[PATCH] powerpc: Set paca->data_offset = 0 for boot cpu
Aneesh Kumar K.V
aneesh.kumar at linux.vnet.ibm.com
Fri Sep 21 18:37:15 EST 2012
Michael Ellerman <michael at ellerman.id.au> writes:
> In commit 407821a we assigned a poison value to the paca->data_offset.
> Unfortunately with CONFIG_LOCK_STAT=y lockdep will read & write to percpu
> data very early in boot, prior to us initialising the percpu areas,
> leading to a crash.
> We have been getting away with this because the data_offset was previously
> set to zero. This causes lockdep to read & write to the initial copy of
> the percpu variables, which are discarded later in boot.
> Although that is "fishy", it does work, and for lock statistics it is no
> big deal to discard the counts from early boot.
> So set the paca->data_offset = 0 for the boot cpu paca only.
> Reported-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> Signed-off-by: Michael Ellerman <michael at ellerman.id.au>
Tested-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> arch/powerpc/kernel/setup_64.c | 2 ++
> 1 file changed, 2 insertions(+)
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 389bd4f..efb6a41 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -208,6 +208,8 @@ void __init early_setup(unsigned long dt_ptr)
> /* Fix up paca fields required for the boot cpu */
> get_paca()->cpu_start = 1;
> + /* Allow percpu accesses to "work" until we setup percpu data */
> + get_paca()->data_offset = 0;
> /* Probe the machine type */
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