Date: Thu, 18 Jul 2002 11:40:02 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: John Baldwin <jhb@FreeBSD.ORG> Cc: current@FreeBSD.ORG Subject: Re: Questions about kern_descrip.c Message-ID: <200207181840.g6IIe25G019269@apollo.backplane.com> References: <XFMail.20020718134618.jhb@FreeBSD.org>
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: :In revision 1.94 of kern_descrip.c, in the dup2() syscall a goto :retry loop was added so that if we did a fdalloc() we always retested :everything. Since fd_nfiles can't shrink and new and old can't :change, I don't see why the loop is necessary. Neither dup() or :the F_DUPFD fcntl() were modified in this way either. Also, :calling fdalloc() in this case is somewhat bogus, because fdalloc() :is going to try and reserve an open slot and update variables such :as fd_lastfile, etc. appropriately. Perhaps we should have an :fdextend() function that both dup2() and fdalloc() call? Also, :in do_dup() you have commented out the call to munmapfd() on an :open file with UF_MAPPED and never turned it back on. Was that :intentional or just an accidental oversight? : :-- : :John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ The issue with dup2() was a race against open() or close() I believe, where dup2() could potentially dup into a descriptor that open() was about to use. Unfortunately, it does appear that dup() has the same issue. fdalloc() does not reserve the descriptor number it returns, it simply finds a free slot and says 'this index is a free slot'. Even in the latest -current, fdalloc() releases the fdp lock when it goes to MALLOC so the race appears to still be present. the munmap descriptor junk is obsolete and has not been used for a very long time. -Matt Matthew Dillon <dillon@backplane.com> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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