In the I/O locking code borrowed from NFS into netfslib, i_rwsem is held
locked across a buffered write - but this causes a performance regression
in cifs as it excludes buffered reads for the duration (cifs didn't use any
locking for buffered reads).

Mitigate this somewhat by downgrading the i_rwsem to a read lock across the
buffered write.  This at least allows parallel reads to occur whilst
excluding other writes, DIO, truncate and setattr.

Note that this shouldn't be a problem for a buffered write as a read
through an mmap can circumvent i_rwsem anyway.

Also note that we might want to make this change in NFS also.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/1317958.1729096113@warthog.procyon.org.uk
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Trond Myklebust <trondmy@kernel.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-cifs@vger.kernel.org
cc: linux-nfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

netfslib currently defers dropping the ref on the folios it obtains during
readahead to after it has started I/O on the basis that we can do it whilst
we wait for the I/O to complete, but this runs the risk of the I/O
collection racing with this in future.

Furthermore, Matthew Wilcox strongly suggests that the refs should be
dropped immediately, as readahead_folio() does (netfslib is using
__readahead_batch() which doesn't drop the refs).

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/3771538.1728052438@warthog.procyon.org.uk
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

After dividing up a proposed write into subrequests, netfslib sets
NETFS_RREQ_ALL_QUEUED to indicate to the collector that it can move on to
the final cleanup once it has emptied the subrequest queues.

Now, whilst the collector will normally end up running at least once after
this bit is set just because it takes a while to process all the write
subrequests before the collector runs out of subrequests, there exists the
possibility that the issuing thread will be forced to sleep and the
collector thread will clean up all the subrequests before ALL_QUEUED gets
set.

In such a case, the collector thread will not get triggered again and will
never clear NETFS_RREQ_IN_PROGRESS thus leaving a request uncompleted and
causing a potential futute hang.

Fix this by scheduling the write collector if all the subrequest queues are
empty (and thus no writes pending issuance).

Note that we'd do this ideally before queuing the subrequest, but in the
case of buffered writeback, at least, we can't find out that we've run out
of folios until after we've called writeback_iter() and it has returned
NULL - at which point we might not actually have any subrequests still
under construction.

Fixes: 288ace2f57c9 ("netfs: New writeback implementation")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/3317784.1727880350@warthog.procyon.org.uk
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Use folioq_count instead of folioq_nr_slots to fix a KMSAN uninit-value
error in netfs_clear_buffer

Signed-off-by: Chang Yu <marcus.yu.56@gmail.com>
Link: https://lore.kernel.org/r/ZvuXWC2bYpvQsWgS@gmail.com
Fixes: cd0277ed0c18 ("netfs: Use new folio_queue data type and iterator instead of xarray iter")
Acked-by: David Howells <dhowells@redhat.com>
Reported-by: syzbot+921873345a95f4dae7e9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=921873345a95f4dae7e9
Signed-off-by: Christian Brauner <brauner@kernel.org>

Pull vfs fixes from Christian Brauner:
 "afs:

   - Fix setting of the server responding flag

   - Remove unused struct afs_address_list and afs_put_address_list()
     function

   - Fix infinite loop because of unresponsive servers

   - Ensure that afs_retry_request() function is correctly added to the
     afs_req_ops netfs operations table

  netfs:

   - Fix netfs_folio tracepoint handling to handle NULL mappings

   - Add a missing folio_queue API documentation

   - Ensure that netfs_write_folio() correctly advances the iterator via
     iov_iter_advance()

   - Fix a dentry leak during concurrent cull and cookie lookup
     operations in cachefiles

  pidfs:

   - Correctly handle accessing another task's pid namespace"

* tag 'vfs-6.12-rc2.fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  netfs: Fix the netfs_folio tracepoint to handle NULL mapping
  netfs: Add folio_queue API documentation
  netfs: Advance iterator correctly rather than jumping it
  afs: Fix the setting of the server responding flag
  afs: Remove unused struct and function prototype
  afs: Fix possible infinite loop with unresponsive servers
  pidfs: check for valid pid namespace
  afs: Fix missing wire-up of afs_retry_request()
  cachefiles: fix dentry leak in cachefiles_open_file()

