Re: [PATCH v7 0/3] md/raid10: fix r10bio width mismatches across reshape

[Chen Cheng]

On 2026/7/27 18:54, Mykola Marzhan wrote:
> Hi Cheng,
> 
> Here are the test results I promised. v7 fixes it.
> 
> I used one kernel tree, rebuilt incrementally between the two builds,
> so the only difference is your three patches. The array is raid10 n2
> with 4 members. The load is four fio jobs: 4k randwrite, O_DIRECT,
> iodepth 32. While the load runs, I --add two spares and then
> --grow --raid-devices=6. The kernel is KASAN generic with
> kasan_multi_shot. Each run is 5 cycles:
> 
>    kernel      runs  cycles  grows completed  slab-out-of-bounds
>    base           1       5             5/5   128 (in 4 of 5 cycles)
>    base + v7      2   5 + 5           10/10     0
> 
> All 128 base reports are in free_r10bio(): 64 reads and 64 writes,
> each of 8 bytes. There is also a second report site,
> raid10_make_request(). A warm-up run on the same base hit it too,
> with 2 slab-out-of-bounds there alongside 568 in free_r10bio(). So
> both report sites are reachable with this workload.
> 
> Every cycle on both kernels logged "md: md0: reshape done." and the
> same capacity change, so the grow really did run 10/10 on the patched
> kernel, and fio was alive throughout each cycle.
> 
> The bug does not fire in every cycle: per-cycle counts on the base
> were 0, 40, 8, 56, 24, so the base hit it in 4 of 5 cycles. That rate
> is what gives the patched 10/10 zero its meaning.
> 
> Tested-by: Mykola Marzhan <mykola@xxxxxxxxxxx>
> 

Hi Mykola,

I see, really thanks for your test result!

> One practical note: v7 does not apply to mainline. Patch 2/3 carries
> context
> 
>    static void __make_request(struct mddev *mddev, struct bio *bio, int sectors)
> 
> but e045d6ed33f8 ("md/raid10: fix writes_pending leak on write request
> failures") changed __make_request() to return bool. Applying
> 1/3..3/3 with --fuzz=0:
> 
>    8e065a160251 (= e045d6ed33f8^)        applies clean
>    e045d6ed33f8                          fails
>    55b77337bdd0                          fails
>    v7.2-rc4                              fails
>    current mainline                      fails
> 

Got it, I must misuse a unclean branch.

> So the numbers above are from 8e065a160251, which is the newest base v7
> applies to. A rebase would probably help it get picked up — happy to
> re-run the same rig on a v8 if you post one.
> 

I don't want to waste your time, I would re-run reproducer before I send.

Reproducer Link: 
https://github.com/chencheng-fnnas/reproducer/blob/main/repro-raid10-4to5-reshape-r10bio-oob.sh

Thanks again,
Cheng.

> Thanks,
> Mykola