On Wed, Nov 04, 2009 at 07:24:04PM +0530, Nageswara R Sastry wrote: > Seems to be I have a little format related issue with the patch. So > resending it. Please accept my apologies. > Sachin thanks for letting me know. > >> > ------------[ 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. Nageswara, Thanks for sending this patch. The problem with it is that it leaves sbi->s_log_groups_per_flex non-zero, but it leaves sbi->s_flex_groups unallocated. This should lead to number of kernel oops caused by a null pointer dereference if there is any attempt to allocate blocks or inodes, or to resize the filesystem. A better fix is would be: ext4: Avoid divide by zero when trying to mount a corrupted file system If s_log_groups_per_flex is greater than 31, then groups_per_flex will will overflow and cause a divide by zero error. This can cause kernel BUG if such a file system is mounted. Thanks to Nageswara R Sastry for analyzing the failure and providing an initial patch. http://bugzilla.kernel.org/show_bug.cgi?id=14287 Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx> diff --git a/fs/ext4/super.c b/fs/ext4/super.c index d4ca92a..8662b2e 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -1673,14 +1673,14 @@ static int ext4_fill_flex_info(struct super_block *sb) size_t size; int i; - if (!sbi->s_es->s_log_groups_per_flex) { + sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex; + groups_per_flex = 1 << sbi->s_log_groups_per_flex; + + if (groups_per_flex < 2) { sbi->s_log_groups_per_flex = 0; return 1; } - sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex; - groups_per_flex = 1 << sbi->s_log_groups_per_flex; - /* 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) << -- 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
