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[2003:cb:c707:fe00:bbeb:98e6:617a:dea1]) by smtp.gmail.com with ESMTPSA id bi7-20020a05600c3d8700b0038eb78569aasm5961159wmb.20.2022.04.29.02.54.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 29 Apr 2022 02:54:37 -0700 (PDT) Message-ID: Date: Fri, 29 Apr 2022 11:54:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH v2 1/4] mm/migration: reduce the rcu lock duration Content-Language: en-US To: Miaohe Lin , akpm@linux-foundation.org, mike.kravetz@oracle.com, naoya.horiguchi@nec.com Cc: ying.huang@intel.com, hch@lst.de, dhowells@redhat.com, cl@linux.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20220425132723.34824-1-linmiaohe@huawei.com> <20220425132723.34824-2-linmiaohe@huawei.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220425132723.34824-2-linmiaohe@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.04.22 15:27, Miaohe Lin wrote: > rcu_read_lock is required by grabbing the task refcount but it's not > needed for ptrace_may_access. So we could release the rcu lock after > task refcount is successfully grabbed to reduce the rcu holding time. > > Reviewed-by: Muchun Song > Reviewed-by: Christoph Hellwig > Signed-off-by: Miaohe Lin > Cc: Huang Ying > Cc: David Howells > Cc: Christoph Lameter > --- > mm/migrate.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index b2678279eb43..b779646665fe 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1902,17 +1902,16 @@ static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes) > return ERR_PTR(-ESRCH); > } > get_task_struct(task); > + rcu_read_unlock(); > > /* > * Check if this process has the right to modify the specified > * process. Use the regular "ptrace_may_access()" checks. > */ > if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { > - rcu_read_unlock(); > mm = ERR_PTR(-EPERM); > goto out; > } > - rcu_read_unlock(); > > mm = ERR_PTR(security_task_movememory(task)); > if (IS_ERR(mm)) Similar pattern in: mm/mempolicy.c:kernel_migrate_pages() kernel/futex/syscalls.c:get_robust_list() kernel/nsproxy.c:validate_nsset() Exception: sched/core_sched.c:sched_core_share_pid() Should we unify -- i.e., adjust the remaining 3 as well? -- Thanks, David / dhildenb