Messages in this thread | | | Date | Tue, 13 Sep 2022 12:52:41 +0800 | Subject | Re: [External] Re: [PATCH V2 4/5] erofs: remove duplicated unregister_cookie | From | Jia Zhu <> |
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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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