Hello stable team,
Please consider applying the following 2 patches to Linux-3.18 stable
tree. The patches fix regression introduced in 3.14 where both read and
write started to run under lock taken, which resulted in FUSE (and many
other drivers) deadlocks for cases where stream-like files are used with
read and write being run simultaneously.
Please see complete problem description in upstream commit 10dce8af3422
("fs: stream_open - opener for stream-like files so that read and write
can run simultaneously without deadlock").
The actual FUSE fix (upstream commit bbd84f33652f "fuse: Add
FOPEN_STREAM to use stream_open()") was merged into 5.2 with `Cc:
[email protected] # v3.14+` mark and is already included into 5.1,
5.0 and 4.19 stable trees. However for some reason it is not (yet ?)
included into 4.14, 4.9, 4.4, 3.18 and 3.16 trees.
The patches fix a real problem into which my FUSE filesystem ran, and
which also likely affects OSSPD (full details are in the patches
description). Please consider including the fixes into 3.18 (as well as
into other stable trees - I'm sending corresponding series separately -
- one per tree).
Thanks beforehand,
Kirill
P.S. the patches have been already a bit discussed in stable context some
time ago:
https://lore.kernel.org/linux-fsdevel/CAHk-=wgh234SyBG810=vB360PCzVkAhQRqGg8aFdATZd+daCFw@mail.gmail.com/
https://lore.kernel.org/linux-fsdevel/[email protected]/
https://lore.kernel.org/linux-fsdevel/[email protected]/
...
Kirill Smelkov (2):
fs: stream_open - opener for stream-like files so that read and write can run simultaneously without deadlock
fuse: Add FOPEN_STREAM to use stream_open()
drivers/xen/xenbus/xenbus_dev_frontend.c | 2 +-
fs/fuse/file.c | 4 +-
fs/open.c | 18 ++
fs/read_write.c | 5 +-
include/linux/fs.h | 4 +
include/uapi/linux/fuse.h | 2 +
scripts/coccinelle/api/stream_open.cocci | 363 +++++++++++++++++++++++
7 files changed, 394 insertions(+), 4 deletions(-)
create mode 100644 scripts/coccinelle/api/stream_open.cocci
--
2.20.1
commit bbd84f33652f852ce5992d65db4d020aba21f882 upstream.
Starting from commit 9c225f2655e3 ("vfs: atomic f_pos accesses as per
POSIX") files opened even via nonseekable_open gate read and write via lock
and do not allow them to be run simultaneously. This can create read vs
write deadlock if a filesystem is trying to implement a socket-like file
which is intended to be simultaneously used for both read and write from
filesystem client. See commit 10dce8af3422 ("fs: stream_open - opener for
stream-like files so that read and write can run simultaneously without
deadlock") for details and e.g. commit 581d21a2d02a ("xenbus: fix deadlock
on writes to /proc/xen/xenbus") for a similar deadlock example on
/proc/xen/xenbus.
To avoid such deadlock it was tempting to adjust fuse_finish_open to use
stream_open instead of nonseekable_open on just FOPEN_NONSEEKABLE flags,
but grepping through Debian codesearch shows users of FOPEN_NONSEEKABLE,
and in particular GVFS which actually uses offset in its read and write
handlers
https://codesearch.debian.net/search?q=-%3Enonseekable+%3D
https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1080
https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1247-1346
https://gitlab.gnome.org/GNOME/gvfs/blob/1.40.0-6-gcbc54396/client/gvfsfusedaemon.c#L1399-1481
so if we would do such a change it will break a real user.
Add another flag (FOPEN_STREAM) for filesystem servers to indicate that the
opened handler is having stream-like semantics; does not use file position
and thus the kernel is free to issue simultaneous read and write request on
opened file handle.
This patch together with stream_open() should be added to stable kernels
starting from v3.14+. This will allow to patch OSSPD and other FUSE
filesystems that provide stream-like files to return FOPEN_STREAM |
FOPEN_NONSEEKABLE in open handler and this way avoid the deadlock on all
kernel versions. This should work because fuse_finish_open ignores unknown
open flags returned from a filesystem and so passing FOPEN_STREAM to a
kernel that is not aware of this flag cannot hurt. In turn the kernel that
is not aware of FOPEN_STREAM will be < v3.14 where just FOPEN_NONSEEKABLE
is sufficient to implement streams without read vs write deadlock.
Cc: [email protected] # v3.14+
Signed-off-by: Kirill Smelkov <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>
---
fs/fuse/file.c | 4 +++-
include/uapi/linux/fuse.h | 2 ++
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index d4dbea657656..b85a32be5c92 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -213,7 +213,9 @@ void fuse_finish_open(struct inode *inode, struct file *file)
file->f_op = &fuse_direct_io_file_operations;
if (!(ff->open_flags & FOPEN_KEEP_CACHE))
invalidate_inode_pages2(inode->i_mapping);
- if (ff->open_flags & FOPEN_NONSEEKABLE)
+ if (ff->open_flags & FOPEN_STREAM)
+ stream_open(inode, file);
+ else if (ff->open_flags & FOPEN_NONSEEKABLE)
nonseekable_open(inode, file);
if (fc->atomic_o_trunc && (file->f_flags & O_TRUNC)) {
struct fuse_inode *fi = get_fuse_inode(inode);
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 25084a052a1e..cff91b018953 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -205,10 +205,12 @@ struct fuse_file_lock {
* FOPEN_DIRECT_IO: bypass page cache for this open file
* FOPEN_KEEP_CACHE: don't invalidate the data cache on open
* FOPEN_NONSEEKABLE: the file is not seekable
+ * FOPEN_STREAM: the file is stream-like (no file position at all)
*/
#define FOPEN_DIRECT_IO (1 << 0)
#define FOPEN_KEEP_CACHE (1 << 1)
#define FOPEN_NONSEEKABLE (1 << 2)
+#define FOPEN_STREAM (1 << 4)
/**
* INIT request/reply flags
--
2.20.1