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SubjectRe: dm: Forbid requeue of writes to zones
Date
On 2021/06/04 7:17, Colin Ian King wrote:
> Hi,
>
> Static analysis with Coverity on Linux next has found and issue in
> drivers/md/dm.c with the following commit:
>
> commit 2c243153d1d4be4e23735cd10984ac17c7a54531
> Author: Damien Le Moal <damien.lemoal@wdc.com>
> Date: Wed May 26 06:24:58 2021 +0900
>
> dm: Forbid requeue of writes to zones
>
> The analysis is as follows:
>
> 828 static void dec_pending(struct dm_io *io, blk_status_t error)
> 829 {
> 830 unsigned long flags;
> 831 blk_status_t io_error;
>
> 1. var_decl: Declaring variable bio without initializer.

This one is related to #7.

>
> 832 struct bio *bio;
> 833 struct mapped_device *md = io->md;
> 834
> 835 /* Push-back supersedes any I/O errors */
>
> 2. Condition !!error, taking true branch.
>
> 836 if (unlikely(error)) {
> 837 spin_lock_irqsave(&io->endio_lock, flags);
>
> 3. Condition io->status == 11 /* (blk_status_t)11 */, taking false
> branch.
>
> 838 if (!(io->status == BLK_STS_DM_REQUEUE &&
> __noflush_suspending(md)))
> 839 io->status = error;
> 840 spin_unlock_irqrestore(&io->endio_lock, flags);
> 841 }
> 842

My patch does not touch these hunks. They are as is. So that is not new.

>
> 4. Condition atomic_dec_and_test(&io->io_count), taking true branch.
>
> 843 if (atomic_dec_and_test(&io->io_count)) {
>
> 5. Condition io->status == 11 /* (blk_status_t)11 */, taking true
> branch.
>
> 844 if (io->status == BLK_STS_DM_REQUEUE) {
> 845 /*
> 846 * Target requested pushing back the I/O.
> 847 */
> 848 spin_lock_irqsave(&md->deferred_lock, flags);
>
> 6. Condition __noflush_suspending(md), taking true branch.
>
> 849 if (__noflush_suspending(md) &&

I do not understand this one, nor #4.

>
> Uninitialized pointer read
> 7. uninit_use_in_call: Using uninitialized value bio when calling
> dm_is_zone_write.
>
> 850 !WARN_ON_ONCE(dm_is_zone_write(md, bio)))
> 851 /* NOTE early return due to
> BLK_STS_DM_REQUEUE below */
> 852 bio_list_add_head(&md->deferred,
> io->orig_bio);

The kernel build robot signaled this one already. Will send an incremental patch
asap today.

>
> The pointer bio is not initialized and yet is being used in the call to
> function dm_is_zone_write where pointer bio is being accessed. I'm not
> sure what the original intent was, but this looks incorrect.
>
> Colin
>


--
Damien Le Moal
Western Digital Research

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