rseq: Extend struct rseq with numa node id

Adding the NUMA node id to struct rseq is a straightforward thing to do,
and a good way to figure out if anything in the user-space ecosystem
prevents extending struct rseq.

This NUMA node id field allows memory allocators such as tcmalloc to
take advantage of fast access to the current NUMA node id to perform
NUMA-aware memory allocation.

It can also be useful for implementing fast-paths for NUMA-aware
user-space mutexes.

It also allows implementing getcpu(2) purely in user-space.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221122203932.231377-5-mathieu.desnoyers@efficios.com

diff --git a/include/trace/events/rseq.h b/include/trace/events/rseq.h
index a04a64bc1a000422f6480521fd74a7b65756893c..dde7a359b4ef1f2f3ef2774ec1086e63b50bc20c 100644 (file)
--- a/include/trace/events/rseq.h
+++ b/include/trace/events/rseq.h
@@ -16,13 +16,15 @@ TRACE_EVENT(rseq_update,
 
        TP_STRUCT__entry(
                __field(s32, cpu_id)
+               __field(s32, node_id)
        ),
 
        TP_fast_assign(
                __entry->cpu_id = raw_smp_processor_id();
+               __entry->node_id = cpu_to_node(__entry->cpu_id);
        ),
 
-       TP_printk("cpu_id=%d", __entry->cpu_id)
+       TP_printk("cpu_id=%d node_id=%d", __entry->cpu_id, __entry->node_id)
 );
 
 TRACE_EVENT(rseq_ip_fixup,

diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index 05d3c4cdeb40e6e7544d24f46e2564b20037f4cf..1cb90a435c5c33c83014f1d447517674d8a780ab 100644 (file)
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -131,6 +131,14 @@ struct rseq {
         */
        __u32 flags;
 
+       /*
+        * Restartable sequences node_id field. Updated by the kernel. Read by
+        * user-space with single-copy atomicity semantics. This field should
+        * only be read by the thread which registered this data structure.
+        * Aligned on 32-bit. Contains the current NUMA node ID.
+        */
+       __u32 node_id;
+
        /*
         * Flexible array member at end of structure, after last feature field.
         */

diff --git a/kernel/rseq.c b/kernel/rseq.c
index 7962738455c9a94584c080d131ec6b7615daa13f..193cfcc94ddcf80b3993f446d89bc3de592da834 100644 (file)
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -85,15 +85,17 @@
  *   F1. <failure>
  */
 
-static int rseq_update_cpu_id(struct task_struct *t)
+static int rseq_update_cpu_node_id(struct task_struct *t)
 {
-       u32 cpu_id = raw_smp_processor_id();
        struct rseq __user *rseq = t->rseq;
+       u32 cpu_id = raw_smp_processor_id();
+       u32 node_id = cpu_to_node(cpu_id);
 
        if (!user_write_access_begin(rseq, t->rseq_len))
                goto efault;
        unsafe_put_user(cpu_id, &rseq->cpu_id_start, efault_end);
        unsafe_put_user(cpu_id, &rseq->cpu_id, efault_end);
+       unsafe_put_user(node_id, &rseq->node_id, efault_end);
        /*
         * Additional feature fields added after ORIG_RSEQ_SIZE
         * need to be conditionally updated only if
@@ -109,9 +111,9 @@ efault:
        return -EFAULT;
 }
 
-static int rseq_reset_rseq_cpu_id(struct task_struct *t)
+static int rseq_reset_rseq_cpu_node_id(struct task_struct *t)
 {
-       u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED;
+       u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED, node_id = 0;
 
        /*
         * Reset cpu_id_start to its initial state (0).
@@ -125,6 +127,11 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t)
         */
        if (put_user(cpu_id, &t->rseq->cpu_id))
                return -EFAULT;
+       /*
+        * Reset node_id to its initial state (0).
+        */
+       if (put_user(node_id, &t->rseq->node_id))
+               return -EFAULT;
        /*
         * Additional feature fields added after ORIG_RSEQ_SIZE
         * need to be conditionally reset only if
@@ -314,7 +321,7 @@ void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs)
                if (unlikely(ret < 0))
                        goto error;
        }
-       if (unlikely(rseq_update_cpu_id(t)))
+       if (unlikely(rseq_update_cpu_node_id(t)))
                goto error;
        return;
 
@@ -361,7 +368,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
                        return -EINVAL;
                if (current->rseq_sig != sig)
                        return -EPERM;
-               ret = rseq_reset_rseq_cpu_id(current);
+               ret = rseq_reset_rseq_cpu_node_id(current);
                if (ret)
                        return ret;
                current->rseq = NULL;