configfs: Fix symlink() to a removing item
PATCH 1/1 configfs: Fix symlink() to a removing item
Hi, the following patch fixes the symlink bug I mentioned a few days ago. Thanks for your comments.
Louis
Signature · 18 lines
Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes -------------- next part -------------- A non-text attachment was scrubbed... Name: configfs-do-not-symlink-to-removing-item.patch Type: text/x-diff Size: 3385 bytes Desc: not available Url : http://oss.oracle.com/pipermail/ocfs2-devel/attachments/20080616/468a2f8f/attachment.bin -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 189 bytes Desc: Digital signature Url : http://oss.oracle.com/pipermail/ocfs2-devel/attachments/20080616/468a2f8f/attachment-0001.bin
Quoted 8 lines · Louis Rilling
This patch introduces a similar (weird?) behavior as with mkdir failures making rmdir fail: if
symlink()races withrmdir()of the parent directory (or its youngest user-created ancestor if parent is a default group) orrmdir()of the target directory, and then fails inconfigfs_create(), this can make the racingrmdir()fail despite the concerned directory having no user-created entry (resp. no symlink pointing to it or one of its default groups) in the end. If this behavior is found unacceptable, I'll submit a fix in the same spirit as the racingmkdir()fix.
Ahh, but you can't wait on the mutex like you do in mkdir(),
because they're not ordered - it can race rename again.
Joel
Signature · 9 lines
Dort wo man B?cher verbrennt, verbrennt man am Ende auch Mensch. (Wherever they burn books, they will also end up burning people.) - Heinrich Heine Joel Becker Principal Software Developer Oracle E-mail: joel.becker at oracle.com Phone: (650) 506-8127
Quoted 10 lines · Joel Becker
Quoted 8 lines · Louis Rilling
This patch introduces a similar (weird?) behavior as with mkdir failures making rmdir fail: if
symlink()races withrmdir()of the parent directory (or its youngest user-created ancestor if parent is a default group) orrmdir()of the target directory, and then fails inconfigfs_create(), this can make the racingrmdir()fail despite the concerned directory having no user-created entry (resp. no symlink pointing to it or one of its default groups) in the end. If this behavior is found unacceptable, I'll submit a fix in the same spirit as the racingmkdir()fix.
Quoted 2 lines
Ahh, but you can't wait on the mutex like you do in
mkdir(),
because they're not ordered - it can race rename again.
Yes I can. In the mkdir() case, rmdir() waits on the mutex of one of the default groups. The symlink case will be handled the same. The difference is that while mkdir() tags the parent with CONFIGFS_USET_IN_MKDIR, symlink() will tag both the parent and the target with CONFIGFS_USET_IN_SYMLINK. [ We can actually merge the two flags in something like CONFIGFS_USET_ATTACHING. ] Since tagging requires only to take configfs_dirent_lock, there will be no deadlock.
I'll send a patch later.
Louis
Signature · 11 lines
Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 189 bytes Desc: Digital signature Url : http://oss.oracle.com/pipermail/ocfs2-devel/attachments/20080617/42ecb234/attachment.bin
Quoted 14 lines · Louis Rilling
Quoted 10 lines · Joel Becker
Quoted 8 lines · Louis Rilling
This patch introduces a similar (weird?) behavior as with mkdir failures making rmdir fail: if
symlink()races withrmdir()of the parent directory (or its youngest user-created ancestor if parent is a default group) orrmdir()of the target directory, and then fails inconfigfs_create(), this can make the racingrmdir()fail despite the concerned directory having no user-created entry (resp. no symlink pointing to it or one of its default groups) in the end. If this behavior is found unacceptable, I'll submit a fix in the same spirit as the racingmkdir()fix.Quoted 2 lines
Ahh, but you can't wait on the mutex like you do in
mkdir(),
because they're not ordered - it can race rename again.
Quoted 6 lines
Yes I can. In the
mkdir()case,rmdir()waits on the mutex of one of the default groups. The symlink case will be handled the same. The difference is that whilemkdir()tags the parent withCONFIGFS_USET_IN_MKDIR,symlink()will tag both the parent and the target withCONFIGFS_USET_IN_SYMLINK. [ We can actually merge the two flags in something likeCONFIGFS_USET_ATTACHING. ] Since tagging requires only to takeconfigfs_dirent_lock, there will be no deadlock.
Hm, you were right, sorry. We can only solve the race with rmdir() removing the item where the symlink is created. For the target item, I don't know yet...
Louis
Signature · 11 lines
Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 189 bytes Desc: Digital signature Url : http://oss.oracle.com/pipermail/ocfs2-devel/attachments/20080617/bd80833f/attachment-0001.bin