Hi Steffen, Herbert, this series solves multiple issues of padata I ran into while trying to make use of pcrypt for IPsec.
The first issue is that the reorder timer callback may run on a CPU that isn't part of the parallel set, as it runs on the CPU where the timer interrupt gets handled. As a result, padata_reorder() may run on a CPU with uninitialized per-cpu parallel queues, so the __this_cpu_read() in padata_get_next() refers to an uninitialized cpu_index. However, as per-cpu memory gets memset(0) on allocation time, it'll read 0. If the next CPU index we're waiting for is 0 too, the compare will succeed and we'll return with -ENODATA, making padata_reorder() think there's nothing to do, stop any pending timer and return immediately. This is wrong as the pending timer might have been the one to trigger the needed reordering, but, as it was canceled, will never happen -- if no other parallel requests arrive afterwards. That issue is addressed with the first two patches, ensuring we're not using a bogus cpu_index value for the compare and thereby not wrongly cancel a pending timer. The second patch then ensures the reorder timer callback runs on the correct CPU or, at least, on a CPU from the parallel set to generate forward progress. The third patch addresses a similar issues for the serialization callback. We implicitly require padata_do_serial() to be called on the very same CPU padata_do_parallel() was called on to ensure the correct ordering of requests -- and correct functioning of padata, even. If the algorithm we're parallelizing is asynchronous itself, that invariant might not be true, as, e.g. crypto hardware may execute the callback on the CPU its interrupt gets handled on which isn't necessarily the one the request got issued on. To handle that issue we track the CPU we're supposed to handle the request on and ensure we'll call padata_reorder() on that CPU when padata_do_serial() gets called -- either by already running on the corect CPU or by deferring the call to a worker. Please apply! Mathias Krause (3): padata: set cpu_index of unused CPUs to -1 padata: ensure the reorder timer callback runs on the correct CPU padata: ensure padata_do_serial() runs on the correct CPU include/linux/padata.h | 4 +++ kernel/padata.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 72 insertions(+), 3 deletions(-) -- 1.7.10.4
