Hi Steven,
> create file: file_108.dat
> # sync
> (panic)
>
>
> Seems ac->ac_inode can be NULL:
>
> DECLARE_EVENT_CLASS(ext4__mballoc,
> ...
> TP_fast_assign(
> __entry->dev = ac->ac_inode->i_sb->s_dev;
> __entry->ino = ac->ac_inode->i_ino;
> ...
> ),
> ...
> );
Can you teach us proper tracepint writing way?
ext4_mb_release_group_pa() has a concern when ac is NULL.
============================================================
static noinline_for_stack int
ext4_mb_release_group_pa(struct ext4_buddy *e4b,
struct ext4_prealloc_space *pa,
struct ext4_allocation_context *ac)
{
struct super_block *sb = e4b->bd_sb;
ext4_group_t group;
ext4_grpblk_t bit;
trace_ext4_mb_release_group_pa(ac, pa);
BUG_ON(pa->pa_deleted == 0);
ext4_get_group_no_and_offset(sb, pa->pa_pstart, &group, &bit);
BUG_ON(group != e4b->bd_group && pa->pa_len != 0);
mb_free_blocks(pa->pa_inode, e4b, bit, pa->pa_len);
atomic_add(pa->pa_len, &EXT4_SB(sb)->s_mb_discarded);
if (ac) { // here
ac->ac_sb = sb;
ac->ac_inode = NULL;
ac->ac_b_ex.fe_group = group;
ac->ac_b_ex.fe_start = bit;
ac->ac_b_ex.fe_len = pa->pa_len;
ac->ac_b_ex.fe_logical = 0;
trace_ext4_mballoc_discard(ac);
}
return 0;
}
===================================================
but trace_ext4_mb_release_group_pa() doesn't care it.
=====================================================
TRACE_EVENT(ext4_mb_release_group_pa,
TP_PROTO(struct ext4_allocation_context *ac,
struct ext4_prealloc_space *pa),
TP_ARGS(ac, pa),
TP_STRUCT__entry(
__field( dev_t, dev )
__field( ino_t, ino )
__field( __u64, pa_pstart )
__field( __u32, pa_len )
),
TP_fast_assign(
__entry->dev = ac->ac_sb->s_dev;
__entry->ino = ac->ac_inode->i_ino;
__entry->pa_pstart = pa->pa_pstart;
__entry->pa_len = pa->pa_len;
),
TP_printk("dev %s pstart %llu len %u",
jbd2_dev_to_name(__entry->dev), __entry->pa_pstart, __entry->pa_len)
);
=====================================================
So, adding following branch should fix this issue.
if (ac)
trace_ext4_mb_release_group_pa(ac, pa);
But, I don't think this is proper fix because we don't want any overhead
if the tracepoint is disabled.
So, How do we check NULL in TP_fast_assign()?
Thanks.
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