Messages in this thread | | | Subject | Re: [xfs-masters] Re: filesystem corruption on xfs after 2.6.25-rc1 (bisected, powerpc related?) | From | Johannes Berg <> | Date | Tue, 26 Feb 2008 19:11:32 +0100 |
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> I debuged this a bit further by testing the 4 changed functions > individually. The problem only occurs with the new version of > xfs_lowbit64.
Eh, uh, of course. Now that I look at that code it becomes obvious.
find_first_bit() works on unsigned longs, not 64-bit quantities, so find_first_bit((unsigned long *)&t, 64) isn't equivalent to finding the lowest bit set in a 64-bit quantity.
Think of the memory layout of a 64-bit word:
LE: low 32 bits | high 32 bits BE: high 32 bits | low 32 bits
Take a look at the start of include/asm-powerpc/bitops.h, and note how bitops don't define the memory layout at all :)
So find_first_bit(&t, 64) on BE will give you the number of the first bit of the 32-bit rotated quantity, ie. of ((t<<32) | (t>>32)).
The problem doesn't happen with highbit64 because fls64 was specifically coded for this purpose.
You really need to keep xfs_lowbit64 defined as it was before, or, maybe even better, define ffs64 in parallel to fls64.
johannes [unhandled content-type:application/pgp-signature] | |