Re: [PATCH] fix race in AF_UNIX

[Thomas Graf <tgraf@suug.ch>]

* Thomas Graf <tgraf@suug.ch> 2007-06-18 12:32
> * Miklos Szeredi <miklos@szeredi.hu> 2007-06-18 11:44
> > Garbage collection only ever happens, if the app is sending AF_UNIX
> > sockets over AF_UNIX sockets.  Which is a rather rare case.  And which
> > is basically why this bug went unnoticed for so long.
> > 
> > So my second patch only affects the performance of _exactly_ those
> > apps which might well be bitten by the bug itself.
> 
> That's not entirely the truth. It affects all applications using
> AF_UNIX sockets while file descriptors are being transfered. I
> agree that the performance impact is not severe on most systems
> but if file descriptors are being transfered continously by just
> a single application it can become rather severe.

Also think of the scenario where an application, deliberately or not,
begins a file descriptor tranfser using sendmsg() and the receiving
part never invokes recvmsg() to decrement the inflight counters
again. Every unix socket that gets closed would result in a gc call
locking all sockets.