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[107.220.129.194]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-6604e6a5b44sm261601d50.10.2026.05.28.16.10.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2026 16:10:46 -0700 (PDT) From: Matt Turner To: linux-alpha@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Richard Henderson , Magnus Lindholm , Matt Turner , stable@vger.kernel.org Subject: [PATCH] alpha: Fix SMP shutdown hang due to missing memory barriers Date: Thu, 28 May 2026 19:10:43 -0400 Message-ID: <20260528231043.1842326-1-mattst88@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Alpha has a very weak memory model. halt() makes no guarantee that pending stores have drained from the store buffer. If set_cpu_present() stores are still buffered when a secondary CPU halts, they are lost, and the boot CPU spins forever in the cpu_present_mask wait loop. Add mb() before halt() on secondary CPUs to flush the store buffer, and use smp_mb() in the boot CPU's poll loop instead of the compiler-only barrier() to ensure it observes secondary CPUs' stores. This avoids a deadlock on shutdown on EV7/Marvel platforms. Cc: stable@vger.kernel.org Assisted-by: Claude:claude-sonnet-4-6 Signed-off-by: Matt Turner Reviewed-by: Magnus Lindholm Tested-by: Magnus Lindholm --- arch/alpha/kernel/process.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git ./arch/alpha/kernel/process.c ./arch/alpha/kernel/process.c index 06522451f018..d50f9cfd8333 100644 --- ./arch/alpha/kernel/process.c +++ ./arch/alpha/kernel/process.c @@ -99,6 +99,7 @@ common_shutdown_1(void *generic_ptr) *pflags =3D flags; set_cpu_present(cpuid, false); set_cpu_possible(cpuid, false); + mb(); halt(); } #endif @@ -127,7 +128,7 @@ common_shutdown_1(void *generic_ptr) set_cpu_present(boot_cpuid, false); set_cpu_possible(boot_cpuid, false); while (!cpumask_empty(cpu_present_mask)) - barrier(); + smp_mb(); #endif =20 /* If booted from SRM, reset some of the original environment. */ --=20 2.53.0