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From: "Yajun Deng" Message-ID: Subject: Re: [PATCH] mm/mm_init.c: remove spinlock in early_pfn_to_nid() To: "Greg KH" Cc: rafael@kernel.org, rppt@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org In-Reply-To: <2023061431-litigate-upchuck-7ed1@gregkh> References: <2023061431-litigate-upchuck-7ed1@gregkh> <20230614110324.3839354-1-yajun.deng@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: x6a1j8jsnwz7jk6zwki1r9h5qk863jhg X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D1840100006 X-HE-Tag: 1686742115-945338 X-HE-Meta: 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 ZZVoRE82 2Z4CmX4k2oKAKDTLZSfpiFvD1920tmo76pex1Lrc5o5EiRQCUz2EMajDD1UfHOrXPdXarNoBVsUllWAb1XpFrntsdp4qYriULzdGm897G63hqadFrEGzTqwNu6CYeWNDLUci8qToipCa8oK/82GJjhTItoXz4ZLkumvqqGpBWsUVt+dnCPsi6JzYEMgLL/kc6F0yh/yW/CNGBNdDxe54desspRi0M7UYz36sD5PgkJmHBMSQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: June 14, 2023 7:09 PM, "Greg KH" wrote:=0A= =0A> On Wed, Jun 14, 2023 at 07:03:24PM +0800, Yajun Deng wrote:=0A> =0A>= > When the system boots, only one cpu is enabled before smp_init().=0A>> = So the spinlock is not needed in most cases, remove it.=0A>> =0A>> Add sp= inlock in get_nid_for_pfn() because it is after smp_init().=0A> =0A> So t= his is two different things at once in the same patch?=0A> =0A> Or are th= ey the same problem and both need to go in to solve it?=0A> =0A> And if a= spinlock is not needed at early boot, is it really causing any=0A> probl= ems?=0A> =0A=0AThey are the same problem.=0AI added pr_info in early_pfn_= to_nid(), found get_nid_for_pfn() is the only=0Acase need to add spinlock= .=0AThis patch tested on my x86 system.=0A=0A=0A>> Signed-off-by: Yajun D= eng =0A>> ---=0A>> drivers/base/node.c | 11 +++++++= ++--=0A>> mm/mm_init.c | 18 +++---------------=0A>> 2 files changed, 12 i= nsertions(+), 17 deletions(-)=0A>> =0A>> diff --git a/drivers/base/node.c= b/drivers/base/node.c=0A>> index 9de524e56307..844102570ff2 100644=0A>> = --- a/drivers/base/node.c=0A>> +++ b/drivers/base/node.c=0A>> @@ -748,8 += 748,15 @@ int unregister_cpu_under_node(unsigned int cpu, unsigned int ni= d)=0A>> static int __ref get_nid_for_pfn(unsigned long pfn)=0A>> {=0A>> #= ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT=0A>> - if (system_state < SYSTEM_R= UNNING)=0A>> - return early_pfn_to_nid(pfn);=0A>> + static DEFINE_SPINLOC= K(early_pfn_lock);=0A>> + int nid;=0A>> +=0A>> + if (system_state < SYSTE= M_RUNNING) {=0A>> + spin_lock(&early_pfn_lock);=0A>> + nid =3D early_pfn_= to_nid(pfn);=0A>> + spin_unlock(&early_pfn_lock);=0A> =0A> Adding an exte= rnal lock for when you call a function is VERY dangerous=0A> as you did n= ot document this anywhere, and there's no way to enforce it=0A> properly = at all.=0A> =0A=0AI should add a comment before early_pfn_to_nid().=0A=0A= > Does your change actually result in any boot time changes? How was this= =0A> tested?=0A> =0A=0AJust a bit.=0A=0A> thanks,=0A> =0A> greg k-h