Re: spinlock contention of files->file_lock

From: Linus Torvalds
Date: Mon Sep 30 2013 - 22:02:29 EST

On Mon, Sep 30, 2013 at 6:53 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> The problem is dup2()

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).

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.

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