Pull io_uring iov_iter retry fixes from Jens Axboe:
 "This adds a helper to save/restore iov_iter state, and modifies
  io_uring to use it.

  After that is done, we can now kill the iter->truncated addition that
  we added for this release. The io_uring change is being overly
  cautious with the save/restore/advance, but better safe than sorry and
  we can always improve that and reduce the overhead if it proves to be
  of concern. The only case to be worried about in this regard is huge
  IO, where iteration can take a while to iterate segments.

  I spent some time writing test cases, and expanded the coverage quite
  a bit from the last posting of this. liburing carries this regression
  test case now:

      https://git.kernel.dk/cgit/liburing/tree/test/file-verify.c

  which exercises all of this. It now also supports provided buffers,
  and explicitly tests for end-of-file/device truncation as well.

  On top of that, Pavel sanitized the IOPOLL retry path to follow the
  exact same pattern as normal IO"

* tag 'iov_iter.3-5.15-2021-09-17' of git://git.kernel.dk/linux-block:
  io_uring: move iopoll reissue into regular IO path
  Revert "iov_iter: track truncated size"
  io_uring: use iov_iter state save/restore helpers
  iov_iter: add helper to save iov_iter state

Pull io_uring fixes from Jens Axboe:
 "Mostly fixes for regressions in this cycle, but also a few fixes that
  predate this release.

  The odd one out is a tweak to the direct files added in this release,
  where attempting to reuse a slot is allowed instead of needing an
  explicit removal of that slot first. It's a considerable improvement
  in usability to that API, hence I'm sending it for -rc2.

   - io-wq race fix and cleanup (Hao)

   - loop_rw_iter() type fix

   - SQPOLL max worker race fix

   - Allow poll arm for O_NONBLOCK files, fixing a case where it's
     impossible to properly use io_uring if you cannot modify the file
     flags

   - Allow direct open to simply reuse a slot, instead of needing it
     explicitly removed first (Pavel)

   - Fix a case where we missed signal mask restoring in cqring_wait, if
     we hit -EFAULT (Xiaoguang)"

* tag 'io_uring-5.15-2021-09-17' of git://git.kernel.dk/linux-block:
  io_uring: allow retry for O_NONBLOCK if async is supported
  io_uring: auto-removal for direct open/accept
  io_uring: fix missing sigmask restore in io_cqring_wait()
  io_uring: pin SQPOLL data before unlocking ring lock
  io-wq: provide IO_WQ_* constants for IORING_REGISTER_IOWQ_MAX_WORKERS arg items
  io-wq: fix potential race of acct->nr_workers
  io-wq: code clean of io_wqe_create_worker()
  io_uring: ensure symmetry in handling iter types in loop_rw_iter()

The qnx4 directory entries are 64-byte blocks that have different
contents depending on the a status byte that is in the last byte of the
block.

In particular, a directory entry can be either a "link info" entry with
a 48-byte name and pointers to the real inode information, or an "inode
entry" with a smaller 16-byte name and the full inode information.

But the code was written to always just treat the directory name as if
it was part of that "inode entry", and just extend the name to the
longer case if the status byte said it was a link entry.

That work just fine and gives the right results, but now that gcc is
tracking data structure accesses much more, the code can trigger a
compiler error about using up to 48 bytes (the long name) in a structure
that only has that shorter name in it:

   fs/qnx4/dir.c: In function ‘qnx4_readdir’:
   fs/qnx4/dir.c:51:32: error: ‘strnlen’ specified bound 48 exceeds source size 16 [-Werror=stringop-overread]
      51 |                         size = strnlen(de->di_fname, size);
         |                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~
   In file included from fs/qnx4/qnx4.h:3,
                    from fs/qnx4/dir.c:16:
   include/uapi/linux/qnx4_fs.h:45:25: note: source object declared here
      45 |         char            di_fname[QNX4_SHORT_NAME_MAX];
         |                         ^~~~~~~~

which is because the source code doesn't really make this whole "one of
two different types" explicit.

Fix this by introducing a very explicit union of the two types, and
basically explaining to the compiler what is really going on.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

230d50d448acb ("io_uring: move reissue into regular IO path")
made non-IOPOLL I/O to not retry from ki_complete handler. Follow it
steps and do the same for IOPOLL. Same problems, same implementation,
same -EAGAIN assumptions.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f80dfee2d5fa7678f0052a8ab3cfca9496a112ca.1631699928.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Get rid of the need to do re-expand and revert on an iterator when we
encounter a short IO, or failure that warrants a retry. Use the new
state save/restore helpers instead.

We keep the iov_iter_state persistent across retries, if we need to
restart the read or write operation. If there's a pending retry, the
operation will always exit with the state correctly saved.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

A common complaint is that using O_NONBLOCK files with io_uring can be a
bit of a pain. Be a bit nicer and allow normal retry IFF the file does
support async behavior. This makes it possible to use io_uring more
reliably with O_NONBLOCK files, for use cases where it either isn't
possible or feasible to modify the file flags.

Cc: stable@vger.kernel.org
Reported-and-tested-by: Dan Melnic <dmm@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

It might be inconvenient that direct open/accept deviates from the
update semantics and fails if the slot is taken instead of removing a
file sitting there. Implement this auto-removal.

Note that removal might need to allocate and so may fail. However, if an
empty slot is specified, it's guaraneed to not fail on the fd
installation side for valid userspace programs. It's needed for users
who can't tolerate such failures, e.g. accept where the other end
never retries.

Suggested-by: Franz-B. Tuneke <franz-bernhard.tuneke@tu-dortmund.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/c896f14ea46b0eaa6c09d93149e665c2c37979b4.1631632300.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Move get_timespec() section in io_cqring_wait() before the sigmask
saving, otherwise we'll fail to restore sigmask once get_timespec()
returns error.

Fixes: c73ebb685fb6 ("io_uring: add timeout support for io_uring_enter()")
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Link: https://lore.kernel.org/r/20210914143852.9663-1-xiaoguang.wang@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We need to re-check sqd->thread after we've dropped the lock. Pin
the sqd before doing the lockdep lock dance, and check if the thread
is alive after that. It's either NULL or alive, as the SQPOLL thread
cannot exit without holding the same sqd->lock.

Reported-and-tested-by: syzbot+337de45f13a4fd54d708@syzkaller.appspotmail.com
Fixes: fa84693b3c89 ("io_uring: ensure IORING_REGISTER_IOWQ_MAX_WORKERS works with SQPOLL")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

The items passed in the array pointed by the arg parameter
of IORING_REGISTER_IOWQ_MAX_WORKERS io_uring_register operation
carry certain semantics: they refer to different io-wq worker categories;
provide IO_WQ_* constants in the UAPI, so these categories can be referenced
in the user space code.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Complements: 2e480058ddc21ec5 ("io-wq: provide a way to limit max number of workers")
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Link: https://lore.kernel.org/r/20210913154415.GA12890@asgard.redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>