FAILED: patch "[PATCH] sched/numa: fix memory leak due to the overwritten" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 5f1b64e9a9b7ee9cfd32c6b2fab796e29bfed075
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024121049-manhandle-nintendo-724e@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5f1b64e9a9b7ee9cfd32c6b2fab796e29bfed075 Mon Sep 17 00:00:00 2001
From: Adrian Huang <[email protected]>
Date: Wed, 13 Nov 2024 18:21:46 +0800
Subject: [PATCH] sched/numa: fix memory leak due to the overwritten
vma->numab_state

[Problem Description]
When running the hackbench program of LTP, the following memory leak is reported by kmemleak.

  # /opt/ltp/testcases/bin/hackbench 20 thread 1000
  Running with 20*40 (== 800) tasks.

  # dmesg | grep kmemleak
  ...
  kmemleak: 480 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
  kmemleak: 665 new suspected memory leaks (see /sys/kernel/debug/kmemleak)

  # cat /sys/kernel/debug/kmemleak
  unreferenced object 0xffff888cd8ca2c40 (size 64):
    comm "hackbench", pid 17142, jiffies 4299780315
    hex dump (first 32 bytes):
      ac 74 49 00 01 00 00 00 4c 84 49 00 01 00 00 00  .tI.....L.I.....
      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    backtrace (crc bff18fd4):
      [<ffffffff81419a89>] __kmalloc_cache_noprof+0x2f9/0x3f0
      [<ffffffff8113f715>] task_numa_work+0x725/0xa00
      [<ffffffff8110f878>] task_work_run+0x58/0x90
      [<ffffffff81ddd9f8>] syscall_exit_to_user_mode+0x1c8/0x1e0
      [<ffffffff81dd78d5>] do_syscall_64+0x85/0x150
      [<ffffffff81e0012b>] entry_SYSCALL_64_after_hwframe+0x76/0x7e
  ...

This issue can be consistently reproduced on three different servers:
* a 448-core server
* a 256-core server
* a 192-core server

[Root Cause]
Since multiple threads are created by the hackbench program (along with the command argument 'thread'), a shared vma might be accessed by two or more cores simultaneously. When two or more cores observe that vma->numab_state is NULL at the same time, vma->numab_state will be overwritten.

Although current code ensures that only one thread scans the VMAs in a single 'numa_scan_period', there might be a chance for another thread to enter in the next 'numa_scan_period' while we have not gotten till numab_state allocation [1].

Note that the command /opt/ltp/testcases/bin/hackbench 50 process 1000 cannot the reproduce the issue. It is verified with 200+ test runs.

[Solution]
Use the cmpxchg atomic operation to ensure that only one thread executes the vma->numab_state assignment.

[1] https://lore.kernel.org/lkml/[email protected]/

index fbdca89c677f..a59ae2e23daf 100644
@@ -3399,11 +3399,17 @@ static void task_numa_work(struct callback_head *work)
 
 		/* Initialise new per-VMA NUMAB state. */
 		if (!vma->numab_state) {
-			vma->numab_state = kzalloc(sizeof(struct vma_numab_state),
-				GFP_KERNEL);
-			if (!vma->numab_state)
+			struct vma_numab_state *ptr;
+
+			ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
+			if (!ptr)
 				continue;
 
+			if (cmpxchg(&vma->numab_state, NULL, ptr)) {
+				kfree(ptr);
+				continue;
+			}
+
 			vma->numab_state->start_scan_seq = mm->numa_scan_seq;
 
 			vma->numab_state->next_scan = now +