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Wed, 22 Nov 2023 13:12:16 -0800 (PST) Received: from fedora.mshome.net ([75.167.214.230]) by smtp.gmail.com with ESMTPSA id j18-20020a635512000000b005bdbce6818esm132136pgb.30.2023.11.22.13.12.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Nov 2023 13:12:16 -0800 (PST) From: Gregory Price X-Google-Original-From: Gregory Price To: linux-mm@kvack.org Cc: linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, arnd@arndb.de, tglx@linutronix.de, luto@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, mhocko@kernel.org, tj@kernel.org, ying.huang@intel.com, Gregory Price Subject: [RFC PATCH 04/11] mm/mempolicy: modify get_mempolicy call stack to take a task argument Date: Wed, 22 Nov 2023 16:11:53 -0500 Message-Id: <20231122211200.31620-5-gregory.price@memverge.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20231122211200.31620-1-gregory.price@memverge.com> References: <20231122211200.31620-1-gregory.price@memverge.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2BB5CA000F X-Stat-Signature: yrcdyhynodzo64666h46qfour77ar3dw X-Rspam-User: X-HE-Tag: 1700687537-189479 X-HE-Meta: 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 h7D+2QWv 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 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: List-Subscribe: List-Unsubscribe: To make mempolicy fetchable by external tasks, we must first change the callstack to take a task as an argument. Modify the following functions to require a task argument: do_get_mempolicy kernel_get_mempolicy The way the task->mm is acquired must change slightly to enable this change. Originally, do_get_mempolicy would acquire the task->mm directly via (current->mm). This is unsafe to do in a non-current context. However, utilizing get_task_mm would break the original functionality of do_get_mempolicy due to the following check in get_task_mm: if (mm) { if (task->flags & PF_KTHREAD) mm = NULL; else mmget(mm); } To retain the original behavior, if (task == current) we access the task->mm directly, but if (task != current) we will utilize get_task_mm to safely access the mm. We simplify the get/put mechanics by always taking a reference to the mm, even if we are in the context of (task == current). Additionally, since the mempolicy will become externally modifiable, we need to take the task lock to acquire task->mempolicy safely, regardless of whether we are operating on current or not. Signed-off-by: Gregory Price --- mm/mempolicy.c | 43 +++++++++++++++++++++++++++++-------------- 1 file changed, 29 insertions(+), 14 deletions(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 9ea3e1bfc002..4519f39b1a07 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -899,8 +899,9 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr) } /* Retrieve NUMA policy */ -static long do_get_mempolicy(int *policy, nodemask_t *nmask, - unsigned long addr, unsigned long flags) +static long do_get_mempolicy(struct task_struct *task, int *policy, + nodemask_t *nmask, unsigned long addr, + unsigned long flags) { int err; struct mm_struct *mm; @@ -915,9 +916,9 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, if (flags & (MPOL_F_NODE|MPOL_F_ADDR)) return -EINVAL; *policy = 0; /* just so it's initialized */ - task_lock(current); - *nmask = cpuset_current_mems_allowed; - task_unlock(current); + task_lock(task); + *nmask = task->mems_allowed; + task_unlock(task); return 0; } @@ -928,7 +929,16 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, * vma/shared policy at addr is NULL. We * want to return MPOL_DEFAULT in this case. */ - mm = current->mm; + if (task == current) { + /* + * original behavior allows a kernel task changing its + * own policy to avoid the condition in get_task_mm, + * so we'll directly access + */ + mm = task->mm; + mmget(mm); + } else + mm = get_task_mm(task); mmap_read_lock(mm); vma = vma_lookup(mm, addr); if (!vma) { @@ -947,8 +957,10 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, return -EINVAL; else { /* take a reference of the task policy now */ - pol = current->mempolicy; + task_lock(task); + pol = task->mempolicy; mpol_get(pol); + task_unlock(task); } if (!pol) { @@ -962,12 +974,13 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, vma = NULL; mmap_read_unlock(mm); err = lookup_node(mm, addr); + mmput(mm); if (err < 0) goto out; *policy = err; - } else if (pol == current->mempolicy && + } else if (pol == task->mempolicy && pol->mode == MPOL_INTERLEAVE) { - *policy = next_node_in(current->il_prev, pol->nodes); + *policy = next_node_in(task->il_prev, pol->nodes); } else { err = -EINVAL; goto out; @@ -987,9 +1000,9 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask, if (mpol_store_user_nodemask(pol)) { *nmask = pol->w.user_nodemask; } else { - task_lock(current); + task_lock(task); get_policy_nodemask(pol, nmask); - task_unlock(current); + task_unlock(task); } } @@ -1704,7 +1717,8 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, } /* Retrieve NUMA policy */ -static int kernel_get_mempolicy(int __user *policy, +static int kernel_get_mempolicy(struct task_struct *task, + int __user *policy, unsigned long __user *nmask, unsigned long maxnode, unsigned long addr, @@ -1719,7 +1733,7 @@ static int kernel_get_mempolicy(int __user *policy, addr = untagged_addr(addr); - err = do_get_mempolicy(&pval, &nodes, addr, flags); + err = do_get_mempolicy(task, &pval, &nodes, addr, flags); if (err) return err; @@ -1737,7 +1751,8 @@ SYSCALL_DEFINE5(get_mempolicy, int __user *, policy, unsigned long __user *, nmask, unsigned long, maxnode, unsigned long, addr, unsigned long, flags) { - return kernel_get_mempolicy(policy, nmask, maxnode, addr, flags); + return kernel_get_mempolicy(current, policy, nmask, maxnode, addr, + flags); } bool vma_migratable(struct vm_area_struct *vma) -- 2.39.1