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Commit 541010e4 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'locks' of git://linux-nfs.org/~bfields/linux 

* 'locks' of git://linux-nfs.org/~bfields/linux:
  nfsd: remove IS_ISMNDLCK macro
  Rework /proc/locks via seq_files and seq_list helpers
  fs/locks.c: use list_for_each_entry() instead of list_for_each()
  NFS: clean up explicit check for mandatory locks
  AFS: clean up explicit check for mandatory locks
  9PFS: clean up explicit check for mandatory locks
  GFS2: clean up explicit check for mandatory locks
  Cleanup macros for distinguishing mandatory locks
  Documentation: move locks.txt in filesystems/
  locks: add warning about mandatory locking races
  Documentation: move mandatory locking documentation to filesystems/
  locks: Fix potential OOPS in generic_setlease()
  Use list_first_entry in locks_wake_up_blocks
  locks: fix flock_lock_file() comment
  Memory shortage can result in inconsistent flocks state
  locks: kill redundant local variable
  locks: reverse order of posix_locks_conflict() arguments
parents e457f790 5e7fc436

Documentation/00-INDEX

+1 −5
Original line number Diff line number Diff line
@@ -145,7 +145,7 @@ fb/ 
feature-removal-schedule.txt

	- list of files and features that are going to be removed.

filesystems/

	- directory with info on the various filesystems that Linux supports.

	- info on the vfs and the various filesystems that Linux supports.

firmware_class/

	- request_firmware() hotplug interface info.

floppy.txt
@@ -230,8 +230,6 @@ local_ops.txt 
	- semantics and behavior of local atomic operations.

lockdep-design.txt

	- documentation on the runtime locking correctness validator.

locks.txt

	- info on file locking implementations, flock() vs. fcntl(), etc.

logo.gif

	- full colour GIF image of Linux logo (penguin - Tux).

logo.txt
@@ -240,8 +238,6 @@ m68k/ 
	- directory with info about Linux on Motorola 68k architecture.

magic-number.txt

	- list of magic numbers used to mark/protect kernel data structures.

mandatory.txt

	- info on the Linux implementation of Sys V mandatory file locking.

mca.txt

	- info on supporting Micro Channel Architecture (e.g. PS/2) systems.

md.txt

Documentation/filesystems/00-INDEX

+4 −0
Original line number Diff line number Diff line
@@ -52,6 +52,10 @@ isofs.txt 
	- info and mount options for the ISO 9660 (CDROM) filesystem.

jfs.txt

	- info and mount options for the JFS filesystem.

locks.txt

	- info on file locking implementations, flock() vs. fcntl(), etc.

mandatory-locking.txt

	- info on the Linux implementation of Sys V mandatory file locking.

ncpfs.txt

	- info on Novell Netware(tm) filesystem using NCP protocol.

ntfs.txt

Documentation/locks.txt→Documentation/filesystems/locks.txt

+5 −5
Original line number Diff line number Diff line
@@ -53,11 +53,11 @@ fcntl(), with all the problems that implies. 
1.3 Mandatory Locking As A Mount Option

---------------------------------------



Mandatory locking, as described in 'Documentation/mandatory.txt' was prior

to this release a general configuration option that was valid for all

mounted filesystems. This had a number of inherent dangers, not the least

of which was the ability to freeze an NFS server by asking it to read a

file for which a mandatory lock existed.

Mandatory locking, as described in 'Documentation/filesystems/mandatory.txt'

was prior to this release a general configuration option that was valid for

all mounted filesystems.  This had a number of inherent dangers, not the

least of which was the ability to freeze an NFS server by asking it to read

a file for which a mandatory lock existed.



From this release of the kernel, mandatory locking can be turned on and off

on a per-filesystem basis, using the mount options 'mand' and 'nomand'.

Documentation/mandatory.txt→Documentation/filesystems/mandatory-locking.txt

+20 −1
Original line number Diff line number Diff line
@@ -3,7 +3,26 @@ 
		Andy Walker <andy@lysaker.kvaerner.no>



			   15 April 1996



		     (Updated September 2007)



0. Why you should avoid mandatory locking

-----------------------------------------



The Linux implementation is prey to a number of difficult-to-fix race

conditions which in practice make it not dependable:



	- The write system call checks for a mandatory lock only once

	  at its start.  It is therefore possible for a lock request to

	  be granted after this check but before the data is modified.

	  A process may then see file data change even while a mandatory

	  lock was held.

	- Similarly, an exclusive lock may be granted on a file after

	  the kernel has decided to proceed with a read, but before the

	  read has actually completed, and the reading process may see

	  the file data in a state which should not have been visible

	  to it.

	- Similar races make the claimed mutual exclusion between lock

	  and mmap similarly unreliable.



1. What is  mandatory locking?

------------------------------

fs/9p/vfs_file.c

+1 −1
Original line number Diff line number Diff line
@@ -105,7 +105,7 @@ static int v9fs_file_lock(struct file *filp, int cmd, struct file_lock *fl) 
	P9_DPRINTK(P9_DEBUG_VFS, "filp: %p lock: %p\n", filp, fl);



	/* No mandatory locks */

	if ((inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)

	if (__mandatory_lock(inode))

		return -ENOLCK;



	if ((IS_SETLK(cmd) || IS_SETLKW(cmd)) && fl->fl_type != F_UNLCK) {