Re: [RESEND, PATCH 3/3] fuse: Add FOPEN_STREAM and use stream_open() if filesystem returned that from open handler

[Kirill Smelkov <kirr@nexedi.com>]

Hello up there,

On Wed, Apr 24, 2019 at 04:06:10PM +0000, Sasha Levin wrote:
> Hi,
>
> [This is an automated email]
>
> This commit has been processed because it contains a -stable tag.
> The stable tag indicates that it's relevant for the following trees: 3.14+
>
> The bot has tested the following trees: v5.0.9, v4.19.36, v4.14.113, v4.9.170, v4.4.178, v3.18.138.
>
> v5.0.9: Build failed! Errors:
>     fs/fuse/file.c:185:3: error: implicit declaration of function ‘stream_open’; did you mean ‘seq_open’? [-Werror=implicit-function-declaration]

This patch needs "fs: stream_open - opener for stream-like files so that
read and write can run simultaneously without deadlock" (10dce8af3422)
as its dependency. It documents so in its commit message. That base
dependency patch is being discussed here in stable context:

https://lore.kernel.org/linux-fsdevel/20190424183012.GB3798@deco.navytux.spb.ru/


> v4.19.36: Failed to apply! Possible dependencies:
>     6433b8998a21 ("fuse: add FOPEN_CACHE_DIR")
>     88bc7d5097a1 ("fuse: add support for copy_file_range()")

"fuse: add FOPEN_CACHE_DIR" added another nearby constant. The conflict
with that patch should be trivially resolvable (just add FOPEN_STREAM
irregardless that there is no FOPEN_CACHE_DIR in context).

> v4.14.113: Failed to apply! Possible dependencies:
>     3b7008b226f3 ("fuse: return -ECONNABORTED on /dev/fuse read after abort")
>     6433b8998a21 ("fuse: add FOPEN_CACHE_DIR")
>     88bc7d5097a1 ("fuse: add support for copy_file_range()")

same.

> v4.9.170: Failed to apply! Possible dependencies:
>     3b7008b226f3 ("fuse: return -ECONNABORTED on /dev/fuse read after abort")
>     6433b8998a21 ("fuse: add FOPEN_CACHE_DIR")
>     88bc7d5097a1 ("fuse: add support for copy_file_range()")

----//----

> v4.4.178: Failed to apply! Possible dependencies:
>     29433a2991fa ("fuse: get rid of fc->flags")
>     3767e255b390 ("switch ->setxattr() to passing dentry and inode separately")
>     60bcc88ad185 ("fuse: Add posix ACL support")
>     6192269444eb ("introduce a parallel variant of ->iterate()")
>     6433b8998a21 ("fuse: add FOPEN_CACHE_DIR")
>     6b2553918d8b ("replace ->follow_link() with new method that could stay in RCU mode")
>     703c73629f93 ("fuse: Use generic xattr ops")
>     84e710da2a1d ("parallel lookups machinery, part 2")
>     88bc7d5097a1 ("fuse: add support for copy_file_range()")
>     9902af79c01a ("parallel lookups: actual switch to rwsem")
>     9cf843e3f47c ("lookup_open(): lock the parent shared unless O_CREAT is given")
>     aa80deab33a8 ("namei: page_getlink() and page_follow_link_light() are the same thing")
>     cd3417c8fc95 ("kill free_page_put_link()")
>     ce23e6401334 ("->getxattr(): pass dentry and inode as separate arguments")
>     fceef393a538 ("switch ->get_link() to delayed_call, kill ->put_link()")

similar

> v3.18.138: Failed to apply! Possible dependencies:
>     09561a53b50d ("lustre: use %p[dD]")
>     29433a2991fa ("fuse: get rid of fc->flags")
>     2b0143b5c986 ("VFS: normal filesystems (and lustre): d_inode() annotations")
>     3767e255b390 ("switch ->setxattr() to passing dentry and inode separately")
>     60bcc88ad185 ("fuse: Add posix ACL support")
>     6192269444eb ("introduce a parallel variant of ->iterate()")
>     6433b8998a21 ("fuse: add FOPEN_CACHE_DIR")
>     680baacbca69 ("new ->follow_link() and ->put_link() calling conventions")
>     6b2553918d8b ("replace ->follow_link() with new method that could stay in RCU mode")
>     6e77137b363b ("don't pass nameidata to ->follow_link()")
>     703c73629f93 ("fuse: Use generic xattr ops")
>     84e710da2a1d ("parallel lookups machinery, part 2")
>     88bc7d5097a1 ("fuse: add support for copy_file_range()")
>     90e4fc8890da ("9p: don't bother with __getname() in ->follow_link()")
>     9902af79c01a ("parallel lookups: actual switch to rwsem")
>     9cf843e3f47c ("lookup_open(): lock the parent shared unless O_CREAT is given")
>     a06ae8609b3d ("coresight: add CoreSight core layer framework")
>     ce23e6401334 ("->getxattr(): pass dentry and inode as separate arguments")
>     dab363f938a5 ("Merge tag 'staging-3.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging")
>     fceef393a538 ("switch ->get_link() to delayed_call, kill ->put_link()")

similar

> How should we proceed with this patch?

I have backported this patch to above those stable trees. You can pull
the result from https://lab.nexedi.com/kirr/linux.git, branches:

	fopen_stream-5.0.y
	fopen_stream-4.19.y
	fopen_stream-4.14.y
	fopen_stream-4.4.y
		( actually fixed deadlock on /proc/xen/xenbus as
		  581d21a2d02a was not backported to 4.4 )
	fopen_stream-3.18.y
		( actually fixed deadlock on /proc/xen/xenbus as
		  581d21a2d02a was not backported to 3.18 )


Hope it helps a bit,

Kirill

P.S.

The fact that 4.4 and 3.18 versions of stream_open patch had to
resolve xenbus conflict in a way that actually fixes /proc/xen/xenbus
deadlock (introduced in 3.14) suggests that deadlock error messages
produced by stream_open.cocci should indeed be considered by relevant
maintainers including stable team...