Merge tag 'apparmor-pr-2022-08-08' of git://git.kernel.org/pub/scm/linux/kernel/git/jj/linux-apparmor

Pull AppArmor updates from John Johansen:
 "This is mostly cleanups and bug fixes with the one bigger change being
  Mathew Wilcox's patch to use XArrays instead of the IDR from the
  thread around the locking weirdness.

  Features:
   - Convert secid mapping to XArrays instead of IDR
   - Add a kernel label to use on kernel objects
   - Extend policydb permission set by making use of the xbits
   - Make export of raw binary profile to userspace optional
   - Enable tuning of policy paranoid load for embedded systems
   - Don't create raw_sha1 symlink if sha1 hashing is disabled
   - Allow labels to carry debug flags

  Cleanups:
   - Update MAINTAINERS file
   - Use struct_size() helper in kmalloc()
   - Move ptrace mediation to more logical task.{h,c}
   - Resolve uninitialized symbol warnings
   - Remove redundant ret variable
   - Mark alloc_unconfined() as static
   - Update help description of policy hash for introspection
   - Remove some casts which are no-longer required

  Bug Fixes:
   - Fix aa_label_asxprint return check
   - Fix reference count leak in aa_pivotroot()
   - Fix memleak in aa_simple_write_to_buffer()
   - Fix kernel doc comments
   - Fix absroot causing audited secids to begin with =
   - Fix quiet_denied for file rules
   - Fix failed mount permission check error message
   - Disable showing the mode as part of a secid to secctx
   - Fix setting unconfined mode on a loaded profile
   - Fix overlapping attachment computation
   - Fix undefined reference to `zlib_deflate_workspacesize'"

* tag 'apparmor-pr-2022-08-08' of git://git.kernel.org/pub/scm/linux/kernel/git/jj/linux-apparmor: (34 commits)
  apparmor: Update MAINTAINERS file with new email address
  apparmor: correct config reference to intended one
  apparmor: move ptrace mediation to more logical task.{h,c}
  apparmor: extend policydb permission set by making use of the xbits
  apparmor: allow label to carry debug flags
  apparmor: fix overlapping attachment computation
  apparmor: fix setting unconfined mode on a loaded profile
  apparmor: Fix some kernel-doc comments
  apparmor: Mark alloc_unconfined() as static
  apparmor: disable showing the mode as part of a secid to secctx
  apparmor: Convert secid mapping to XArrays instead of IDR
  apparmor: add a kernel label to use on kernel objects
  apparmor: test: Remove some casts which are no-longer required
  apparmor: Fix memleak in aa_simple_write_to_buffer()
  apparmor: fix reference count leak in aa_pivotroot()
  apparmor: Fix some kernel-doc comments
  apparmor: Fix undefined reference to `zlib_deflate_workspacesize'
  apparmor: fix aa_label_asxprint return check
  apparmor: Fix some kernel-doc comments
  apparmor: Fix some kernel-doc comments
  ...

Pull Kbuild updates from Masahiro Yamada:

 - Remove the support for -O3 (CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3)

 - Fix error of rpm-pkg cross-builds

 - Support riscv for checkstack tool

 - Re-enable -Wformwat warnings for Clang

 - Clean up modpost, Makefiles, and misc scripts

* tag 'kbuild-v5.20' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild: (30 commits)
  modpost: remove .symbol_white_list field entirely
  modpost: remove unneeded .symbol_white_list initializers
  modpost: add PATTERNS() helper macro
  modpost: shorten warning messages in report_sec_mismatch()
  Revert "Kbuild, lto, workaround: Don't warn for initcall_reference in modpost"
  modpost: use more reliable way to get fromsec in section_rel(a)()
  modpost: add array range check to sec_name()
  modpost: refactor get_secindex()
  kbuild: set EXIT trap before creating temporary directory
  modpost: remove unused Elf_Sword macro
  Makefile.extrawarn: re-enable -Wformat for clang
  kbuild: add dtbs_prepare target
  kconfig: Qt5: tell the user which packages are required
  modpost: use sym_get_data() to get module device_table data
  modpost: drop executable ELF support
  checkstack: add riscv support for scripts/checkstack.pl
  kconfig: shorten the temporary directory name for cc-option
  scripts: headers_install.sh: Update config leak ignore entries
  kbuild: error out if $(INSTALL_MOD_PATH) contains % or :
  kbuild: error out if $(KBUILD_EXTMOD) contains % or :
  ...

