Re: [PATCH 0/6] Fix deadlock in ftl formating on mtd

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Zhihao,

Zhihao Cheng <chengzhihao1@huawei.com> wrote on Sun, 13 Jun 2021
19:30:29 +0800:

> There is an AA-deadlock problem while formating mtd device to generate
> a ftl device. Fix it by reverting "mtd: allow to unload the mtdtrans
> module if its block devices aren't open" recommended in [1].
> 
> [<0>] blktrans_open+0x47/0x340            LOCK(mtd_table_mutex)
> [<0>] __blkdev_get+0x5b/0x3e0
> [<0>] blkdev_get_by_dev+0x18f/0x370
> [<0>] __device_add_disk+0x2db/0x700
> [<0>] device_add_disk+0x17/0x20
> [<0>] add_mtd_blktrans_dev+0x39e/0x6d0
> [<0>] ftl_add_mtd+0x792/0x908 [ftl]
> [<0>] register_mtd_blktrans+0xfb/0x170    LOCK(mtd_table_mutex)
> [<0>] ftl_tr_init+0x18/0x1000 [ftl]
> [<0>] do_one_initcall+0x71/0x330
> [<0>] do_init_module+0xa6/0x350
> 
> [1] http://lists.infradead.org/pipermail/linux-mtd/2017-March/072899.html
> 
> Zhihao Cheng (6):
>   Revert "mtd: blkdevs: fix potential deadlock + lockdep warnings"
>   Revert "mtd: fix: avoid race condition when accessing mtd->usecount"
>   Revert "mtd: mtd_blkdevs: don't increase 'open' count on error path"
>   Revert "mtd: mtd_blkdevs: fix error path in blktrans_open"
>   Revert "mtd: Remove redundant mutex from mtd_blkdevs.c"
>   Revert "mtd: allow to unload the mtdtrans module if its block devices
>     aren't open"

I understand that some fixes need to revert a couple of patches, but
isn't reverting 6 commits from the v2.6.32 kernel a bit odd for that?
At least, can you justify this choice? Are all these commits useless
and buggy?

> 
>  drivers/mtd/mtd_blkdevs.c | 77 +++++++++++++++------------------------
>  1 file changed, 30 insertions(+), 47 deletions(-)
> 

Thanks,
Miquèl