[PATCH 0/3] FUSE passthrough fixes

[Amir Goldstein <amir73il@gmail.com>]

Miklos,

While going over the code to prepare for getattr() passthrough I
experienced a WTF moment that resulted in the two fix patches.

Patch 3/3 is included for reference and to give Sweet Tea a starting
point for getattr() passthrough.

What puzzled me is that some ff->iomode state bugs were so blunt that
I needed to figure out how I did not see any WARN_ON in my tests of rc1.
There are different reasons for different types of bugs.

1. For concurrent dio writes without any passthrough open,
fuse_file_cached_io_start() was supposed to hit
WARN_ON(ff->iomode == IOM_UNCACHED) if there is already a dio write
in-flight.

My conclusion is that the set of fstests that run on passthrough_hp,
on my small test VM do not excercise concurrent dio writes.

2. For dio write, where the file was opened passthrough, every write
was going to hit WARN_ON(ff->iomode == IOM_UNCACHED) and also
fuse_file_cached_io_end() was going to set ff->iomode == IOM_NONE
and leak the fuse_backing object.

However, the bug fixed by patch 2/3 made sure that parallel dio write
would always fallback to exclusive dio if file was open with a backing
file.

Testing:

I ran fstests with passthrough_hp with options:
1) FOPEN_PASSTHROUGH
2) FOPEN_DIRECT_IO | FOPEN_PARALLEL_DIRECT_WRITES
3) FOPEN_PASSTHROUGH | FOPEN_DIRECT_IO | FOPEN_PARALLEL_DIRECT_WRITES

Did not observe any regressions (not any improvments) from rc1.

Ran some multi threads aiodio tests with just patch 2/3 and the
assertions in fuse_evict_inode() from patch 3/3.

First two configs did not hit any assertion.
The passthrough+direct_io+parallel_direct_writes config always
hits the assertion in fuse_file_cached_io_start() and always hits
the leaked fuse_backing assertion in fuse_evict_inode().

Bernd do you have different tests to cover concurrent dio writes in
your setup? Any ideas on how to improve the fstests test coverage?

Thanks,
Amir.

Amir Goldstein (3):
  fuse: fix wrong ff->iomode state changes from parallel dio write
  fuse: fix parallel dio write on file open in passthrough mode
  fuse: prepare for long lived reference on backing file

 fs/fuse/file.c   | 18 +++++++-----
 fs/fuse/fuse_i.h | 10 +++++--
 fs/fuse/inode.c  |  7 +++++
 fs/fuse/iomode.c | 73 +++++++++++++++++++++++++++++++++---------------
 4 files changed, 76 insertions(+), 32 deletions(-)

-- 
2.34.1