ext4: fix oops in trace_ext4_mb_release_group_pa

Our QA reported an oops in the ext4_mb_release_group_pa tracing,
and Josef Bacik pointed out that it was because we may have a
non-null but uninitialized ac_inode in the allocation context.

I can reproduce it when running xfstests with ext4 tracepoints on, 
on a CONFIG_SLAB_DEBUG kernel.

We call trace_ext4_mb_release_group_pa from 2 places, 
ext4_mb_discard_group_preallocations and 
ext4_mb_discard_lg_preallocations

In both cases we allocate an ac as a container just for tracing (!)
and never fill in the ac_inode.  There's no reason to be assigning,
testing, or printing it as far as I can see, so just remove it from
the tracepoint.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Josef Bacik <josef@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 0 insertions, 3 deletions

diff --git a/include/trace/events/ext4.h b/include/trace/events/ext4.h
index 6a1fcff95f7c..fbdfa3a6bbd8 100644
--- a/include/trace/events/ext4.h
+++ b/include/trace/events/ext4.h
@@ -432,7 +432,6 @@ TRACE_EVENT(ext4_mb_release_group_pa,
 
         TP_STRUCT__entry(
                 __field(        dev_t,  dev                     )
-                __field(        ino_t,  ino                     )
                 __field(        __u64,  pa_pstart               )
                 __field(        __u32,  pa_len                  )
 
@@ -440,8 +439,6 @@ TRACE_EVENT(ext4_mb_release_group_pa,
 
         TP_fast_assign(
                 __entry->dev            = sb->s_dev;
-                __entry->ino            = (ac && ac->ac_inode) ?
-                                                ac->ac_inode->i_ino : 0;
                 __entry->pa_pstart      = pa->pa_pstart;
                 __entry->pa_len         = pa->pa_len;
         ),