[PATCH] mtd: core: Fix ERROR of refcount due to del_mtd_device()

[Miquel Raynal]

On Sat, 2022-11-19 at 06:39:15 UTC, Shang XiaoJing wrote:
> del_mtd_device() will call of_node_put() to mtd_get_of_node(mtd), which
> is mtd->dev.of_node. However, memset(&mtd->dev, 0) is called before
> of_node_put(). As the result, of_node_put() won't do anything in
> del_mtd_device(), and causes the refcount leak.
> 
> del_mtd_device()
>     memset(&mtd->dev, 0, sizeof(mtd->dev) # clear mtd->dev
>     of_node_put()
>         mtd_get_of_node(mtd) # mtd->dev is cleared, can't locate of_node
>                              # of_node_put(NULL) won't do anything
> 
> Fix the ERROR by caching the pointer of the device_node.
> 
> OF: ERROR: memory leak, expected refcount 1 instead of 2,
> of_node_get()/of_node_put() unbalanced - destroy cset entry: attach
> overlay node /spi/spi-sram at 0
> CPU: 3 PID: 275 Comm: python3 Tainted: G N 6.1.0-rc3+ #54
>     0d8a1edddf51f172ff5226989a7565c6313b08e2
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
> Call Trace:
> <TASK>
>     dump_stack_lvl+0x67/0x83
>     kobject_get+0x155/0x160
>     of_node_get+0x1f/0x30
>     of_fwnode_get+0x43/0x70
>     fwnode_handle_get+0x54/0x80
>     fwnode_get_nth_parent+0xc9/0xe0
>     fwnode_full_name_string+0x3f/0xa0
>     device_node_string+0x30f/0x750
>     pointer+0x598/0x7a0
>     vsnprintf+0x62d/0x9b0
>     ...
>     cfs_overlay_release+0x30/0x90
>     config_item_release+0xbe/0x1a0
>     config_item_put+0x5e/0x80
>     configfs_rmdir+0x3bd/0x540
>     vfs_rmdir+0x18c/0x320
>     do_rmdir+0x198/0x330
>     __x64_sys_rmdir+0x2c/0x40
>     do_syscall_64+0x37/0x90
>     entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Fixes: 00596576a051 ("mtd: core: clear out unregistered devices a bit more")
> Signed-off-by: Shang XiaoJing <shangxiaojing at huawei.com>

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git mtd/next, thanks.

Miquel