On Sun, 28 Oct 2007 13:43:21 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote: > From: J. Bruce Fields <bfields@xxxxxxxxxxxxxx> > > We currently attempt to return -EDEALK to blocking fcntl() file locking > requests that would create a cycle in the graph of tasks waiting on > locks. > > This is inefficient: in the general case it requires us determining > whether we're adding a cycle to an arbitrary directed acyclic graph. > And this calculation has to be performed while holding a lock (currently > the BKL) that prevents that graph from changing. > > It has historically been a source of bugs; most recently it was noticed > that it could loop indefinitely while holding the BKL. > > It seems unlikely to be useful to applications: > - The difficulty of implementation has kept standards from > requiring it. (E.g. SUSv3 : "Since implementation of full > deadlock detection is not always feasible, the [EDEADLK] error > was made optional.") So portable applications may not be able to > depend on it. > - It only detects deadlocks that involve nothing but local posix > file locks; deadlocks involving network filesystems or other kinds > of locks or resources are missed. > > It therefore seems best to remove deadlock detection. > > Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxxxxxx> NAK. This is an ABI change and one that was rejected before when this was last discussed in detail. Moving it out of BKL makes a ton of sense, even adding a "don't check" flag makes a lot of sense. Removing the checking does not. I'd much rather see if (flags & FL_NODLCHECK) posix_deadlock_detect(....) The failure case for removing this feature is obscure and hard to debug application hangs for the afflicted programs - not nice for users at all. Alan - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
