Date: Sat, 3 Jan 2009 20:21:08 +0200 From: Jaakko Heinonen <jh@saunalahti.fi> To: freebsd-fs@freebsd.org Subject: [patch] ext2fs freeze/corruption on amd64 Message-ID: <20090103182107.GA4119@a91-153-125-115.elisa-laajakaista.fi>
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Hi, I can quite easily reproduce a hard freeze while writing to an ext2fs filesystem on amd64. I can reliably reproduce it by building a kernel with "make -j2" on ext2fs. This has been reported by other people too: http://lists.freebsd.org/pipermail/freebsd-fs/2008-March/004504.html http://lists.freebsd.org/pipermail/freebsd-bugs/2008-January/027555.html http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/119529 http://www.freebsd.org/cgi/query-pr.cgi?pr=amd64/99561 I tracked the problem down to find_next_zero_bit() in ext2_bitops.h. The bug doesn't affect i386 because it uses asm bitops from i386-bitops.h. (There's also sparc64-bitops.h file but it's not used anywhere.) The problem is that if the offset (ofs) has one or more of it's five low bits set those bits are incorrectly re-added to the result. With following patch applied I can't reproduce the problem. %%% Index: sys/gnu/fs/ext2fs/ext2_bitops.h =================================================================== --- sys/gnu/fs/ext2fs/ext2_bitops.h (revision 186639) +++ sys/gnu/fs/ext2fs/ext2_bitops.h (working copy) @@ -84,7 +84,7 @@ find_next_zero_bit(void *data, size_t sz mask = ~0U << (ofs & 31); bit = *p | ~mask; if (bit != ~0U) - return (ffs(~bit) + ofs - 1); + return (ffs(~bit) + (ofs & ~31U) - 1); p++; ofs = (ofs + 31U) & ~31U; } %%% I hope that someone would commit this or similar fix. It might be also reasonable to delete the unused sparc64-bitops.h file. -- Jaakko
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