linux.git/fs/file_table.c, branch v3.14

vfs: atomic f_pos accesses as per POSIX

2014-03-10T15:44:41+00:00

Our write() system call has always been atomic in the sense that you get
the expected thread-safe contiguous write, but we haven't actually
guaranteed that concurrent writes are serialized wrt f_pos accesses, so
threads (or processes) that share a file descriptor and use "write()"
concurrently would quite likely overwrite each others data.

This violates POSIX.1-2008/SUSv4 Section XSI 2.9.7 that says:

 "2.9.7 Thread Interactions with Regular File Operations

  All of the following functions shall be atomic with respect to each
  other in the effects specified in POSIX.1-2008 when they operate on
  regular files or symbolic links: [...]"

and one of the effects is the file position update.

This unprotected file position behavior is not new behavior, and nobody
has ever cared.  Until now.  Yongzhi Pan reported unexpected behavior to
Michael Kerrisk that was due to this.

This resolves the issue with a f_pos-specific lock that is taken by
read/write/lseek on file descriptors that may be shared across threads
or processes.

Reported-by: Yongzhi Pan 
Reported-by: Michael Kerrisk 
Cc: Al Viro 
Signed-off-by: Linus Torvalds 
Signed-off-by: Al Viro

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2013-11-13T06:34:18+00:00

Pull vfs updates from Al Viro:
 "All kinds of stuff this time around; some more notable parts:

   - RCU'd vfsmounts handling
   - new primitives for coredump handling
   - files_lock is gone
   - Bruce's delegations handling series
   - exportfs fixes

  plus misc stuff all over the place"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (101 commits)
  ecryptfs: ->f_op is never NULL
  locks: break delegations on any attribute modification
  locks: break delegations on link
  locks: break delegations on rename
  locks: helper functions for delegation breaking
  locks: break delegations on unlink
  namei: minor vfs_unlink cleanup
  locks: implement delegations
  locks: introduce new FL_DELEG lock flag
  vfs: take i_mutex on renamed file
  vfs: rename I_MUTEX_QUOTA now that it's not used for quotas
  vfs: don't use PARENT/CHILD lock classes for non-directories
  vfs: pull ext4's double-i_mutex-locking into common code
  exportfs: fix quadratic behavior in filehandle lookup
  exportfs: better variable name
  exportfs: move most of reconnect_path to helper function
  exportfs: eliminate unused "noprogress" counter
  exportfs: stop retrying once we race with rename/remove
  exportfs: clear DISCONNECTED on all parents sooner
  exportfs: more detailed comment for path_reconnect
  ...

get rid of s_files and files_lock

2013-11-09T05:16:20+00:00

The only thing we need it for is alt-sysrq-r (emergency remount r/o)
and these days we can do just as well without going through the
list of files.

Signed-off-by: Al Viro

file->f_op is never NULL...

2013-10-25T03:34:54+00:00

Signed-off-by: Al Viro

nfsd regression since delayed fput()

2013-10-20T12:44:39+00:00

Background: nfsd v[23] had throughput regression since delayed fput
went in; every read or write ends up doing fput() and we get a pair
of extra context switches out of that (plus quite a bit of work
in queue_work itselfi, apparently).  Use of schedule_delayed_work()
gives it a chance to accumulate a bit before we do __fput() on all
of them.  I'm not too happy about that solution, but... on at least
one real-world setup it reverts about 10% throughput loss we got from
switch to delayed fput.

Signed-off-by: Al Viro

fs/file_table.c:fput(): make comment more truthful

2013-09-11T22:59:01+00:00

Cc: "Eric W. Biederman" 
Cc: Andrey Vagin 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

only regular files with FMODE_WRITE need to be on s_files

2013-09-04T02:50:28+00:00

Signed-off-by: Al Viro

fput: turn "list_head delayed_fput_list" into llist_head

2013-07-13T09:29:10+00:00

fput() and delayed_fput() can use llist and avoid the locking.

This is unlikely path, it is not that this change can improve
the performance, but this way the code looks simpler.

Signed-off-by: Oleg Nesterov 
Suggested-by: Andrew Morton 
Cc: Al Viro 
Cc: Andrey Vagin 
Cc: "Eric W. Biederman" 
Cc: David Howells 
Cc: Huang Ying 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Al Viro

fs/file_table.c:fput(): add comment

2013-07-13T09:27:42+00:00

A missed update to "fput: task_work_add() can fail if the caller has
passed exit_task_work()".

Cc: "Eric W. Biederman" 
Cc: Al Viro 
Cc: Andrey Vagin 
Cc: David Howells 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Al Viro

Replace a bunch of file->dentry->d_inode refs with file_inode()

2013-06-29T08:57:13+00:00

Replace a bunch of file->dentry->d_inode refs with file_inode().

In __fput(), use file->f_inode instead so as not to be affected by any tricks
that file_inode() might grow.

Signed-off-by: David Howells 
Signed-off-by: Al Viro