rseq: Protect rseq_reset() against interrupts

rseq: Protect rseq_reset() against interrupts

rseq_reset() uses memset() to clear the tasks rseq data. That's racy
against membarrier() and preemption.

Guard it with irqsave to cure this.

Fixes: faba9d250eae ("rseq: Introduce struct rseq_data")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Link: https://patch.msgid.link/20260428224427.353887714%40kernel.org
Cc: stable@vger.kernel.org