Messages in this thread | | | Date | Thu, 22 Jul 2010 13:45:08 +0800 | From | Li Zefan <> | Subject | Re: [BUG] ext4 trace events cause NULL pointer dereferences |
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Steven Rostedt wrote: > On Wed, 2010-07-21 at 22:31 +0900, KOSAKI Motohiro wrote: >> Hi Steven, > >> 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()? > > You could do: > > TP_fast_assign( > if (ac) { > __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; > }
This leaves __entry->dev etc as arbitrary value, since the entry returned by the ring buffer is not zeroed, so I think better add an else branch to zero those values.
> ), > > But this just makes the __entry null and wastes the ring buffer. > > I may be able to add a __discard_entry that may help. Then we could do > something like this: > > if (ac) { > __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; > } else > __discard_entry; > > Does this seem reasonable? > > But for now, the wasting the entry seems to be the only choice we have, > or to do as you suggested and have the "if (ac) trace_...", but I don't > like that. >
As I was (and still am) not sure what is the best fix, I decided to send out a bug report instead of a patch..
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