Let's have a look at this piece of code in __bread_slow:

	get_bh(bh);
	bh->b_end_io = end_buffer_read_sync;
	submit_bh(REQ_OP_READ, 0, bh);
	wait_on_buffer(bh);
	if (buffer_uptodate(bh))
		return bh;

Neither wait_on_buffer nor buffer_uptodate contain any memory barrier.
Consequently, if someone calls sb_bread and then reads the buffer data,
the read of buffer data may be executed before wait_on_buffer(bh) on
architectures with weak memory ordering and it may return invalid data.

Fix this bug by adding a memory barrier to set_buffer_uptodate and an
acquire barrier to buffer_uptodate (in a similar way as
folio_test_uptodate and folio_mark_uptodate).
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull nfsd updates from Chuck Lever:
 "Work on 'courteous server', which was introduced in 5.19, continues
  apace. This release introduces a more flexible limit on the number of
  NFSv4 clients that NFSD allows, now that NFSv4 clients can remain in
  courtesy state long after the lease expiration timeout. The client
  limit is adjusted based on the physical memory size of the server.

  The NFSD filecache is a cache of files held open by NFSv4 clients or
  recently touched by NFSv2 or NFSv3 clients. This cache had some
  significant scalability constraints that have been relieved in this
  release. Thanks to all who contributed to this work.

  A data corruption bug found during the most recent NFS bake-a-thon
  that involves NFSv3 and NFSv4 clients writing the same file has been
  addressed in this release.

  This release includes several improvements in CPU scalability for
  NFSv4 operations. In addition, Neil Brown provided patches that
  simplify locking during file lookup, creation, rename, and removal
  that enables subsequent work on making these operations more scalable.
  We expect to see that work materialize in the next release.

  There are also numerous single-patch fixes, clean-ups, and the usual
  improvements in observability"

* tag 'nfsd-6.0' of git://git.kernel.org/pub/scm/linux/kernel/git/cel/linux: (78 commits)
  lockd: detect and reject lock arguments that overflow
  NFSD: discard fh_locked flag and fh_lock/fh_unlock
  NFSD: use (un)lock_inode instead of fh_(un)lock for file operations
  NFSD: use explicit lock/unlock for directory ops
  NFSD: reduce locking in nfsd_lookup()
  NFSD: only call fh_unlock() once in nfsd_link()
  NFSD: always drop directory lock in nfsd_unlink()
  NFSD: change nfsd_create()/nfsd_symlink() to unlock directory before returning.
  NFSD: add posix ACLs to struct nfsd_attrs
  NFSD: add security label to struct nfsd_attrs
  NFSD: set attributes when creating symlinks
  NFSD: introduce struct nfsd_attrs
  NFSD: verify the opened dentry after setting a delegation
  NFSD: drop fh argument from alloc_init_deleg
  NFSD: Move copy offload callback arguments into a separate structure
  NFSD: Add nfsd4_send_cb_offload()
  NFSD: Remove kmalloc from nfsd4_do_async_copy()
  NFSD: Refactor nfsd4_do_copy()
  NFSD: Refactor nfsd4_cleanup_inter_ssc() (2/2)
  NFSD: Refactor nfsd4_cleanup_inter_ssc() (1/2)
  ...

Merge tag 'fscache-fixes-20220809' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull fscache updates from David Howells:

 - Fix a cookie access ref leak if a cookie is invalidated a second time
   before the first invalidation is actually processed.

 - Add a tracepoint to log cookie lookup failure

* tag 'fscache-fixes-20220809' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  fscache: add tracepoint when failing cookie
  fscache: don't leak cookie access refs if invalidation is in progress or failed

Pull AFS fixes from David Howells:
 "Fix AFS refcount handling.

  The first patch converts afs to use refcount_t for its refcounts and
  the second patch fixes afs_put_call() and afs_put_server() to save the
  values they're going to log in the tracepoint before decrementing the
  refcount"

* tag 'afs-fixes-20220802' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  afs: Fix access after dec in put functions
  afs: Use refcount_t rather than atomic_t

Pull setgid updates from Christian Brauner:
 "This contains the work to move setgid stripping out of individual
  filesystems and into the VFS itself.

  Creating files that have both the S_IXGRP and S_ISGID bit raised in
  directories that themselves have the S_ISGID bit set requires
  additional privileges to avoid security issues.

  When a filesystem creates a new inode it needs to take care that the
  caller is either in the group of the newly created inode or they have
  CAP_FSETID in their current user namespace and are privileged over the
  parent directory of the new inode. If any of these two conditions is
  true then the S_ISGID bit can be raised for an S_IXGRP file and if not
  it needs to be stripped.

  However, there are several key issues with the current implementation:

   - S_ISGID stripping logic is entangled with umask stripping.

