From f6cc0c50164994afd538911603b4a8f8029aeba7 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 16 Aug 2018 11:45:50 +0100 Subject: [PATCH] arm64: Avoid calling stop_machine() when patching jump labels Patching a jump label involves patching a single instruction at a time, swizzling between a branch and a NOP. The architecture treats these instructions specially, so a concurrently executing CPU is guaranteed to see either the NOP or the branch, rather than an amalgamation of the two instruction encodings. However, in order to guarantee that the new instruction is visible, it is necessary to send an IPI to the concurrently executing CPU so that it discards any previously fetched instructions from its pipeline. This operation therefore cannot be completed from a context with IRQs disabled, but this is exactly what happens on the jump label path where the hotplug lock is held and irqs are subsequently disabled by stop_machine_cpuslocked(). This results in a deadlock during boot on Hikey-960. Due to the architectural guarantees around patching NOPs and branches, we don't actually need to stop_machine() at all on the jump label path, so we can avoid the deadlock by using the "nosync" variant of our instruction patching routine. Fixes: 693350a79980 ("arm64: insn: Don't fallback on nosync path for general insn patching") Reported-by: Tuomas Tynkkynen Reported-by: John Stultz Tested-by: Valentin Schneider Tested-by: Tuomas Tynkkynen Tested-by: John Stultz Signed-off-by: Will Deacon --- arch/arm64/kernel/jump_label.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/kernel/jump_label.c b/arch/arm64/kernel/jump_label.c index c2dd1ad..e075641 100644 --- a/arch/arm64/kernel/jump_label.c +++ b/arch/arm64/kernel/jump_label.c @@ -36,7 +36,7 @@ void arch_jump_label_transform(struct jump_entry *entry, insn = aarch64_insn_gen_nop(); } - aarch64_insn_patch_text(&addr, &insn, 1); + aarch64_insn_patch_text_nosync(addr, insn); } void arch_jump_label_transform_static(struct jump_entry *entry, -- 2.7.4