Pull block updates from Jens Axboe:

 - NVMe updates via Keith:
     - Device initialization memory leak fixes (Keith)
     - More constants defined (Weiwen)
     - Target debugfs support (Hannes)
     - PCIe subsystem reset enhancements (Keith)
     - Queue-depth multipath policy (Redhat and PureStorage)
     - Implement get_unique_id (Christoph)
     - Authentication error fixes (Gaosheng)

 - MD updates via Song
     - sync_action fix and refactoring (Yu Kuai)
     - Various small fixes (Christoph Hellwig, Li Nan, and Ofir Gal, Yu
       Kuai, Benjamin Marzinski, Christophe JAILLET, Yang Li)

 - Fix loop detach/open race (Gulam)

 - Fix lower control limit for blk-throttle (Yu)

 - Add module descriptions to various drivers (Jeff)

 - Add support for atomic writes for block devices, and statx reporting
   for same. Includes SCSI and NVMe (John, Prasad, Alan)

 - Add IO priority information to block trace points (Dongliang)

 - Various zone improvements and tweaks (Damien)

 - mq-deadline tag reservation improvements (Bart)

 - Ignore direct reclaim swap writes in writeback throttling (Baokun)

 - Block integrity improvements and fixes (Anuj)

 - Add basic support for rust based block drivers. Has a dummy null_blk
   variant for now (Andreas)

 - Series converting driver settings to queue limits, and cleanups and
   fixes related to that (Christoph)

 - Cleanup for poking too deeply into the bvec internals, in preparation
   for DMA mapping API changes (Christoph)

 - Various minor tweaks and fixes (Jiapeng, John, Kanchan, Mikulas,
   Ming, Zhu, Damien, Christophe, Chaitanya)

* tag 'for-6.11/block-20240710' of git://git.kernel.dk/linux: (206 commits)
  floppy: add missing MODULE_DESCRIPTION() macro
  loop: add missing MODULE_DESCRIPTION() macro
  ublk_drv: add missing MODULE_DESCRIPTION() macro
  xen/blkback: add missing MODULE_DESCRIPTION() macro
  block/rnbd: Constify struct kobj_type
  block: take offset into account in blk_bvec_map_sg again
  block: fix get_max_segment_size() warning
  loop: Don't bother validating blocksize
  virtio_blk: Don't bother validating blocksize
  null_blk: Don't bother validating blocksize
  block: Validate logical block size in blk_validate_limits()
  virtio_blk: Fix default logical block size fallback
  nvmet-auth: fix nvmet_auth hash error handling
  nvme: implement ->get_unique_id
  block: pass a phys_addr_t to get_max_segment_size
  block: add a bvec_phys helper
  blk-lib: check for kill signal in ioctl BLKZEROOUT
  block: limit the Write Zeroes to manually writing zeroes fallback
  block: refacto blkdev_issue_zeroout
  block: move read-only and supported checks into (__)blkdev_issue_zeroout
  ...

Pull vfs inode / dentry updates from Christian Brauner:
 "This contains smaller performance improvements to inodes and dentries:

  inode:

   - Add rcu based inode lookup variants.

     They avoid one inode hash lock acquire in the common case thereby
     significantly reducing contention. We already support RCU-based
     operations but didn't take advantage of them during inode
     insertion.

     Callers of iget_locked() get the improvement without any code
     changes. Callers that need a custom callback can switch to
     iget5_locked_rcu() as e.g., did btrfs.

     With 20 threads each walking a dedicated 1000 dirs * 1000 files
     directory tree to stat(2) on a 32 core + 24GB ram vm:

        before: 3.54s user 892.30s system 1966% cpu 45.549 total
        after:  3.28s user 738.66s system 1955% cpu 37.932 total (-16.7%)

     Long-term we should pick up the effort to introduce more
     fine-grained locking and possibly improve on the currently used
     hash implementation.

   - Start zeroing i_state in inode_init_always() instead of doing it in
     individual filesystems.

     This allows us to remove an unneeded lock acquire in new_inode()
     and not burden individual filesystems with this.

  dcache:

   - Move d_lockref out of the area used by RCU lookup to avoid
     cacheline ping poing because the embedded name is sharing a
     cacheline with d_lockref.

