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Date:   Tue, 09 Nov 2021 11:46:01 +1000
From:   Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] powerpc/pseries/cpuhp: Use alloc_cpumask_var() in
 pseries_cpu_hotplug_init()
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        =?iso-8859-1?q?Daniel=0A?= Henrique Barboza 
        <danielhb413@gmail.com>, Waiman Long <longman@redhat.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nathan Lynch <nathanl@linux.ibm.com>,
        Paul Mackerras <paulus@samba.org>
Cc:     =?iso-8859-1?q?Laurent=0A?= Dufour <ldufour@linux.ibm.com>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        =?iso-8859-1?q?Zhang=0A?= Xiaoxu <zhangxiaoxu5@huawei.com>
References: <20211108164751.65565-1-longman@redhat.com>
        <87y25ym96i.fsf@mpe.ellerman.id.au>
In-Reply-To: <87y25ym96i.fsf@mpe.ellerman.id.au>
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Excerpts from Michael Ellerman's message of November 9, 2021 11:04 am:
> Waiman Long <longman@redhat.com> writes:
>> It was found that the following warning message could be printed out whe=
n
>> booting the kernel on PowerPC systems that support LPAR:
>>
>> [    0.129584] WARNING: CPU: 0 PID: 1 at mm/memblock.c:1451 memblock_all=
oc_internal+0x5c/0x104
>> [    0.129593] Modules linked in:
>> [    0.129598] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.14.0-11.el9.p=
pc64le+debug #1
>> [    0.129605] NIP:  c000000002040134 LR: c00000000204011c CTR: c0000000=
020241a8
>> [    0.129610] REGS: c000000005637760 TRAP: 0700   Not tainted  (5.14.0-=
11.el9.ppc64le+debug)
>> [    0.129616] MSR:  8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 48=
000222  XER: 00000002
>> [    0.129635] CFAR: c0000000004d1cf4 IRQMASK: 0
>> [    0.129635] GPR00: c00000000204011c c000000005637a00 c000000002c94d00=
 0000000000000001
>> [    0.129635] GPR04: 0000000000000080 0000000000000000 0000000000000000=
 ffffffffffffffff
>> [    0.129635] GPR08: 0000000000000000 0000000000000003 c00000000205ac64=
 0000000000080000
>> [    0.129635] GPR12: 0000000000000000 c0000000049d0000 c000000000013078=
 0000000000000000
>> [    0.129635] GPR16: 0000000000000000 0000000000000000 0000000000000000=
 0000000000000000
>> [    0.129635] GPR20: 0000000000000000 0000000000000000 0000000000000000=
 0000000000000000
>> [    0.129635] GPR24: c000000002003808 c00000000146f7b8 0000000000000000=
 0000000000000100
>> [    0.129635] GPR28: c000000002d7cf80 0000000000000000 0000000000000008=
 0000000000000000
>> [    0.129710] NIP [c000000002040134] memblock_alloc_internal+0x5c/0x104
>> [    0.129717] LR [c00000000204011c] memblock_alloc_internal+0x44/0x104
>> [    0.129723] Call Trace:
>> [    0.129726] [c000000005637a00] [c000000005637a40] 0xc000000005637a40 =
(unreliable)
>> [    0.129735] [c000000005637a60] [c0000000020404d8] memblock_alloc_try_=
nid+0x94/0xcc
>> [    0.129743] [c000000005637af0] [c00000000205ac64] alloc_bootmem_cpuma=
sk_var+0x4c/0x9c
>> [    0.129751] [c000000005637b60] [c0000000020242e0] __machine_initcall_=
pseries_pseries_cpu_hotplug_init+0x138/0x1d8
>> [    0.129760] [c000000005637bf0] [c000000000012404] do_one_initcall+0xa=
4/0x4f0
>> [    0.129768] [c000000005637cd0] [c000000002005358] do_initcalls+0x140/=
0x18c
>> [    0.129776] [c000000005637d80] [c0000000020055b8] kernel_init_freeabl=
e+0x178/0x1d0
>> [    0.129783] [c000000005637db0] [c0000000000130a0] kernel_init+0x30/0x=
190
>> [    0.129790] [c000000005637e10] [c00000000000cef4] ret_from_kernel_thr=
ead+0x5c/0x64
>>
>> The warning is printed in memblock_alloc_internal() because the slab
>> has been initialized when the initcalls are being processed. To
>> avoid the warning, change alloc_bootmem_cpumask_var() call in
>> pseries_cpu_hotplug_init() to alloc_cpumask_var() instead. Also
>> change cpumask_or() to cpumask_copy() or we will have to use
>> zalloc_cpumask_var().
>>
>> Fixes: bd1dd4c5f528 ("powerpc/pseries: Prevent free CPU ids being reused=
 on another node")
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>>  arch/powerpc/platforms/pseries/hotplug-cpu.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>=20
>=20
> This looks similar to the patch Nick sent recently:
>=20
>   https://lore.kernel.org/linuxppc-dev/20211105132923.1582514-1-npiggin@g=
mail.com/

Ah, you get CONFIG_CPUMASK_OFFSTACK=3Dy if CONFIG_DEBUG_PER_CPU_MAPS=3Dy.
I was wondering how Waiman found it.

Differences between the two patches are error checking - no big deal but=20
we should just do it. And GFP_NOWAIT - is this required here?

Thanks,
Nick