Re: [RFC,PATCH] use rcu for fasync_lock

[Manfred Spraul]

Linus Torvalds wrote:

> Here's a big clue: if you make code worse than it is today, it won't be 
> accepted. I don't even see why you'd bother in the first place.
>  
fasync_helper != kill_fasync
fasync_helper is rare, and usually running under lock_kernel().
kill_fasync is far more common (every pipe_read and _write), I want to 
remove the unconditional read_lock(&global_lock).

> So go back to the drawing board, and just do it _right_. Or don't do it at 
> all. There's no point to making the code look and behave worse than it 
> does today.
Today's solution is two copies of fasync_helper: one with lock_sock in 
net/socket.c, one with write_lock_irq(&fasync_lock) in fs/fcntl.c.

Perhaps just a "if (*fp == NULL) return;" before grabbing the read_lock 
in kill_fasync, without touching fasync_helper - that would be 
sufficient to fix pipe_read and _write.

--
   Manfred

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