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? -Eric > Thanks. > > ---- > > The size of s_mb_maxs that is defined in ext4_sb_info is too small. > When block size is 64K, which is possible on ia64, > the maximum value of s_mb_maxs becomes 256K(0x40000). > However, s_mb_maxs is defined as unsigned short. This is cause of panic. > > Signed-off-by: Yasunori Goto <y-goto@xxxxxxxxxxxxxx> > Cc: Li Zefan <lizf@xxxxxxxxxxxxxx> > Cc: Miao Xie <miaox@xxxxxxxxxxxxxx> > > --- > fs/ext4/ext4_sb.h | 3 ++- > fs/ext4/mballoc.c | 2 ++ > 2 files changed, 4 insertions(+), 1 deletion(-) > > Index: test2/fs/ext4/ext4_sb.h > =================================================================== > --- test2.orig/fs/ext4/ext4_sb.h 2008-12-16 11:20:18.000000000 +0900 > +++ test2/fs/ext4/ext4_sb.h 2008-12-16 14:17:32.000000000 +0900 > @@ -101,7 +101,8 @@ struct ext4_sb_info { > spinlock_t s_reserve_lock; > spinlock_t s_md_lock; > tid_t s_last_transaction; > - unsigned short *s_mb_offsets, *s_mb_maxs; > + unsigned short *s_mb_offsets; > + unsigned int *s_mb_maxs; > > /* tunables */ > unsigned long s_stripe; > Index: test2/fs/ext4/mballoc.c > =================================================================== > --- test2.orig/fs/ext4/mballoc.c 2008-12-16 11:20:18.000000000 +0900 > +++ test2/fs/ext4/mballoc.c 2008-12-16 14:23:21.000000000 +0900 > @@ -2493,6 +2493,8 @@ int ext4_mb_init(struct super_block *sb, > if (sbi->s_mb_offsets == NULL) { > return -ENOMEM; > } > + > + i = (sb->s_blocksize_bits + 2) * sizeof(unsigned int); > sbi->s_mb_maxs = kmalloc(i, GFP_KERNEL); > if (sbi->s_mb_maxs == NULL) { > kfree(sbi->s_mb_maxs); > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
