Re: [PATCH v2 1/1] sched/numa: Fix memory leak due to the overwritten vma->numab_state

[Raghavendra K T <raghavendra.kt@amd.com>]

+ Vlastimil

Looks like he was unintentionally missed in CC. He has added Reviewed-by 
to V1

On 11/13/2024 3:51 PM, Adrian Huang wrote:
> From: Adrian Huang <ahuang12@lenovo.com>
> 
> [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/1794be3c-358c-4cdc-a43d-a1f841d91ef7@amd.com/
> 
> Fixes: ef6a22b70f6d ("sched/numa: apply the scan delay to every new vma")
> Reported-by: Jiwei Sun <sunjw10@lenovo.com>
> Signed-off-by: Adrian Huang <ahuang12@lenovo.com>
> Reviewed-by: Raghavendra K T <raghavendra.kt@amd.com>
> ---
>   kernel/sched/fair.c | 12 +++++++++---
>   1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 3356315d7e64..7f99df294583 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3399,10 +3399,16 @@ 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;
>