Messages in this thread | | | Subject | Re: [PATCH v2 1/4] mm/migration: reduce the rcu lock duration | From | Miaohe Lin <> | Date | Tue, 24 May 2022 20:36:52 +0800 |
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On 2022/4/29 17:54, David Hildenbrand wrote: > 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 <songmuchun@bytedance.com> >> Reviewed-by: Christoph Hellwig <hch@lst.de> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> Cc: Huang Ying <ying.huang@intel.com> >> Cc: David Howells <dhowells@redhat.com> >> Cc: Christoph Lameter <cl@linux.com> >> --- >> 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? >
I verified that this code change applies to kernel_migrate_pages(), but not get_robust_list() and validate_nsset(). It's because task_struct reference is not grabbed for later ones. Will send the new patch soon.
Thanks!
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