Roland, can you please help with it? current utrace state is far from being stable, RHEL5 and -mm kernels can be quite easily crashed with some of the exploits we collected so far. Alexey can help you with any information needed - call traces, test cases, but without your help we can't fix it all ourselfes :/
Thanks, Kirill Alexey Dobriyan wrote: > The following patch fixes double free manifesting itself as crash in > __rcu_process_callbasks(): > http://marc.info/?l=linux-kernel&m=117518764517017&w=2 > https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=229112 > > The problem is with check_dead_utrace() conditionally scheduling > "struct utrace" for freeing but not cleaning struct task_struct::utrace > pointer leaving it reachable: > > tsk->utrace_flags = flags; > if (flags) > spin_unlock(&utrace->lock); > else > rcu_utrace_free(utrace); > > OTOH, utrace_release_task() first clears ->utrace pointer, then frees > struct utrace itself: > > Roland inserted some debugging into 2.6.21-rc6-mm1 so that aforementined > double free couldn't be reproduced without seeing > BUG at kernel/utrace.c:176 first. It triggers if one struct utrace were > passed to rcu_utrace_free() second time. > > With patch applied I no longer see¹ BUG message and double frees on > 2-way P3, 8-way ia64, Core 2 Duo boxes. Testcase is at the first link. > > I _think_ it adds leak if utrace_reap() takes branch without freeing > but, well, I hope Roland will give me some clue on how to fix it too. > > Signed-off-by: Alexey Dobriyan <[EMAIL PROTECTED]> > --- > > kernel/utrace.c | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) > > ¹ But I see whole can of other bugs! I think they were already lurking > but weren't easily reproducable without hitting double-free first. > FWIW, it's > BUG_ON(!list_empty(&tsk->ptracees)); > oops at the beginning of remove_engine() > NULL ->report_quiesce call which is absent in ptrace utrace ops > BUG_ON(tracehook_check_released(p)); > > --- a/kernel/utrace.c > +++ b/kernel/utrace.c > @@ -205,7 +205,6 @@ utrace_clear_tsk(struct task_struct *tsk > if (utrace->u.live.signal == NULL) { > task_lock(tsk); > if (likely(tsk->utrace != NULL)) { > - rcu_assign_pointer(tsk->utrace, NULL); > tsk->utrace_flags &= UTRACE_ACTION_NOREAP; > } > task_unlock(tsk); > @@ -305,10 +304,7 @@ check_dead_utrace(struct task_struct *ts > } > > tsk->utrace_flags = flags; > - if (flags) > - spin_unlock(&utrace->lock); > - else > - rcu_utrace_free(utrace); > + spin_unlock(&utrace->lock); > > /* > * Now we're finished updating the utrace state. > > _______________________________________________ > Devel mailing list > [EMAIL PROTECTED] > https://openvz.org/mailman/listinfo/devel > - 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/