(2013/07/19 22:33), Oleg Nesterov wrote: > On 07/19, Masami Hiramatsu wrote: >> >> (2013/07/18 23:51), Oleg Nesterov wrote: >>> It removes trace_array_get/put from tracing_open_generic_file() and >>> tracing_release_generic_file(). This assumes that "call->flags++" is >>> enough, but it is not. >> >> No, it replaces trace_array_get/put with ftrace_event_file_get/put >> which calls trace_array_get/put inside. > > Ah, I didn't notice your patch adds "file->tr->ref++" into > ftrace_event_file_get... > > So I was wrong in any case, thanks for correcting me. > > But, > >> (Just one point, previous ftrace_event_file_get has a racy point >> when it does tr->ref++, it should be fixed.) > > Not sure what do you mean, but unless I missed something again this > "tr->ref++" above still looks racy. instance_delete() checks tr->ref > first, then it takes event_mutex and removes/kfrees event_files. > > But this doesn't really matter even if I am right, surely this can > be fixed. My only point, imho this is more complex than necessary.
I see, so I'd like to see the fix. However, I'm not sure we have enough time to fix that cleanly. Note that except for the timing bug, we still leave a kernel bug which can easily be reproduced as Jovi reported. > In particular, > >>> IOW, I believe that either .open() should do trace_array_get(), or >>> __trace_remove_event_dirs() needs another for-each-file loop which >>> checks file->call->flags & TRACE_EVENT_FL_REF_MASK. >> >> Agreed :) > > Yes ;) and this makes the ref-counting even more complex, we use > different methods to avoid the races with rmdir and event_remove(). > >>> The same bugs which Steven's 1/4 tries to solve ;) >> >> OK, let me confirm that, would you mean we still need 2/4 - 4/4? > > Yes, yes. And those are depends on 1/4... Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
