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Re: amd64/89202: Kernel crash when accessing filesystem



I'm sure you've thought about this, but I can see the following
improvements to be made:

- make dirsize 64bit - add checks to the multiplication operation to make sure it doesn't
overflow at runtime
- add logic tunefs and newfs so that user cannot set values
that will lead to kernel panics
- add at the very least huge warnings to the newfs and tunefs
manpages, or mention why their usefulness is limited.


This particular partition is used for a huge postgres database, which
typically use files holding the actual tables. We assumed tuning the
fs would gain us some improvements...

-Ivo


On Fri, 18 Nov 2005, Bruce Evans wrote:

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



Ivo

--
+---------------------------------------------------------------------
| IVO JANSSEN - ivo at ivo.nu - http://ivo.nu/
| finger ivo at finger.ivo.nu for PGP and more info
| Part of the world's largest computer: http://www.distributed.net/
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