Date: Fri, 01 Feb 2002 17:02:12 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: Bruce Evans <bde@zeta.org.au> Cc: Alfred Perlstein <alfred@freebsd.org>, current@freebsd.org Subject: Re: lock reversal in fdalloc() Message-ID: <3C5B3A94.6B12B9D0@mindspring.com> References: <20020202072516.J290-100000@gamplex.bde.org>
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Bruce Evans wrote: > > basically it seems to get pissy if it doesn't get the file slot it asks > > for, so if another thread wins the race here, we'll panic. this problem > > seems to also exist for 4.x and previous versions of freebsd. > > > > I'd like to get this fixed. Any suggestions? I think simply > > removing the assertion should remove this hazzard, correct? I think if you delayed the allocation, it'd be OK, but I don't see a clean way to do it without a bit of work. > Something like that. This was apparently missed when the retry loop was > added. Lite2 has the panic but not the retry loop. > > BTW, the retry loop also picks up changes to the limit on descriptors. > In fdalloc(), the corresponding limit is treated as a loop invariant, > but it is not invariant. I think the process's rlimit can't change, > but maxfilesperproc can change even if the process doesn't block, since > it is not protected by FILEDESC_LOCK() :-(. Fortunately, the > maxfilesperproc limit isn't very important. I think this is a requirement. The problem is the case where the maxfilesperproc has *not* changed, and some other thread wins the race to the last one, you have to honor that, and fail the current attempt. Retries are fugly. 8-(. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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