In netfs_write_folio(), use iov_iter_advance() to advance the folio as we
split bits of it off to subrequests rather than manually jumping the
->iov_offset value around.  This becomes more problematic when we use a
bounce buffer made out of single-page folios to cover a multipage pagecache
folio.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/2238548.1727424522@warthog.procyon.org.uk
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

In netfslib, a buffered writeback operation has a 'write queue' of folios
that are being written, held in a linear sequence of folio_queue structs.
The 'issuer' adds new folio_queues on the leading edge of the queue and
populates each one progressively; the 'collector' pops them off the
trailing edge and discards them and the folios they point to as they are
consumed.

The queue is required to always retain at least one folio_queue structure.
This allows the queue to be accessed without locking and with just a bit of
barriering.

When a new subrequest is prepared, its ->io_iter iterator is pointed at the
current end of the write queue and then the iterator is extended as more
data is added to the queue until the subrequest is committed.

Now, the problem is that the folio_queue at the leading edge of the write
queue when a subrequest is prepared might have been entirely consumed - but
not yet removed from the queue as it is the only remaining one and is
preventing the queue from collapsing.

So, what happens is that subreq->io_iter is pointed at the spent
folio_queue, then a new folio_queue is added, and, at that point, the
collector is at entirely at liberty to immediately delete the spent
folio_queue.

This leaves the subreq->io_iter pointing at a freed object.  If the system
is lucky, iterate_folioq() sees ->io_iter, sees the as-yet uncorrupted
freed object and advances to the next folio_queue in the queue.

In the case seen, however, the freed object gets recycled and put back onto
the queue at the tail and filled to the end.  This confuses
iterate_folioq() and it tries to step ->next, which may be NULL - resulting
in an oops.

Fix this by the following means:

 (1) When preparing a write subrequest, make sure there's a folio_queue
     struct with space in it at the leading edge of the queue.  A function
     to make space is split out of the function to append a folio so that
     it can be called for this purpose.

 (2) If the request struct iterator is pointing to a completely spent
     folio_queue when we make space, then advance the iterator to the newly
     allocated folio_queue.  The subrequest's iterator will then be set
     from this.

The oops could be triggered using the generic/346 xfstest with a filesystem
on9P over TCP with cache=loose.  The oops looked something like:

 BUG: kernel NULL pointer dereference, address: 0000000000000008
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 ...
 RIP: 0010:_copy_from_iter+0x2db/0x530
 ...
 Call Trace:
  <TASK>
 ...
  p9pdu_vwritef+0x3d8/0x5d0
  p9_client_prepare_req+0xa8/0x140
  p9_client_rpc+0x81/0x280
  p9_client_write+0xcf/0x1c0
  v9fs_issue_write+0x87/0xc0
  netfs_advance_write+0xa0/0xb0
  netfs_write_folio.isra.0+0x42d/0x500
  netfs_writepages+0x15a/0x1f0
  do_writepages+0xd1/0x220
  filemap_fdatawrite_wbc+0x5c/0x80
  v9fs_mmap_vm_close+0x7d/0xb0
  remove_vma+0x35/0x70
  vms_complete_munmap_vmas+0x11a/0x170
  do_vmi_align_munmap+0x17d/0x1c0
  do_vmi_munmap+0x13e/0x150
  __vm_munmap+0x92/0xd0
  __x64_sys_munmap+0x17/0x20
  do_syscall_64+0x80/0xe0
  entry_SYSCALL_64_after_hwframe+0x71/0x79

This also fixed a similar-looking issue with cifs and generic/074.

Fixes: cd0277ed0c18 ("netfs: Use new folio_queue data type and iterator instead of xarray iter")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202409180928.f20b5a08-oliver.sang@intel.com
Closes: https://lore.kernel.org/oe-lkp/202409131438.3f225fbf-oliver.sang@intel.com
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: kernel test robot <oliver.sang@intel.com>
cc: Eric Van Hensbergen <ericvh@kernel.org>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: v9fs@lists.linux.dev
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

The cifs flag CIFS_INO_MODIFIED_ATTR, which indicates that the mtime and
ctime need to be written back on close, got taken over by netfs as
NETFS_ICTX_MODIFIED_ATTR to avoid the need to call a function pointer to
set it.

