Date: Fri, 18 Nov 2005 07:30:56 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Ivo Janssen <ivo@ivo.nu> Cc: freebsd-amd64@FreeBSD.org Subject: Re: amd64/89202: Kernel crash when accessing filesystem Message-ID: <20051118071624.V96570@delplex.bde.org> In-Reply-To: <200511171820.jAHIKJef046199@freefall.freebsd.org> References: <200511171820.jAHIKJef046199@freefall.freebsd.org>
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On Thu, 17 Nov 2005, Ivo Janssen wrote: > I recreated the filesystem without the huge -f (avg filesize) option, > which we had initially set to 1Gb: > # newfs -U -O2 -b 8192 -f 1024 > # tunefs -e 20480 (10x the default) > > With the defaults of avg filesize of 16384, we don't see a crash. I > then started playing with tunefs. > Increasing the avg filesize to -f 16777216 (16Mb), we don't see a crash. > Increasing the avg filesize to -f 33554432 (32Mb), we repro the crash. I have had the following comment about this bug (but haven't fixed it) for many years % Index: ffs_alloc.c % =================================================================== % RCS file: /home/ncvs/src/sys/ufs/ffs/ffs_alloc.c,v % retrieving revision 1.121 % diff -u -2 -r1.121 ffs_alloc.c % --- ffs_alloc.c 16 Jun 2004 09:47:25 -0000 1.121 % +++ ffs_alloc.c 28 Oct 2004 15:12:47 -0000 % @@ -964,4 +991,11 @@ % minbfree = 1; % cgsize = fs->fs_fsize * fs->fs_fpg; % + /* % + * XXX the following multiplication can overflow, since newfs can % + * be abused to set fs_avgfilesize and fs_avgfpdir to preposterous % + * values. For the particular preposterous values of (64M, 16), % + * the multiplication overflows to 0 and then dirsize = 0 sometimes % + * causes division by 0. % + */ % dirsize = fs->fs_avgfilesize * fs->fs_avgfpdir; % curdirsize = avgndir ? (cgsize - avgbfree * fs->fs_bsize) / avgndir : 0; This bug is easy to work around by not changing fs->fs_avgfilesize or fs->fs_avgfpdir. Tuning them has limited useful effects. Bruce
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