linux-kernel - [PATCH 1/1] powerpc/crash: Use NMI context for printk after crashing other CPUs

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Message-Id: <20200406174058.686436-1-leonardo@linux.ibm.com>
Date:   Mon,  6 Apr 2020 14:40:59 -0300
From:   Leonardo Bras <leonardo@...ux.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Enrico Weigelt <info@...ux.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Allison Randal <allison@...utok.net>,
        Christophe Leroy <christophe.leroy@....fr>,
        Leonardo Bras <leonardo@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] powerpc/crash: Use NMI context for printk after crashing other CPUs

Currently, if printk lock (logbuf_lock) is held by other thread during
crash, there is a chance of deadlocking the crash on next printk, and
blocking a possibly desired kdump.

After sending IPI to all other CPUs, make printk enter in NMI context,
as it will use per-cpu buffers to store the message, and avoid locking
logbuf_lock.

Signed-off-by: Leonardo Bras <leonardo@...ux.ibm.com>
---
 arch/powerpc/kexec/crash.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kexec/crash.c b/arch/powerpc/kexec/crash.c
index d488311efab1..9b73e3991bf4 100644
--- a/arch/powerpc/kexec/crash.c
+++ b/arch/powerpc/kexec/crash.c
@@ -115,6 +115,7 @@ static void crash_kexec_prepare_cpus(int cpu)
 
 	crash_send_ipi(crash_ipi_callback);
 	smp_wmb();
+	printk_nmi_enter();
 
 again:
 	/*
-- 
2.25.1