0xe8/0x320 kernel/entry/common.c:168
>> exit_to_user_mode_prepare+0x163/0x220 kernel/entry/common.c:204
>> irqentry_exit_to_user_mode+0xd/0x30 kernel/entry/common.c:309
>> irqentry_exit+0x16/0x40 kernel/entry/common.c:412
>> exc_page_fault+0x246/0x6f0 arch/x86/mm/fault.c:1564
>> asm_exc_page_fault+0x2b/0x30 arch/x86/include/asm/idtentry.h:570
>>
>> Bytes 0-4095 of 4096 are uninitialized
>> Memory access of size 4096 starts at ffff88812c79c000
>>
>> CPU: 0 PID: 997 Comm: kworker/0:1H Not tainted 6.7.0-rc7-syzkaller-00003-gfbafc3e621c3 #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
>> Workqueue: kblockd blk_mq_run_work_fn
>> =====================================================
>
