Re: spinlock contention of files->file_lock

[Eric Dumazet]

On Tue, 2013-10-01 at 04:27 +0100, Al Viro wrote:
> On Mon, Sep 30, 2013 at 07:02:23PM -0700, Linus Torvalds wrote:
> 
> > Shouldn't a cmpxchg() in just the dup2 code solve that?
> > 
> > If the old value was NULL, you'd have to repeat and go back and see if
> > the open_fds[] bit had been cleared in the meantime (ie it's NULL not
> > because somebody else is busy installing it, but because somebody just
> > uninstalled it).
> 
> Yechh...  Under ->file_lock (in do_dup2()), hopefully?  Or you'll get
> all kinds of fun with close() thrown into the game, as well...
> 
> > But yeah, I do agree that that sounds nasty and a complication I
> > hadn't even thought about. dup2() does violate our normal "let's
> > pre-allocate the fd slot" rule. Ugh.
> 
> Hell knows...  Descriptor handling *is* pretty well isolated these
> days, so it just might be doable without disrupting the living hell
> out of anything else.  fs/file.c is pretty much it - everything else
> goes through it.

I have a patch mostly working here, and pretty short.

I'll do proper tests before posting it tomorrow.

 fs/fcntl.c              |    7 ++-----
 fs/file.c               |   17 +++++++++++++----
 fs/open.c               |   21 +++++++++++++++++----
 include/linux/fdtable.h |    1 +
 4 files changed, 33 insertions(+), 13 deletions(-)

Thanks !


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/