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SubjectRe: [External] Re: [PATCH V2 4/5] erofs: remove duplicated unregister_cookie
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在 2022/9/9 18:28, JeffleXu 写道:
>
>
> On 9/9/22 5:55 PM, JeffleXu wrote:
>>
>>
>> On 9/2/22 6:53 PM, Jia Zhu wrote:
>>> In erofs umount scenario, erofs_fscache_unregister_cookie() is called
>>> twice in kill_sb() and put_super().
>>>
>>> It works for original semantics, cause 'ctx' will be set to NULL in
>>> put_super() and will not be unregister again in kill_sb().
>>> However, in shared domain scenario, we use refcount to maintain the
>>> lifecycle of cookie. Unregister the cookie twice will cause it to be
>>> released early.
>
> Sorry, why can't we also set sbi->s_fscache to NULL after decrementing
> the refcount in shared domain mode, to avoid the refcount being
> decremented twice?
>
In below case:
1. mount -t erofs none -o fsid=bootstrap.img -o device=blob.img -o
domain_id=1 mnt
2. mount -t erofs none -o fsid=bootstrap.img -o device=blob.img -o
domain_id=1 mnt2
3. Procedure 2 will fail since we can't mount erofs with the same sysfs
entry.
4. Mount()'s error handling path will step into put_super().
5. Domain's refcnt will be decremented even if it has not yet
been incremented.
>>>
>>> For the above reasons, this patch removes duplicate unregister_cookie
>>> and move fscache_unregister_* before shotdown_super() to prevent busy
>>> inode(ctx->inode) when umount.
>>>
>>> Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
>>> ---
>>> fs/erofs/super.c | 16 ++++++++--------
>>> 1 file changed, 8 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>>> index 69de1731f454..667a78f0ee70 100644
>>> --- a/fs/erofs/super.c
>>> +++ b/fs/erofs/super.c
>>> @@ -919,19 +919,20 @@ static void erofs_kill_sb(struct super_block *sb)
>>> kill_litter_super(sb);
>>> return;
>>> }
>>> - if (erofs_is_fscache_mode(sb))
>>> - generic_shutdown_super(sb);
>>> - else
>>> - kill_block_super(sb);
>>> -
>>> sbi = EROFS_SB(sb);
>>> if (!sbi)
>>> return;
>>>
>>> + if (erofs_is_fscache_mode(sb)) {
>>> + erofs_fscache_unregister_cookie(&sbi->s_fscache);
>>> + erofs_fscache_unregister_fs(sb);
>>> + generic_shutdown_super(sb);
>>
>> Generally we can't do clean ups before generic_shutdown_super(), since
>> generic_shutdown_super() may trigger IO, e.g. in sync_filesystem(),
>> though it's not the case for erofs (read-only).
>>
>> How about embedding erofs_fscache_unregister_cookie() into
>> erofs_fscache_unregister_fs(), and thus we can check domain_id in
>> erofs_fscache_unregister_fs()?
>>
>>> + } else {
>>> + kill_block_super(sb);
>>> + }
>>> +
>>> erofs_free_dev_context(sbi->devs);
>>> fs_put_dax(sbi->dax_dev, NULL);
>>> - erofs_fscache_unregister_cookie(&sbi->s_fscache);
>>> - erofs_fscache_unregister_fs(sb);
>>> kfree(sbi->opt.fsid);
>>> kfree(sbi->opt.domain_id);
>>> kfree(sbi);
>>> @@ -951,7 +952,6 @@ static void erofs_put_super(struct super_block *sb)
>>> iput(sbi->managed_cache);
>>> sbi->managed_cache = NULL;
>>> #endif
>>> - erofs_fscache_unregister_cookie(&sbi->s_fscache);
>>> }
>>>
>>> struct file_system_type erofs_fs_type = {
>>
>

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