The flag gets set correctly on buffered writes, but doesn't get set by
netfs_page_mkwrite(), leading to occasional failures in generic/080 and
generic/215.

Fix this by setting the flag in netfs_page_mkwrite().

Fixes: 73425800ac94 ("netfs, cifs: Move CIFS_INO_MODIFIED_ATTR to netfs_inode")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202409161629.98887b2-oliver.sang@intel.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

Pull netfs updates from Christian Brauner:
 "This contains the work to improve read/write performance for the new
  netfs library.

  The main performance enhancing changes are:

   - Define a structure, struct folio_queue, and a new iterator type,
     ITER_FOLIOQ, to hold a buffer as a replacement for ITER_XARRAY. See
     that patch for questions about naming and form.

     ITER_FOLIOQ is provided as a replacement for ITER_XARRAY. The
     problem with an xarray is that accessing it requires the use of a
     lock (typically the RCU read lock) - and this means that we can't
     supply iterate_and_advance() with a step function that might sleep
     (crypto for example) without having to drop the lock between pages.
     ITER_FOLIOQ is the iterator for a chain of folio_queue structs,
     where each folio_queue holds a small list of folios. A folio_queue
     struct is a simpler structure than xarray and is not subject to
     concurrent manipulation by the VM. folio_queue is used rather than
     a bvec[] as it can form lists of indefinite size, adding to one end
     and removing from the other on the fly.

   - Provide a copy_folio_from_iter() wrapper.

   - Make cifs RDMA support ITER_FOLIOQ.

   - Use folio queues in the write-side helpers instead of xarrays.

   - Add a function to reset the iterator in a subrequest.

   - Simplify the write-side helpers to use sheaves to skip gaps rather
     than trying to work out where gaps are.

   - In afs, make the read subrequests asynchronous, putting them into
     work items to allow the next patch to do progressive
     unlocking/reading.

   - Overhaul the read-side helpers to improve performance.

   - Fix the caching of a partial block at the end of a file.

   - Allow a store to be cancelled.

  Then some changes for cifs to make it use folio queues instead of
  xarrays for crypto bufferage:

   - Use raw iteration functions rather than manually coding iteration
     when hashing data.

   - Switch to using folio_queue for crypto buffers.

   - Remove the xarray bits.

  Make some adjustments to the /proc/fs/netfs/stats file such that:

   - All the netfs stats lines begin 'Netfs:' but change this to
     something a bit more useful.

   - Add a couple of stats counters to track the numbers of skips and
     waits on the per-inode writeback serialisation lock to make it
     easier to check for this as a source of performance loss.

  Miscellaneous work:

   - Ensure that the sb_writers lock is taken around
     vfs_{set,remove}xattr() in the cachefiles code.

   - Reduce the number of conditional branches in netfs_perform_write().

   - Move the CIFS_INO_MODIFIED_ATTR flag to the netfs_inode struct and
     remove cifs_post_modify().

   - Move the max_len/max_nr_segs members from netfs_io_subrequest to
     netfs_io_request as they're only needed for one subreq at a time.

   - Add an 'unknown' source value for tracing purposes.

   - Remove NETFS_COPY_TO_CACHE as it's no longer used.

   - Set the request work function up front at allocation time.

   - Use bh-disabling spinlocks for rreq->lock as cachefiles completion
     may be run from block-filesystem DIO completion in softirq context.

   - Remove fs/netfs/io.c"

* tag 'vfs-6.12.netfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (25 commits)
  docs: filesystems: corrected grammar of netfs page
  cifs: Don't support ITER_XARRAY
  cifs: Switch crypto buffer to use a folio_queue rather than an xarray
  cifs: Use iterate_and_advance*() routines directly for hashing
  netfs: Cancel dirty folios that have no storage destination
  cachefiles, netfs: Fix write to partial block at EOF
  netfs: Remove fs/netfs/io.c
  netfs: Speed up buffered reading
  afs: Make read subreqs async
  netfs: Simplify the writeback code
  netfs: Provide an iterator-reset function
  netfs: Use new folio_queue data type and iterator instead of xarray iter
  cifs: Provide the capability to extract from ITER_FOLIOQ to RDMA SGEs
  iov_iter: Provide copy_folio_from_iter()
  mm: Define struct folio_queue and ITER_FOLIOQ to handle a sequence of folios
  netfs: Use bh-disabling spinlocks for rreq->lock
  netfs: Set the request work function upon allocation
  netfs: Remove NETFS_COPY_TO_CACHE
  netfs: Reserve netfs_sreq_source 0 as unset/unknown
  netfs: Move max_len/max_nr_segs from netfs_io_subrequest to netfs_io_stream
  ...

