linux-kernel - [PATCH] risc-v: Fix order of IPI enablement vs RCU startup

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Message-Id: <20230703183126.1567625-1-maz@kernel.org>
Date:   Mon,  3 Jul 2023 19:31:26 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Conor Dooley <conor@...nel.org>,
        Anup Patel <apatel@...tanamicro.com>,
        Palmer Dabbelt <palmer@...osinc.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] risc-v: Fix order of IPI enablement vs RCU startup

Conor reports that risc-v tries to enable IPIs before telling the
core code to enable RCU. With the introduction of the mapple tree
as a backing store for the irq descriptors, this results in
a very shouty boot sequence, as RCU is legitimately upset.

Restore some sanity by moving the risc_ipi_enable() call after
notify_cpu_starting(), which explicitly enables RCU on the calling
CPU.

Fixes: 832f15f42646 ("RISC-V: Treat IPIs as normal Linux IRQs")
Reported-by: Conor Dooley <conor@...nel.org>
Signed-off-by: Marc Zyngier <maz@...nel.org>
Link: https://lore.kernel.org/r/20230703-dupe-frying-79ae2ccf94eb@spud
Cc: Anup Patel <apatel@...tanamicro.com>
Cc: Palmer Dabbelt <palmer@...osinc.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
---
 arch/riscv/kernel/smpboot.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index bb0b76e1a6d4..f4d6acb38dd0 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -238,10 +238,11 @@ asmlinkage __visible void smp_callin(void)
 	mmgrab(mm);
 	current->active_mm = mm;
 
-	riscv_ipi_enable();
-
 	store_cpu_topology(curr_cpuid);
 	notify_cpu_starting(curr_cpuid);
+
+	riscv_ipi_enable();
+
 	numa_add_cpu(curr_cpuid);
 	set_cpu_online(curr_cpuid, 1);
 	probe_vendor_features(curr_cpuid);
-- 
2.34.1