Patch "bpf: Initialize same number of free nodes for each pcpu_freelist" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf: Initialize same number of free nodes for each pcpu_freelist

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-initialize-same-number-of-free-nodes-for-each-pc.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1223d4692d437bef78b58a20e13851452f582821
Author: Xu Kuohai <xukuohai@xxxxxxxxxx>
Date:   Thu Nov 10 07:21:28 2022 -0500

    bpf: Initialize same number of free nodes for each pcpu_freelist
    
    [ Upstream commit 4b45cd81f737d79d0fbfc0d320a1e518e7f0bbf0 ]
    
    pcpu_freelist_populate() initializes nr_elems / num_possible_cpus() + 1
    free nodes for some CPUs, and then possibly one CPU with fewer nodes,
    followed by remaining cpus with 0 nodes. For example, when nr_elems == 256
    and num_possible_cpus() == 32, CPU 0~27 each gets 9 free nodes, CPU 28 gets
    4 free nodes, CPU 29~31 get 0 free nodes, while in fact each CPU should get
    8 nodes equally.
    
    This patch initializes nr_elems / num_possible_cpus() free nodes for each
    CPU firstly, then allocates the remaining free nodes by one for each CPU
    until no free nodes left.
    
    Fixes: e19494edab82 ("bpf: introduce percpu_freelist")
    Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
    Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
    Acked-by: Yonghong Song <yhs@xxxxxx>
    Link: https://lore.kernel.org/bpf/20221110122128.105214-1-xukuohai@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
index 3d897de89061..bbab8bb4b2fd 100644
--- a/kernel/bpf/percpu_freelist.c
+++ b/kernel/bpf/percpu_freelist.c
@@ -102,22 +102,21 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
 			    u32 nr_elems)
 {
 	struct pcpu_freelist_head *head;
-	int i, cpu, pcpu_entries;
+	unsigned int cpu, cpu_idx, i, j, n, m;
 
-	pcpu_entries = nr_elems / num_possible_cpus() + 1;
-	i = 0;
+	n = nr_elems / num_possible_cpus();
+	m = nr_elems % num_possible_cpus();
 
+	cpu_idx = 0;
 	for_each_possible_cpu(cpu) {
-again:
 		head = per_cpu_ptr(s->freelist, cpu);
-		/* No locking required as this is not visible yet. */
-		pcpu_freelist_push_node(head, buf);
-		i++;
-		buf += elem_size;
-		if (i == nr_elems)
-			break;
-		if (i % pcpu_entries)
-			goto again;
+		j = n + (cpu_idx < m ? 1 : 0);
+		for (i = 0; i < j; i++) {
+			/* No locking required as this is not visible yet. */
+			pcpu_freelist_push_node(head, buf);
+			buf += elem_size;
+		}
+		cpu_idx++;
 	}
 }