This is a note to let you know that I've just added the patch titled
powerpc/64: Fix task_cpu in early boot when booting non-zero cpuid
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-64-fix-task_cpu-in-early-boot-when-booting-n.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 25a79a5199e1332eab0c9e63969ce0a2c26fc4ab
Author: Nicholas Piggin <npiggin@xxxxxxxxx>
Date: Fri Dec 16 21:59:28 2022 +1000
powerpc/64: Fix task_cpu in early boot when booting non-zero cpuid
[ Upstream commit 9fa24404f5044967753a6cd3e5e36f57686bec6e ]
powerpc/64 can boot on a non-zero SMP processor id. Initially, the boot
CPU is said to be "assumed to be 0" until early_init_devtree() discovers
the id from the device tree. That is not a good description because the
assumption can be wrong and that has to be handled, the better
description is that 0 is used as a placeholder, and things are fixed
after the real id is discovered.
smp_processor_id() is set to the boot cpuid, but task_cpu(current) is
not, which causes the smp_processor_id() == task_cpu(current) invariant
to be broken until init_idle() in sched_init().
This is quite fragile and could lead to subtle bugs in future. One bug
is that validate_sp_size uses task_cpu() to get the process stack, so
any stack trace from the booting CPU between early_init_devtree()
and sched_init() will have problems. Early on paca_ptrs[0] will be
poisoned, so that can cause machine checks dereferencing that memory
in real mode. Later, validating the current stack pointer against the
idle task of a different secondary will probably cause no stack trace
to be printed.
Fix this by setting thread_info->cpu right after smp_processor_id() is
set to the boot cpuid.
Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
[mpe: Fix SMP=n build as reported by sfr]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221216115930.2667772-3-npiggin@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index a0dee7354fe6b..a43865e0fb4bf 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -396,6 +396,11 @@ void __init early_setup(unsigned long dt_ptr)
}
fixup_boot_paca(paca_ptrs[boot_cpuid]);
setup_paca(paca_ptrs[boot_cpuid]); /* install the paca into registers */
+ // smp_processor_id() now reports boot_cpuid
+
+#ifdef CONFIG_SMP
+ task_thread_info(current)->cpu = boot_cpuid; // fix task_cpu(current)
+#endif
/*
* Configure exception handlers. This include setting up trampolines