Pull misc vfs updates from Christian Brauner:
 "This contains the usual pile of misc updates:

  Features:

   - Add F_CREATED_QUERY fcntl() that allows userspace to query whether
     a file was actually created. Often userspace wants to know whether
     an O_CREATE request did actually create a file without using
     O_EXCL. The current logic is that to first attempts to open the
     file without O_CREAT | O_EXCL and if ENOENT is returned userspace
     tries again with both flags. If that succeeds all is well. If it
     now reports EEXIST it retries.

     That works fairly well but some corner cases make this more
     involved. If this operates on a dangling symlink the first openat()
     without O_CREAT | O_EXCL will return ENOENT but the second openat()
     with O_CREAT | O_EXCL will fail with EEXIST.

     The reason is that openat() without O_CREAT | O_EXCL follows the
     symlink while O_CREAT | O_EXCL doesn't for security reasons. So
     it's not something we can really change unless we add an explicit
     opt-in via O_FOLLOW which seems really ugly.

     All available workarounds are really nasty (fanotify, bpf lsm etc)
     so add a simple fcntl().

   - Try an opportunistic lookup for O_CREAT. Today, when opening a file
     we'll typically do a fast lookup, but if O_CREAT is set, the kernel
     always takes the exclusive inode lock. This was likely done with
     the expectation that O_CREAT means that we always expect to do the
     create, but that's often not the case. Many programs set O_CREAT
     even in scenarios where the file already exists (see related
     F_CREATED_QUERY patch motivation above).

     The series contained in the pr rearranges the pathwalk-for-open
     code to also attempt a fast_lookup in certain O_CREAT cases. If a
     positive dentry is found, the inode_lock can be avoided altogether
     and it can stay in rcuwalk mode for the last step_into.

   - Expose the 64 bit mount id via name_to_handle_at()

     Now that we provide a unique 64-bit mount ID interface in statx(2),
     we can now provide a race-free way for name_to_handle_at(2) to
     provide a file handle and corresponding mount without needing to
     worry about racing with /proc/mountinfo parsing or having to open a
     file just to do statx(2).

     While this is not necessary if you are using AT_EMPTY_PATH and
     don't care about an extra statx(2) call, users that pass full paths
     into name_to_handle_at(2) need to know which mount the file handle
     comes from (to make sure they don't try to open_by_handle_at a file
     handle from a different filesystem) and switching to AT_EMPTY_PATH
     would require allocating a file for every name_to_handle_at(2) call

   - Add a per dentry expire timeout to autofs

     There are two fairly well known automounter map formats, the autofs
     format and the amd format (more or less System V and Berkley).

     Some time ago Linux autofs added an amd map format parser that
     implemented a fair amount of the amd functionality. This was done
     within the autofs infrastructure and some functionality wasn't
     implemented because it either didn't make sense or required extra
     kernel changes. The idea was to restrict changes to be within the
     existing autofs functionality as much as possible and leave changes
     with a wider scope to be considered later.

     One of these changes is implementing the amd options:
      1) "unmount", expire this mount according to a timeout (same as
         the current autofs default).
      2) "nounmount", don't expire this mount (same as setting the
         autofs timeout to 0 except only for this specific mount) .
      3) "utimeout=<seconds>", expire this mount using the specified
         timeout (again same as setting the autofs timeout but only for
         this mount)

     To implement these options per-dentry expire timeouts need to be
     implemented for autofs indirect mounts. This is because all map
     keys (mounts) for autofs indirect mounts use an expire timeout
     stored in the autofs mount super block info. structure and all
     indirect mounts use the same expire timeout.

