linux-kernel - Re: [PATCH v2] locktorture: Fix memory leak in param_set

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Message-ID: <6719b1c4-3e7e-4c0f-aa80-a11dde0cf112@paulmck-laptop>
Date: Mon, 20 Oct 2025 14:52:45 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Wang Liang <wangliang74@...wei.com>
Cc: dave@...olabs.net, josh@...htriplett.org, frederic@...nel.org,
	yuehaibing@...wei.com, zhangchangzhong@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] locktorture: Fix memory leak in param_set_cpumask()

On Fri, Sep 26, 2025 at 11:57:17AM +0800, Wang Liang wrote:
> With CONFIG_CPUMASK_OFFSTACK=y, the 'bind_writers' buffer is allocated via
> alloc_cpumask_var() in param_set_cpumask(). But it is not freed, when
> setting the module parameter multiple times by sysfs interface or removing
> module.
> 
> Below kmemleak trace is seen for this issue:
> 
> unreferenced object 0xffff888100aabff8 (size 8):
>   comm "bash", pid 323, jiffies 4295059233
>   hex dump (first 8 bytes):
>     07 00 00 00 00 00 00 00                          ........
>   backtrace (crc ac50919):
>     __kmalloc_node_noprof+0x2e5/0x420
>     alloc_cpumask_var_node+0x1f/0x30
>     param_set_cpumask+0x26/0xb0 [locktorture]
>     param_attr_store+0x93/0x100
>     module_attr_store+0x1b/0x30
>     kernfs_fop_write_iter+0x114/0x1b0
>     vfs_write+0x300/0x410
>     ksys_write+0x60/0xd0
>     do_syscall_64+0xa4/0x260
>     entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> This issue can be reproduced by:
>   insmod locktorture.ko bind_writers=1
>   rmmod locktorture
> 
> or:
>   insmod locktorture.ko bind_writers=1
>   echo 2 > /sys/module/locktorture/parameters/bind_writers
> 
> Considering that setting the module parameter 'bind_writers' or
> 'bind_readers' by sysfs interface has no real effect, set the parameter
> permissions to 0444. To fix the memory leak when removing module, free
> 'bind_writers' and 'bind_readers' memory in lock_torture_cleanup().
> 
> Fixes: 73e341242483 ("locktorture: Add readers_bind and writers_bind module parameters")
> Suggested-by: Zhang Changzhong <zhangchangzhong@...wei.com>
> Signed-off-by: Wang Liang <wangliang74@...wei.com>

I have pulled this in for further review and testing, and please accept
my apologies for the delay.

							Thanx, Paul

> ---
>  kernel/locking/locktorture.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
> index ce0362f0a871..6567e5eeacc0 100644
> --- a/kernel/locking/locktorture.c
> +++ b/kernel/locking/locktorture.c
> @@ -103,8 +103,8 @@ static const struct kernel_param_ops lt_bind_ops = {
>  	.get = param_get_cpumask,
>  };
>  
> -module_param_cb(bind_readers, &lt_bind_ops, &bind_readers, 0644);
> -module_param_cb(bind_writers, &lt_bind_ops, &bind_writers, 0644);
> +module_param_cb(bind_readers, &lt_bind_ops, &bind_readers, 0444);
> +module_param_cb(bind_writers, &lt_bind_ops, &bind_writers, 0444);
>  
>  long torture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask, bool dowarn);
>  
> @@ -1211,6 +1211,10 @@ static void lock_torture_cleanup(void)
>  			cxt.cur_ops->exit();
>  		cxt.init_called = false;
>  	}
> +
> +	free_cpumask_var(bind_readers);
> +	free_cpumask_var(bind_writers);
> +
>  	torture_cleanup_end();
>  }
>  
> -- 
> 2.34.1
>