Re: [OOPs] ext4: fixpoint divide exception at ext4_fill_super+0x141c/0x2908

[Nageswara R Sastry <rnsastry@linux.vnet.ibm.com>]

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Hi,

The following bug exists in 2.6.32-rc* also.

 > ------------[ cut here ]------------
 > Kernel BUG at 000003e00429d934 [verbose debug info unavailable]
 > fixpoint divide exception: 0009 [#1] SMP

Please find the patch which solves the following 'fixpoint divide 
exception'. I tested the same and not seeing any KERNEL BUG/exception.

I created the patch from 2.6.32-rc6 code.


Thanks and Regards
R.Nageswara Sastry

Though the 'sbi->s_log_groups_per_flex' contains valid data after the 
shift operation 'groups_per_flex' is becoming zero, which later used as 
a divisor.
groups_per_flex = 1 << sbi->s_log_groups_per_flex

Signed-off-by: Nageswara R Sastry <rnsastry@linux.vnet.ibm.com>




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diff -Naurp a/linux-2.6.32-rc6/fs/ext4/super.c b/linux-2.6.32-rc6/fs/ext4/super.c
--- a/linux-2.6.32-rc6/fs/ext4/super.c	2009-11-03 20:37:49.000000000 +0100
+++ b/linux-2.6.32-rc6/fs/ext4/super.c	2009-11-04 13:21:48.000000000 +0100
@@ -1681,6 +1681,12 @@ static int ext4_fill_flex_info(struct su
 	sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
 	groups_per_flex = 1 << sbi->s_log_groups_per_flex;
 
+	/* There are some situations, after shift the value of 'groups_per_flex'
+	   can become zero and division with 0 will result in fixpoint divide exception
+	 */
+	if (groups_per_flex == 0)
+		return 1;
+
 	/* We allocate both existing and potentially added groups */
 	flex_group_count = ((sbi->s_groups_count + groups_per_flex - 1) +
 			((le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) + 1) <<