  Fixes:

   - Fix missing fput for FSCONFIG_SET_FD in autofs

   - Use param->file for FSCONFIG_SET_FD in coda

   - Delete the 'fs/netfs' proc subtreee when netfs module exits

   - Make sure that struct uid_gid_map fits into a single cacheline

   - Don't flush in-flight wb switches for superblocks without cgroup
     writeback

   - Correcting the idmapping mount example in the idmapping
     documentation

   - Fix a race between evice_inodes() and find_inode() and iput()

   - Refine the show_inode_state() macro definition in writeback code

   - Prevent dump_mapping() from accessing invalid dentry.d_name.name

   - Show actual source for debugfs in /proc/mounts

   - Annotate data-race of busy_poll_usecs in eventpoll

   - Don't WARN for racy path_noexec check in exec code

   - Handle OOM on mnt_warn_timestamp_expiry()

   - Fix some spelling in the iomap design documentation

   - Fix typo in procfs comment

   - Fix typo in fs/namespace.c comment

  Cleanups:

   - Add the VFS git tree to the MAINTAINERS file

   - Move FMODE_UNSIGNED_OFFSET to fop_flags freeing up another f_mode
     bit in struct file bringing us to 5 free f_mode bits

   - Remove the __I_DIO_WAKEUP bit from i_state flags as we can simplify
     the wait mechanism

   - Remove the unused path_put_init() helper

   - Replace a __u32 with u32 for s_fsnotify_mask as __u32 is uapi
     specific

   - Replace the unsigned long i_state member with a u32 i_state member
     in struct inode freeing up 4 bytes in struct inode. Instead of
     using the bit based wait apis we're now using the var event apis
     and using the individual bytes of the i_state member to wait on
     state changes

   - Explain how per-syscall AT_* flags should be allocated

   - Use in_group_or_capable() helper to simplify the posix acl mode
     update code

   - Switch to LIST_HEAD() in fsync_buffers_list() to simplify the code

   - Removed comment about d_rcu_to_refcount() as that function doesn't
     exist anymore

   - Add kernel documentation for lookup_fast()

   - Don't re-zero evenpoll fields

   - Remove outdated comment after close_fd()

   - Fix imprecise wording in comment about the pipe filesystem

   - Drop GFP_NOFAIL mode from alloc_page_buffers

   - Missing blank line warnings and struct declaration improved in
     file_table

   - Annotate struct poll_list with __counted_by()

   - Remove the unused read parameter in percpu-rwsem

   - Remove linux/prefetch.h include from direct-io code

   - Use kmemdup_array instead of kmemdup for multiple allocation in
     mnt_idmapping code

   - Remove unused mnt_cursor_del() declaration

  Performance tweaks:

   - Dodge smp_mb in break_lease and break_deleg in the common case

   - Only read fops once in fops_{get,put}()

   - Use RCU in ilookup()

   - Elide smp_mb in iversion handling in the common case

   - Drop one lock trip in evict()"

* tag 'vfs-6.12.misc' of gitolite.kernel.org:pub/scm/linux/kernel/git/vfs/vfs: (58 commits)
  uidgid: make sure we fit into one cacheline
  proc: Fix typo in the comment
  fs/pipe: Correct imprecise wording in comment
  fhandle: expose u64 mount id to name_to_handle_at(2)
  uapi: explain how per-syscall AT_* flags should be allocated
  fs: drop GFP_NOFAIL mode from alloc_page_buffers
  writeback: Refine the show_inode_state() macro definition
  fs/inode: Prevent dump_mapping() accessing invalid dentry.d_name.name
  mnt_idmapping: Use kmemdup_array instead of kmemdup for multiple allocation
  netfs: Delete subtree of 'fs/netfs' when netfs module exits
  fs: use LIST_HEAD() to simplify code
  inode: make i_state a u32
  inode: port __I_LRU_ISOLATING to var event
  vfs: fix race between evice_inodes() and find_inode()&iput()
  inode: port __I_NEW to var event
  inode: port __I_SYNC to var event
  fs: reorder i_state bits
  fs: add i_state helpers
  MAINTAINERS: add the VFS git tree
  fs: s/__u32/u32/ for s_fsnotify_mask
  ...