linux-kernel - Re: [PATCH v2] erofs: check the uniqueness of fsid in shared domain in advance

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Date:   Sat, 26 Nov 2022 11:20:49 +0800
From:   Jingbo Xu <jefflexu@...ux.alibaba.com>
To:     Hou Tao <houtao@...weicloud.com>, linux-erofs@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, Gao Xiang <xiang@...nel.org>,
        Chao Yu <chao@...nel.org>, Yue Hu <huyue2@...lpad.com>,
        Jia Zhu <zhujia.zj@...edance.com>, houtao1@...wei.com
Subject: Re: [PATCH v2] erofs: check the uniqueness of fsid in shared domain
 in advance

Hi Tao,

Thanks for catching this!


On 11/25/22 7:08 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@...wei.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@...edance.com>
> Signed-off-by: Hou Tao <houtao1@...wei.com>

LGTM.

Reviewed-by: Jingbo Xu <jefflexu@...ux.alibaba.com>


-- 
Thanks,
Jingbo