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Mon, 28 Sep 2026 10:42:01 -0700 (PDT) Date: Mon, 28 Sep 2026 17:41:18 +0000 In-Reply-To: <20260928174122.3380703-1-smostafa@google.com> Mime-Version: 1.0 References: <20260928174122.3380703-1-smostafa@google.com> X-Mailer: git-send-email 2.56.0.rc1.315.gc6ed9934b7-goog Message-ID: <20260928174122.3380703-12-smostafa@google.com> Subject: [RFC PATCH 11/15] fork: Move vmap stack freeing to work queue From: Mostafa Saleh To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org, linux-rt-devel@lists.linux.dev Cc: corbet@lwn.net, skhan@linuxfoundation.org, rdunlap@infradead.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, akpm@linux-foundation.org, urezki@gmail.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, kees@kernel.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, gustavoars@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, David Stevens , Mostafa Saleh Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260928_104203_727032_032B5781 X-CRM114-Status: GOOD ( 14.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: David Stevens For vmap stacks not immediately released into the stack cache, free them in a workqueue instead of via call_rcu(). In an RCU context, vfree already schedules the actual freeing on the per-cpu system workqueue, so this change only affects when exactly the second attempt to put the stack into the stack cache occurs. Moving freeing to a workqueue will allow for freeing partially populated stacks in a sleepable context (for remove_vm_area), rather than relying on vfree dispatching to a workqueue via vfree_atomic. Signed-off-by: David Stevens [Use system_percpu_wq instead of system_wq as it is deprecated and update commit msg] Signed-off-by: Mostafa Saleh --- kernel/fork.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 3f1c46d8f7ec..ca8e68882316 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -208,7 +208,7 @@ static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]); #define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO | __GFP_SKIP_KASAN) struct vm_stack { - struct rcu_head rcu; + struct rcu_work work; struct vm_struct *stack_vm_area; }; @@ -287,9 +287,9 @@ static inline void free_vmap_stack(struct vm_struct *vm_area) vfree(vm_area->addr); } -static void thread_stack_free_rcu(struct rcu_head *rh) +static void thread_stack_free_work(struct work_struct *work) { - struct vm_stack *vm_stack = container_of(rh, struct vm_stack, rcu); + struct vm_stack *vm_stack = container_of(to_rcu_work(work), struct vm_stack, work); struct vm_struct *vm_area = vm_stack->stack_vm_area; if (try_release_thread_stack_to_cache(vm_stack->stack_vm_area)) @@ -308,7 +308,8 @@ static void thread_stack_delayed_free(struct task_struct *tsk) vm_stack = tsk->stack + THREAD_SIZE - sizeof(*vm_stack); vm_stack->stack_vm_area = tsk->stack_vm_area; - call_rcu(&vm_stack->rcu, thread_stack_free_rcu); + INIT_RCU_WORK(&vm_stack->work, thread_stack_free_work); + queue_rcu_work(system_percpu_wq, &vm_stack->work); } static int free_vm_stack_cache(unsigned int cpu) -- 2.56.0.rc1.315.gc6ed9934b7-goog