Messages in this thread Patch in this message | | | Subject | Re: [PATCH v5] tracepoint: Do not fail unregistering a probe due to memory failure | From | Alexey Kardashevskiy <> | Date | Sat, 30 Jan 2021 23:30:18 +1100 |
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On 28/01/2021 09:07, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> > > The list of tracepoint callbacks is managed by an array that is protected > by RCU. To update this array, a new array is allocated, the updates are > copied over to the new array, and then the list of functions for the > tracepoint is switched over to the new array. After a completion of an RCU > grace period, the old array is freed. > > This process happens for both adding a callback as well as removing one. > But on removing a callback, if the new array fails to be allocated, the > callback is not removed, and may be used after it is freed by the clients > of the tracepoint. > > The handling of a failed allocation for removing an event can break use > cases as the error report is not propagated up to the original callers. To > make matters worse, there's some paths that can not handle error cases. > > Instead of allocating a new array for removing a tracepoint, allocate twice > the needed size when adding tracepoints to the array. On removing, use the > second half of the allocated array. This removes the need to allocate memory > for removing a tracepoint, as the allocation for removals will already have > been done. > > Link: https://lkml.kernel.org/r/20201115055256.65625-1-mmullins@mmlx.us > Link: https://lkml.kernel.org/r/20201116175107.02db396d@gandalf.local.home > Link: https://lkml.kennel.org/r/20201118093405.7a6d2290@gandalf.local.home > > Reported-by: Matt Mullins <mmullins@mmlx.us> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
I still need the following chunk (same "if (it_func_ptr)" as in the v2's reply) in order to stop crashes:
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 82eba6a05a1c..b7cf7a5a4f43 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -311,6 +311,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p) \ it_func_ptr = \ rcu_dereference_raw((&__tracepoint_##_name)->funcs); \ + if (it_func_ptr) \ do { \ it_func = (it_func_ptr)->func; \ __data = (it_func_ptr)->data; \
-- Alexey
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