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SubjectRe: [Patch/BUG] (ext4) s_mb_maxs[] of ext4_sb_info is too small size
> Yasunori Goto wrote:
> > Hello.
> >
> > I chased the cause of following ext4 oops report which is tested on
> > ia64 box.
> >
> > http://bugzilla.kernel.org/show_bug.cgi?id=12018
> >
> > The cause is the size of s_mb_maxs array that is
> > defined as "unsigned short" in ext4_sb_info structure.
> > Unsigned short is too small.
> >
> > In this bug report, Li-san formatted with 64Kbyte block size like
> > the following. Ia64 has 64Kbyte page size, then this
> > block size is acceptable.
> >
> > # mkfs.ext4 -b 65536 /dev/md0
> >
> > In this case, the maximum value of s_mb_maxs[] becomes
> > (blocksize << 2) = 256K by the following code.
> >
> > 2482 int ext4_mb_init(struct super_block *sb, int needs_recovery)
> > :
> > :
> > 2508 max = sb->s_blocksize << 2; <---- max becomes 0x40000.
> > 2509 do {
> > 2510 sbi->s_mb_offsets[i] = offset;
> > 2511 sbi->s_mb_maxs[i] = max; <--- over flow!!!
> > 2512 offset += 1 << (sb->s_blocksize_bits - i);
> > 2513 max = max >> 1;
> > 2514 i++;
> > 2515 } while (i <= sb->s_blocksize_bits + 1);
> >
> > Then, some s_mb_maxs[] becomes 0 due to overflow.
> > It is cause of this oops. The following patch is to fix it.
>
> Looks good to mee; and these lines before it:
>
> sbi->s_mb_maxs[0] = sb->s_blocksize << 3;
> sbi->s_mb_offsets[0] = 0;
>
> mean that we would have a problem "even" on 8k blocks, yes?

Oh, Yes. :-)

Thanks.

--
Yasunori Goto




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