   - Fix dentry size on 32bit with CONFIG_SMP=y so it does actually end
     up with 128 bytes in total"

* tag 'vfs-6.11.inode' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  fs: fix dentry size
  vfs: move d_lockref out of the area used by RCU lookup
  bcachefs: remove now spurious i_state initialization
  xfs: remove now spurious i_state initialization in xfs_inode_alloc
  vfs: partially sanitize i_state zeroing on inode creation
  xfs: preserve i_state around inode_init_always in xfs_reinit_inode
  btrfs: use iget5_locked_rcu
  vfs: add rcu-based find_inode variants for iget ops

Pull vfs casefolding updates from Christian Brauner:
 "This contains some work to simplify the handling of casefolded names:

   - Simplify the handling of casefolded names in f2fs and ext4 by
     keeping the names as a qstr to avoiding unnecessary conversions

   - Introduce a new generic_ci_match() libfs case-insensitive lookup
     helper and use it in both f2fs and ext4 allowing to remove the
     filesystem specific implementations

   - Remove a bunch of ifdefs by making the unicode build checks part of
     the code flow"

* tag 'vfs-6.11.casefold' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  f2fs: Move CONFIG_UNICODE defguards into the code flow
  ext4: Move CONFIG_UNICODE defguards into the code flow
  f2fs: Reuse generic_ci_match for ci comparisons
  ext4: Reuse generic_ci_match for ci comparisons
  libfs: Introduce case-insensitive string comparison helper
  f2fs: Simplify the handling of cached casefolded names
  ext4: Simplify the handling of cached casefolded names

The routine is used by procfs through dir_emit_dots.

The combined RCU and lock fallback implementation is too big for an
inline. Given that the routine takes a dentry argument fs/dcache.c seems
like the place to put it in.

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240627161152.802567-1-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Make it possible to quickly check whether AT_EMPTY_PATH is valid.
Note, after some discussion we decided to also allow NULL to be passed
instead of requiring the empty string.

Signed-off-by: Christian Brauner <brauner@kernel.org>

Export in_group_or_capable() as a VFS helper function.

Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Link: https://lore.kernel.org/r/20240620032335.147136-1-youling.tang@linux.dev
Signed-off-by: Christian Brauner <brauner@kernel.org>

Extend statx system call to return additional info for atomic write support
support for a file.

Helper function generic_fill_statx_atomic_writes() can be used by FSes to
fill in the relevant statx fields. For now atomic_write_segments_max will
always be 1, otherwise some rules would need to be imposed on iovec length
and alignment, which we don't want now.

Signed-off-by: Prasad Singamsetty <prasad.singamsetty@oracle.com>
jpg: relocate bdev support to another patch
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20240620125359.2684798-5-john.g.garry@oracle.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

An atomic write is a write issued with torn-write protection, meaning
that for a power failure or any other hardware failure, all or none of the
data from the write will be stored, but never a mix of old and new data.

Userspace may add flag RWF_ATOMIC to pwritev2() to indicate that the
write is to be issued with torn-write prevention, according to special
alignment and length rules.

For any syscall interface utilizing struct iocb, add IOCB_ATOMIC for
iocb->ki_flags field to indicate the same.

A call to statx will give the relevant atomic write info for a file:
- atomic_write_unit_min
- atomic_write_unit_max
- atomic_write_segments_max

Both min and max values must be a power-of-2.

Applications can avail of atomic write feature by ensuring that the total
length of a write is a power-of-2 in size and also sized between
atomic_write_unit_min and atomic_write_unit_max, inclusive. Applications
must ensure that the write is at a naturally-aligned offset in the file
wrt the total write length. The value in atomic_write_segments_max
indicates the upper limit for IOV_ITER iovcnt.

Add file mode flag FMODE_CAN_ATOMIC_WRITE, so files which do not have the
flag set will have RWF_ATOMIC rejected and not just ignored.

Add a type argument to kiocb_set_rw_flags() to allows reads which have
RWF_ATOMIC set to be rejected.

Helper function generic_atomic_write_valid() can be used by FSes to verify
compliant writes. There we check for iov_iter type is for ubuf, which
implies iovcnt==1 for pwritev2(), which is an initial restriction for
atomic_write_segments_max. Initially the only user will be bdev file
operations write handler. We will rely on the block BIO submission path to
ensure write sizes are compliant for the bdev, so we don't need to check
atomic writes sizes yet.

Signed-off-by: Prasad Singamsetty <prasad.singamsetty@oracle.com>
jpg: merge into single patch and much rewrite
Acked-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20240620125359.2684798-4-john.g.garry@oracle.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

This avoids one inode hash lock acquire in the common case on inode
creation, in effect significantly reducing contention.

On the stock kernel said lock is typically taken twice:
1. once to check if the inode happens to already be present
2. once to add it to the hash

The back-to-back lock/unlock pattern is known to degrade performance
significantly, which is further exacerbated if the hash is heavily
populated (long chains to walk, extending hold time). Arguably hash
sizing and hashing algo need to be revisited, but that's beyond the
scope of this patch.

