Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=9efa68ed079af97f4e9477eadef567ffe64f7afc Commit: 9efa68ed079af97f4e9477eadef567ffe64f7afc Parent: 4f3b19ca41fbe572e3d44caf516c215b286fe2a6 Author: J. Bruce Fields <[EMAIL PROTECTED]> AuthorDate: Tue Sep 25 11:57:19 2007 -0400 Committer: J. Bruce Fields <[EMAIL PROTECTED]> CommitDate: Tue Oct 9 18:32:45 2007 -0400
locks: add warning about mandatory locking races The mandatory file locking implementation has long-standing races that probably render it useless. I know of no plans to fix them. Till we do, we should at least warn people. Signed-off-by: J. Bruce Fields <[EMAIL PROTECTED]> --- Documentation/filesystems/mandatory-locking.txt | 21 ++++++++++++++++++++- 1 files changed, 20 insertions(+), 1 deletions(-) diff --git a/Documentation/filesystems/mandatory-locking.txt b/Documentation/filesystems/mandatory-locking.txt index bc449d4..0979d1d 100644 --- a/Documentation/filesystems/mandatory-locking.txt +++ b/Documentation/filesystems/mandatory-locking.txt @@ -3,7 +3,26 @@ Andy Walker <[EMAIL PROTECTED]> 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? ------------------------------ - To unsubscribe from this list: send the line "unsubscribe git-commits-head" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html