     For example, if the umask removes the S_IXGRP bit from the file
     about to be created then the S_ISGID bit will be kept.

     The inode_init_owner() helper is responsible for S_ISGID stripping
     and is called before posix_acl_create(). So we can end up with two
     different orderings:

     1. FS without POSIX ACL support

        First strip umask then strip S_ISGID in inode_init_owner().

        In other words, if a filesystem doesn't support or enable POSIX
        ACLs then umask stripping is done directly in the vfs before
        calling into the filesystem:

     2. FS with POSIX ACL support

        First strip S_ISGID in inode_init_owner() then strip umask in
        posix_acl_create().

        In other words, if the filesystem does support POSIX ACLs then
        unmask stripping may be done in the filesystem itself when
        calling posix_acl_create().

     Note that technically filesystems are free to impose their own
     ordering between posix_acl_create() and inode_init_owner() meaning
     that there's additional ordering issues that influence S_ISGID
     inheritance.

     (Note that the commit message of commit 1639a49c ("fs: move
     S_ISGID stripping into the vfs_*() helpers") gets the ordering
     between inode_init_owner() and posix_acl_create() the wrong way
     around. I realized this too late.)

   - Filesystems that don't rely on inode_init_owner() don't get S_ISGID
     stripping logic.

     While that may be intentional (e.g. network filesystems might just
     defer setgid stripping to a server) it is often just a security
     issue.

     Note that mandating the use of inode_init_owner() was proposed as
     an alternative solution but that wouldn't fix the ordering issues
     and there are examples such as afs where the use of
     inode_init_owner() isn't possible.

     In any case, we should also try the cleaner and generalized
     solution first before resorting to this approach.

   - We still have S_ISGID inheritance bugs years after the initial
     round of S_ISGID inheritance fixes:

       e014f37d ("xfs: use setattr_copy to set vfs inode attributes")
       01ea173e ("xfs: fix up non-directory creation in SGID directories")
       fd84bfdd ("ceph: fix up non-directory creation in SGID directories")

  All of this led us to conclude that the current state is too messy.
  While we won't be able to make it completely clean as
  posix_acl_create() is still a filesystem specific call we can improve
  the S_SIGD stripping situation quite a bit by hoisting it out of
  inode_init_owner() and into the respective vfs creation operations.

  The obvious advantage is that we don't need to rely on individual
  filesystems getting S_ISGID stripping right and instead can
  standardize the ordering between S_ISGID and umask stripping directly
  in the VFS.

  A few short implementation notes:

   - The stripping logic needs to happen in vfs_*() helpers for the sake
     of stacking filesystems such as overlayfs that rely on these
     helpers taking care of S_ISGID stripping.

   - Security hooks have never seen the mode as it is ultimately seen by
     the filesystem because of the ordering issue we mentioned. Nothing
     is changed for them. We simply continue to strip the umask before
     passing the mode down to the security hooks.

   - The following filesystems use inode_init_owner() and thus relied on
     S_ISGID stripping: spufs, 9p, bfs, btrfs, ext2, ext4, f2fs,
     hfsplus, hugetlbfs, jfs, minix, nilfs2, ntfs3, ocfs2, omfs,
     overlayfs, ramfs, reiserfs, sysv, ubifs, udf, ufs, xfs, zonefs,
     bpf, tmpfs.

     We've audited all callchains as best as we could. More details can
     be found in the commit message to 1639a49c ("fs: move S_ISGID
     stripping into the vfs_*() helpers")"

* tag 'fs.setgid.v6.0' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  ceph: rely on vfs for setgid stripping
  fs: move S_ISGID stripping into the vfs_*() helpers
  fs: Add missing umask strip in vfs_tmpfile
  fs: add mode_strip_sgid() helper

Pull memblock updates from Mike Rapoport:

 - An optimization in memblock_add_range() to reduce array traversals

 - Improvements to the memblock test suite

* tag 'memblock-v5.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rppt/memblock:
  memblock test: Modify the obsolete description in README
  memblock tests: fix compilation errors
  memblock tests: change build options to run-time options
  memblock tests: remove completed TODO items
  memblock tests: set memblock_debug to enable memblock_dbg() messages
  memblock tests: add verbose output to memblock tests
  memblock tests: Makefile: add arguments to control verbosity
  memblock: avoid some repeat when add new range

Pull m68knommu fixes from Greg Ungerer:

 - spelling in comment

 - compilation when flexcan driver enabled

 - sparse warning

* tag 'm68knommu-for-v5.20' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu:
  m68k: Fix syntax errors in comments
  m68k: coldfire: make symbol m523x_clk_lookup static
  m68k: coldfire/device.c: protect FLEXCAN blocks

