Messages in this thread | | | Date | Wed, 21 Jul 2010 16:21:16 +0200 | From | Frederic Weisbecker <> | Subject | Re: [BUG] ext4 trace events cause NULL pointer dereferences |
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On Wed, Jul 21, 2010 at 10:16:06AM -0400, 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; > } > ), > > 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. > > -- Steve
Is there no already existing branch in ext4 you could reuse in order to send the trace only if (ac) ?
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