inode_nohighmem() is sufficient to make sure that page_get_link()
won't try to allocate a highmem page.  Moreover, it is sufficient
to make sure that page_symlink/__page_symlink won't do the same
thing.  However, any filesystem that manually preseeds the symlink's
page cache upon symlink(2) needs to make sure that the page it
inserts there won't be a highmem one.

Fortunately, only nfs and shmem have run afoul of that...

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

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

new method: ->get_link(); replacement of ->follow_link().  The differences
are:
	* inode and dentry are passed separately
	* might be called both in RCU and non-RCU mode;
the former is indicated by passing it a NULL dentry.
	* when called that way it isn't allowed to block
and should return ERR_PTR(-ECHILD) if it needs to be called
in non-RCU mode.

It's a flagday change - the old method is gone, all in-tree instances
converted.  Conversion isn't hard; said that, so far very few instances
do not immediately bail out when called in RCU mode.  That'll change
in the next commits.

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

kmap() in page_follow_link_light() needed to go - allowing to hold
an arbitrary number of kmaps for long is a great way to deadlocking
the system.

new helper (inode_nohighmem(inode)) needs to be used for pagecache
symlinks inodes; done for all in-tree cases.  page_follow_link_light()
instrumented to yell about anything missed.

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

Pull more vfs updates from Al Viro:
 "Assorted VFS fixes and related cleanups (IMO the most interesting in
  that part are f_path-related things and Eric's descriptor-related
  stuff).  UFS regression fixes (it got broken last cycle).  9P fixes.
  fs-cache series, DAX patches, Jan's file_remove_suid() work"

[ I'd say this is much more than "fixes and related cleanups".  The
  file_table locking rule change by Eric Dumazet is a rather big and
  fundamental update even if the patch isn't huge.   - Linus ]

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (49 commits)
  9p: cope with bogus responses from server in p9_client_{read,write}
  p9_client_write(): avoid double p9_free_req()
  9p: forgetting to cancel request on interrupted zero-copy RPC
  dax: bdev_direct_access() may sleep
  block: Add support for DAX reads/writes to block devices
  dax: Use copy_from_iter_nocache
  dax: Add block size note to documentation
  fs/file.c: __fget() and dup2() atomicity rules
  fs/file.c: don't acquire files->file_lock in fd_install()
  fs:super:get_anon_bdev: fix race condition could cause dev exceed its upper limitation
  vfs: avoid creation of inode number 0 in get_next_ino
  namei: make set_root_rcu() return void
  make simple_positive() public
  ufs: use dir_pages instead of ufs_dir_pages()
  pagemap.h: move dir_pages() over there
  remove the pointless include of lglock.h
  fs: cleanup slight list_entry abuse
  xfs: Correctly lock inode when removing suid and file capabilities
  fs: Call security_ops->inode_killpriv on truncate
  fs: Provide function telling whether file_remove_privs() will do anything
  ...

Mateusz Guzik reported :

 Currently obtaining a new file descriptor results in locking fdtable
 twice - once in order to reserve a slot and second time to fill it.

Holding the spinlock in __fd_install() is needed in case a resize is
done, or to prevent a resize.

Mateusz provided an RFC patch and a micro benchmark :
  http://people.redhat.com/~mguzik/pipebench.c

A resize is an unlikely operation in a process lifetime,
as table size is at least doubled at every resize.

We can use RCU instead of the spinlock.

__fd_install() must wait if a resize is in progress.

The resize must block new __fd_install() callers from starting,
and wait that ongoing install are finished (synchronize_sched())

resize should be attempted by a single thread to not waste resources.

rcu_sched variant is used, as __fd_install() and expand_fdtable() run
from process context.

It gives us a ~30% speedup using pipebench on a dual Intel(R) Xeon(R)
CPU E5-2696 v2 @ 2.50GHz

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Mateusz Guzik <mguzik@redhat.com>
Acked-by: Mateusz Guzik <mguzik@redhat.com>
Tested-by: Mateusz Guzik <mguzik@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Pull documentation updates from Jonathan Corbet:
 "The main thing here is Ingo's big subdirectory documenting feature
  support for each architecture.  Beyond that, it's the usual pile of
  fixes, tweaks, and small additions"

* tag 'docs-for-linus' of git://git.lwn.net/linux-2.6: (79 commits)
  doc:md: fix typo in md.txt.
  Documentation/mic/mpssd: don't build x86 userspace when cross compiling
  Documentation/prctl: don't build tsc tests when cross compiling
  Documentation/vDSO: don't build tests when cross compiling
  Doc:ABI/testing: Fix typo in sysfs-bus-fcoe
  Doc: Docbook: Change wikipedia's URL from http to https in scsi.tmpl
  Doc: Change wikipedia's URL from http to https
  Documentation/kernel-parameters: add missing pciserial to the earlyprintk
  Doc:pps: Fix typo in pps.txt
  kbuild : Fix documentation of INSTALL_HDR_PATH
  Documentation: filesystems: updated struct file_operations documentation in vfs.txt
  kbuild: edit explanation of clean-files variable
  Doc: ja_JP: Fix typo in HOWTO
  Move freefall program from Documentation/ to tools/
  Documentation: ARM: EXYNOS: Describe boot loaders interface
  Doc:nfc: Fix typo in nfc-hci.txt
  vfs: Minor documentation fix
  Doc: networking: txtimestamp: fix printf format warning
  Documentation, intel_pstate: Improve legacy mode internal governors description
  Documentation: extend use case for EXPORT_SYMBOL_GPL()
  ...

The check_acl inode operation and the IPERM_FLAG_RCU flag are long gone; update
the documentation.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

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

no remaining users

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