Pull x86 eIBRS fixes from Borislav Petkov:
 "More from the CPU vulnerability nightmares front:

  Intel eIBRS machines do not sufficiently mitigate against RET
  mispredictions when doing a VM Exit therefore an additional RSB,
  one-entry stuffing is needed"

* tag 'x86_bugs_pbrsb' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/speculation: Add LFENCE to RSB fill sequence
  x86/speculation: Add RSB VM Exit protections

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>

It's possible for a request to invalidate a fscache_cookie will come in
while we're already processing an invalidation. If that happens we
currently take an extra access reference that will leak. Only call
__fscache_begin_cookie_access if the FSCACHE_COOKIE_DO_INVALIDATE bit
was previously clear.

Also, ensure that we attempt to clear the bit when the cookie is
"FAILED" and put the reference to avoid an access leak.

Fixes: 85e4ea10 ("fscache: Fix invalidation/lookup race")
Suggested-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>

Pull ksmbd updates from Steve French:

 - fixes for memory access bugs (out of bounds access, oops, leak)

 - multichannel fixes

 - session disconnect performance improvement, and session register
   improvement

 - cleanup

* tag '5.20-rc-ksmbd-server-fixes' of git://git.samba.org/ksmbd:
  ksmbd: fix heap-based overflow in set_ntacl_dacl()
  ksmbd: prevent out of bound read for SMB2_TREE_CONNNECT
  ksmbd: prevent out of bound read for SMB2_WRITE
  ksmbd: fix use-after-free bug in smb2_tree_disconect
  ksmbd: fix memory leak in smb2_handle_negotiate
  ksmbd: fix racy issue while destroying session on multichannel
  ksmbd: use wait_event instead of schedule_timeout()
  ksmbd: fix kernel oops from idr_remove()
  ksmbd: add channel rwlock
  ksmbd: replace sessions list in connection with xarray
  MAINTAINERS: ksmbd: add entry for documentation
  ksmbd: remove unused ksmbd_share_configs_cleanup function

Pull more iov_iter updates from Al Viro:

 - more new_sync_{read,write}() speedups - ITER_UBUF introduction

 - ITER_PIPE cleanups

 - unification of iov_iter_get_pages/iov_iter_get_pages_alloc and
   switching them to advancing semantics

 - making ITER_PIPE take high-order pages without splitting them

 - handling copy_page_from_iter() for high-order pages properly

* tag 'pull-work.iov_iter-rebased' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (32 commits)
  fix copy_page_from_iter() for compound destinations
  hugetlbfs: copy_page_to_iter() can deal with compound pages
  copy_page_to_iter(): don't split high-order page in case of ITER_PIPE
  expand those iov_iter_advance()...
  pipe_get_pages(): switch to append_pipe()
  get rid of non-advancing variants
  ceph: switch the last caller of iov_iter_get_pages_alloc()
  9p: convert to advancing variant of iov_iter_get_pages_alloc()
  af_alg_make_sg(): switch to advancing variant of iov_iter_get_pages()
  iter_to_pipe(): switch to advancing variant of iov_iter_get_pages()
  block: convert to advancing variants of iov_iter_get_pages{,_alloc}()
  iov_iter: advancing variants of iov_iter_get_pages{,_alloc}()
  iov_iter: saner helper for page array allocation
  fold __pipe_get_pages() into pipe_get_pages()
  ITER_XARRAY: don't open-code DIV_ROUND_UP()
  unify the rest of iov_iter_get_pages()/iov_iter_get_pages_alloc() guts
  unify xarray_get_pages() and xarray_get_pages_alloc()
  unify pipe_get_pages() and pipe_get_pages_alloc()
  iov_iter_get_pages(): sanity-check arguments
  iov_iter_get_pages_alloc(): lift freeing pages array on failure exits into wrapper
  ...

had been broken for ITER_BVEC et.al. since ever (OK, v3.17 when
ITER_BVEC had first appeared)...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... since April 2021
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... just shove it into one pipe_buffer.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

now that we are advancing the iterator, there's no need to
treat the first page separately - just call append_pipe()
in a loop.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

mechanical change; will be further massaged in subsequent commits
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

here nothing even looks at the iov_iter after the call, so we couldn't
care less whether it advances or not.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

that one is somewhat clumsier than usual and needs serious testing.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and adjust the callers
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and untangle the cleanup on failure to add into pipe.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... doing revert if we end up not using some pages
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Most of the users immediately follow successful iov_iter_get_pages()
with advancing by the amount it had returned.

