[PATCH v2] erofs: check the uniqueness of fsid in shared domain in advance

[Chao Yu]

On 2022/11/25 19:08, Hou Tao wrote:
> From: Hou Tao <houtao1 at huawei.com>
> 
> When shared domain is enabled, doing mount twice with the same fsid and
> domain_id will trigger sysfs warning as shown below:
> 
>   sysfs: cannot create duplicate filename '/fs/erofs/d0,meta.bin'
>   CPU: 15 PID: 1051 Comm: mount Not tainted 6.1.0-rc6+ #1
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
>   Call Trace:
>    <TASK>
>    dump_stack_lvl+0x38/0x49
>    dump_stack+0x10/0x12
>    sysfs_warn_dup.cold+0x17/0x27
>    sysfs_create_dir_ns+0xb8/0xd0
>    kobject_add_internal+0xb1/0x240
>    kobject_init_and_add+0x71/0xa0
>    erofs_register_sysfs+0x89/0x110
>    erofs_fc_fill_super+0x98c/0xaf0
>    vfs_get_super+0x7d/0x100
>    get_tree_nodev+0x16/0x20
>    erofs_fc_get_tree+0x20/0x30
>    vfs_get_tree+0x24/0xb0
>    path_mount+0x2fa/0xa90
>    do_mount+0x7c/0xa0
>    __x64_sys_mount+0x8b/0xe0
>    do_syscall_64+0x30/0x60
>    entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> The reason is erofs_fscache_register_cookie() doesn't guarantee the primary
> data blob (aka fsid) is unique in the shared domain and
> erofs_register_sysfs() invoked by the second mount will fail due to the
> duplicated fsid in the shared domain and report warning.
> 
> It would be better to check the uniqueness of fsid before doing
> erofs_register_sysfs(), so adding a new flags parameter for
> erofs_fscache_register_cookie() and doing the uniqueness check if
> EROFS_REG_COOKIE_NEED_NOEXIST is enabled.
> 
> After the patch, the error in dmesg for the duplicated mount would be:
> 
>   erofs: ...: erofs_domain_register_cookie: XX already exists in domain YY
> 
> Reviewed-by: Jia Zhu <zhujia.zj at bytedance.com>
> Signed-off-by: Hou Tao <houtao1 at huawei.com>

Reviewed-by: Chao Yu <chao at kernel.org>

Thanks,