With the acquire from step 1 eliminated with RCU lookup throughput
increases significantly at the scale of 20 cores (benchmark results at
the bottom).

So happens the hash already supports RCU-based operation, but lookups on
inode insertions didn't take advantage of it.

This of course has its limits as the global lock is still a bottleneck.
There was a patchset posted which introduced fine-grained locking[1] but
it appears staled. Apart from that doubt was expressed whether a
handrolled hash implementation is appropriate to begin with, suggesting
replacement with rhashtables. Nobody committed to carrying [1] across
the finish line or implementing anything better, thus the bandaid below.

iget_locked consumers (notably ext4) get away without any changes
because inode comparison method is built-in.

iget5_locked consumers pass a custom callback. Since removal of locking
adds more problems (inode can be changing) it's not safe to assume all
filesystems happen to cope.  Thus iget5_locked_rcu gets added, requiring
manual conversion of interested filesystems.

In order to reduce code duplication find_inode and find_inode_fast grow
an argument indicating whether inode hash lock is held, which is passed
down in case sleeping is necessary. They always rcu_read_lock, which is
redundant but harmless. Doing it conditionally reduces readability for
no real gain that I can see. RCU-alike restrictions were already put on
callbacks due to the hash spinlock being held.

Benchmarking:
There is a real cache-busting workload scanning millions of files in
parallel (it's a backup appliance), where the initial lookup is
guaranteed to fail resulting in the two lock acquires on stock kernel
(and one with the patch at hand).

Implemented below is a synthetic benchmark providing the same behavior.
[I shall note the workload is not running on Linux, instead it was
causing trouble elsewhere. Benchmark below was used while addressing
said problems and was found to adequately represent the real workload.]

Total real time fluctuates by 1-2s.

With 20 threads each walking a dedicated 1000 dirs * 1000 files
directory tree to stat(2) on a 32 core + 24GB RAM vm:

ext4 (needed mkfs.ext4 -N 24000000):
before: 3.77s user 890.90s system 1939% cpu 46.118 total
after:  3.24s user 397.73s system 1858% cpu 21.581 total (-53%)

That's 20 million files to visit, while the machine can only cache about
15 million at a time (obtained from ext4_inode_cache object count in
/proc/slabinfo). Since each terminal inode is only visited once per run
this amounts to 0% hit ratio for the dentry cache and the hash table
(there are however hits for the intermediate directories).

On repeated runs the kernel caches the last ~15 mln, meaning there is ~5
mln of uncached inodes which are going to be visited first, evicting the
previously cached state as it happens.

Lack of hits can be trivially verified with bpftrace, like so:
bpftrace -e 'kretprobe:find_inode_fast { @[kstack(), retval != 0] = count(); }'\
-c "/bin/sh walktrees /testfs 20"

Best ran more than once.

Expected results after "warmup":
[snip]
@[
    __ext4_iget+275
    ext4_lookup+224
    __lookup_slow+130
    walk_component+219
    link_path_walk.part.0.constprop.0+614
    path_lookupat+62
    filename_lookup+204
    vfs_statx+128
    vfs_fstatat+131
    __do_sys_newfstatat+38
    do_syscall_64+87
    entry_SYSCALL_64_after_hwframe+118
, 1]: 20000
@[
    __ext4_iget+275
    ext4_lookup+224
    __lookup_slow+130
    walk_component+219
    path_lookupat+106
    filename_lookup+204
    vfs_statx+128
    vfs_fstatat+131
    __do_sys_newfstatat+38
    do_syscall_64+87
    entry_SYSCALL_64_after_hwframe+118
, 1]: 20000000

That is 20 million calls for the initial lookup and 20 million after
allocating a new inode, all of them failing to return a value != 0
(i.e., they are returning NULL -- no match found).

Of course aborting the benchmark in the middle and starting it again (or
messing with the state in other ways) is going to alter these results.

Benchmark can be found here: https://people.freebsd.org/~mjg/fstree.tgz

[1] https://lore.kernel.org/all/20231206060629.2827226-1-david@fromorbit.com/

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20240611173824.535995-2-mjguzik@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

generic_ci_match can be used by case-insensitive filesystems to compare
strings under lookup with dirents in a case-insensitive way.  This
function is currently reimplemented by each filesystem supporting
casefolding, so this reduces code duplication in filesystem-specific
code.

[eugen.hristev@collabora.com: rework to first test the exact match, cleanup
and add error message]

Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
Link: https://lore.kernel.org/r/20240606073353.47130-4-eugen.hristev@collabora.com
Reviewed-by: Gabriel Krisman Bertazi <krisman@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>