Provide inline wrappers doing that, convert trivial open-coded
uses of those.

BTW, iov_iter_get_pages() never returns more than it had been asked
to; such checks in cifs ought to be removed someday...
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

All call sites of get_pages_array() are essenitally identical now.
Replace with common helper...

Returns number of slots available in resulting array or 0 on OOM;
it's up to the caller to make sure it doesn't ask to zero-entry
array (i.e. neither maxpages nor size are allowed to be zero).
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

... and don't mangle maxsize there - turn the loop into counting
one instead.  Easier to see that we won't run out of array that
way.  Note that special treatment of the partial buffer in that
thing is an artifact of the non-advancing semantics of
iov_iter_get_pages() - if not for that, it would be append_pipe(),
same as the body of the loop that follows it.  IOW, once we make
iov_iter_get_pages() advancing, the whole thing will turn into
	calculate how many pages do we want
	allocate an array (if needed)
	call append_pipe() that many times.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

same as for pipes and xarrays; after that iov_iter_get_pages() becomes
a wrapper for __iov_iter_get_pages_alloc().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

same as for pipes
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

	The differences between those two are
* pipe_get_pages() gets a non-NULL struct page ** value pointing to
preallocated array + array size.
* pipe_get_pages_alloc() gets an address of struct page ** variable that
contains NULL, allocates the array and (on success) stores its address in
that variable.

	Not hard to combine - always pass struct page ***, have
the previous pipe_get_pages_alloc() caller pass ~0U as cap for
array size.
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

zero maxpages is bogus, but best treated as "just return 0";
NULL pages, OTOH, should be treated as a hard bug.

get rid of now completely useless checks in xarray_get_pages{,_alloc}().
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Incidentally, ITER_XARRAY did *not* free the sucker in case when
iter_xarray_populate_pages() returned 0...
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

All their callers are next to each other; all of them
want the total amount of pages and, possibly, the
offset in the partial final buffer.

Combine into a new helper (pipe_npages()), fix the
bogosity in pipe_space_for_user(), while we are at it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

We often need to find whether the last buffer is anon or not, and
currently it's rather clumsy:
	check if ->iov_offset is non-zero (i.e. that pipe is not empty)
	if so, get the corresponding pipe_buffer and check its ->ops
	if it's &default_pipe_buf_ops, we have an anon buffer.

Let's replace the use of ->iov_offset (which is nowhere near similar to
its role for other flavours) with signed field (->last_offset), with
the following rules:
	empty, no buffers occupied:		0
	anon, with bytes up to N-1 filled:	N
	zero-copy, with bytes up to N-1 filled:	-N

That way abs(i->last_offset) is equal to what used to be in i->iov_offset
and empty vs. anon vs. zero-copy can be distinguished by the sign of
i->last_offset.

	Checks for "should we extend the last buffer or should we start
a new one?" become easier to follow that way.

	Note that most of the operations can only be done in a sane
state - i.e. when the pipe has nothing past the current position of
iterator.  About the only thing that could be done outside of that
state is iov_iter_advance(), which transitions to the sane state by
truncating the pipe.  There are only two cases where we leave the
sane state:
	1) iov_iter_get_pages()/iov_iter_get_pages_alloc().  Will be
dealt with later, when we make get_pages advancing - the callers are
actually happier that way.
	2) iov_iter copied, then something is put into the copy.  Since
they share the underlying pipe, the original gets behind.  When we
decide that we are done with the copy (original is not usable until then)
we advance the original.  direct_io used to be done that way; nowadays
it operates on the original and we do iov_iter_revert() to discard
the excessive data.  At the moment there's nothing in the kernel that
could do that to ITER_PIPE iterators, so this reason for insane state
is theoretical right now.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Fold pipe_truncate() into it, clean up.  We can release buffers
in the same loop where we walk backwards to the iterator beginning
looking for the place where the new position will be.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

instead of setting ->iov_offset for new position and calling
pipe_truncate() to adjust ->len of the last buffer and discard
everything after it, adjust ->len at the same time we set ->iov_offset
and use pipe_discard_from() to deal with buffers past that.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

it's only used to get to the partial buffer we can add to,
and that's always the last one, i.e. pipe->head - 1.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

	Expand the only remaining call of push_pipe() (in
__pipe_get_pages()), combine it with the page-collecting loop there.

Note that the only reason it's not a loop doing append_pipe() is
that append_pipe() is advancing, while iov_iter_get_pages() is not.
As soon as it switches to saner semantics, this thing will switch
to using append_pipe().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>