[PATCH 4.4 0/2] Fix FUSE read/write deadlock on stream-like files

[Kirill Smelkov]

Hello stable team,

Please consider applying the following 2 patches to Linux-4.4 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:
stable@xxxxxxxxxxxxxxx # 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 4.4 (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@xxxxxxxxxxxxxx/
https://lore.kernel.org/linux-fsdevel/20190424183012.GB3798@xxxxxxxxxxxxxxxxxxx/
https://lore.kernel.org/linux-fsdevel/20190424191652.GE3798@xxxxxxxxxxxxxxxxxxx/
...

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

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2.20.1