Messages in this thread | | | Date | Wed, 6 May 2020 14:47:19 +0800 | From | Gao Xiang <> | Subject | Re: [f2fs-dev] [PATCH] f2fs: get parent inode when recovering pino |
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On Wed, May 06, 2020 at 09:58:22AM +0800, Gao Xiang wrote: > On Tue, May 05, 2020 at 06:24:28PM -0700, Eric Biggers wrote: > > On Wed, May 06, 2020 at 08:14:07AM +0800, Gao Xiang wrote: > > > > > > > > Actually, I think this is wrong because the fsync can be done via a file > > > > descriptor that was opened to a now-deleted link to the file. > > > > > > I'm still confused about this... > > > > > > I don't know what's wrong with this version from my limited knowledge? > > > inode itself is locked when fsyncing, so > > > > > > if the fsync inode->i_nlink == 1, this inode has only one hard link > > > (not deleted yet) and should belong to a single directory; and > > > > > > the only one parent directory would not go away (not deleted as well) > > > since there are some dirents in it (not empty). > > > > > > Could kindly explain more so I would learn more about this scenario? > > > Thanks a lot! > > > > i_nlink == 1 just means that there is one non-deleted link. There can be links > > that have since been deleted, and file descriptors can still be open to them. > > Thanks for your inspiration. You are right, thanks. > > Correct my words... I didn't check f2fs code just now, it seems f2fs doesn't > take inode_lock as some other fs like __generic_file_fsync or ubifs_fsync. > > And i_sem locks nlink / try_to_fix_pino similarly in some extent. It seems > no race by using d_find_alias here. Thanks again. >
(think more little bit just now...)
Thread 1: Thread 2 (fsync): vfs_unlink try_to_fix_pino f2fs_unlink f2fs_delete_entry f2fs_drop_nlink (i_sem, inode->i_nlink = 1)
(... but this dentry still hashed) i_sem, check inode->i_nlink = 1 i_sem d_find_alias
d_delete
I'm not sure if fsync could still use some wrong alias by chance.. completely untested, maybe just noise...
Thanks, Gao Xiang
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