Micron qspi nor flash and UBIFS

[Richard Weinberger]

Andras,

On 01.09.2016 11:37, Andras Szemzo wrote:
> UBIFS (ubi0:0): background thread "ubifs_bgt0_0" started, PID 47
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1 at drivers/mtd/spi-nor/spi-nor.c:1177 spi_nor_write+0x57/0xea
> Writing at offset 128 into a NOR page. Writing partial pages may decrease reliability and increase wear of NOR flash.
> Modules linked in:
> CPU: 0 PID: 1 Comm: swapper Not tainted 4.8.0-rc2 #49
> Hardware name: Atmel SAMx7
> [<7000c5d9>] (unwind_backtrace) from [<7000b3ab>] (show_stack+0xb/0xc)
> [<7000b3ab>] (show_stack) from [<7000f095>] (__warn+0x89/0xb0)
> [<7000f095>] (__warn) from [<7000f0db>] (warn_slowpath_fmt+0x1f/0x28)
> [<7000f0db>] (warn_slowpath_fmt) from [<70127e8d>] (spi_nor_write+0x57/0xea)
> [<70127e8d>] (spi_nor_write) from [<70124593>] (part_write+0x27/0x2a)
> [<70124593>] (part_write) from [<70122717>] (mtd_write+0x53/0x68)
> [<70122717>] (mtd_write) from [<701301f3>] (ubi_io_write+0x23f/0x410)
> [<701301f3>] (ubi_io_write) from [<7012e0f7>] (ubi_eba_write_leb+0x77/0x5fc)
> [<7012e0f7>] (ubi_eba_write_leb) from [<7012d4c1>] (ubi_leb_write+0x71/0x8a)
> [<7012d4c1>] (ubi_leb_write) from [<7009dd9d>] (ubifs_leb_write+0x65/0xb4)
> [<7009dd9d>] (ubifs_leb_write) from [<7009edf3>] (ubifs_write_node+0xf7/0x124)
> [<7009edf3>] (ubifs_write_node) from [<700a2945>] (ubifs_write_master+0x91/0xc8)
> [<700a2945>] (ubifs_write_master) from [<7009c64f>] (ubifs_mount+0xebf/0x1020)
> [<7009c64f>] (ubifs_mount) from [<700555e9>] (mount_fs+0x9/0x60)
> [<700555e9>] (mount_fs) from [<7006427b>] (vfs_kern_mount+0x33/0xc0)
> [<7006427b>] (vfs_kern_mount) from [<700664c9>] (do_mount+0x599/0x788)
> [<700664c9>] (do_mount) from [<7006682b>] (SyS_mount+0x4f/0x6a)
> [<7006682b>] (SyS_mount) from [<702cd8d1>] (mount_block_root+0xa9/0x1e8)
> [<702cd8d1>] (mount_block_root) from [<702cdab1>] (prepare_namespace+0x4d/0xf0)
> [<702cdab1>] (prepare_namespace) from [<702cd731>] (kernel_init_freeable+0x105/0x14c)
> [<702cd731>] (kernel_init_freeable) from [<701c67db>] (kernel_init+0x7/0xa0)
> [<701c67db>] (kernel_init) from [<70009c49>] (ret_from_fork+0x11/0x28)

This proves my assumption.
spi-nor.c warns as soon you write with an offset to a page.
So, it will warn for *every* non-trivial user.

The warning is also rather new, CC'ing patch authors.

commit e5d05cbd6d8b01f08c95c427a36c66aac769af4f
Author: Michal Suchanek <hramrach at gmail.com>
Date:   Thu May 5 17:31:54 2016 -0700

    mtd: spi-nor: simplify write loop

    The spi-nor write loop assumes that what is passed to the hardware
    driver write() is what gets written.

    When write() writes less than page size at once data is dropped on the
    floor. Check the amount of data writen and exit if it does not match
    requested amount.

    Signed-off-by: Michal Suchanek <hramrach at gmail.com>
    Signed-off-by: Brian Norris <computersforpeace at gmail.com>
    Tested-by Cyrille Pitchen <cyrille.pitchen at atmel.com>
    Acked-by: Michal Suchanek <hramrach at gmail.com>
    Tested-by: Michal Suchanek <hramrach at gmail.com>


Guys, this patch is odd in multiple ways.
1. Patch description does not match the code. It does *not* just simplify the write loop.
   It also introduces a new scary WARN_ON_ONCE(). Unless I miss something it will trigger
   for every write with an offset. So, you rule out any filesystem on top of SPI-NOR.
   What's the deal?
2. The SOB chain is strange. Michal, you authored this patch, right?
   Why did you add an Acked-by and Tested-by tag too?

Thanks,
//richard