On 11/07/2017 10:38 PM, Kees Cook wrote:
> The mutex in sysctl_vm_numa_stat_handler() needs to be a global static, not
> a stack variable, otherwise it doesn't serve any purpose. Also, reading the
> file with CONFIG_LOCKDEP=y will complain:
Oops, good catch.
> [ 63.258593] INFO: trying to register non-static key.
> [ 63.259113] the code is fine but needs lockdep annotation.
> [ 63.259596] turning off the locking correctness validator.
> [ 63.260073] CPU: 1 PID: 4102 Comm: perl Not tainted
> 4.14.0-rc8-next-20171107+ #419
> [ 63.260769] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> Ubuntu-1.8.2-1ubuntu1 04/01/2014
> [ 63.261570] Call Trace:
> [ 63.261783] dump_stack+0x5f/0x86
> [ 63.262062] register_lock_class+0xe4/0x550
> [ 63.262408] ? __lock_acquire+0x308/0x1170
> [ 63.262746] __lock_acquire+0x7e/0x1170
> [ 63.263063] lock_acquire+0x9d/0x1d0
> [ 63.263363] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
> [ 63.263777] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
> [ 63.264192] __mutex_lock+0xb8/0x9a0
> [ 63.264488] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
> [ 63.264942] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
> [ 63.265398] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
> [ 63.265840] sysctl_vm_numa_stat_handler+0x8f/0x2d0
> [ 63.266270] proc_sys_call_handler+0xe3/0x100
> [ 63.266655] __vfs_read+0x33/0x1b0
> [ 63.266957] vfs_read+0xa6/0x150
> [ 63.267244] SyS_read+0x55/0xc0
> [ 63.267525] do_syscall_64+0x56/0x140
> [ 63.267850] entry_SYSCALL64_slow_path+0x25/0x25
>
> Fixes: 920d5f77d1a25 ("mm, sysctl: make NUMA stats configurable")
Note that this hash is specific to particular next-$DATE as mmotm is
reimported each day.
> Cc: Jesper Dangaard Brouer <bro...@redhat.com>
> Cc: Dave Hansen <dave.han...@intel.com>
> Cc: Ying Huang <ying.hu...@intel.com>
> Cc: Vlastimil Babka <vba...@suse.cz>
> Cc: Michal Hocko <mho...@suse.com>
> Signed-off-by: Kees Cook <keesc...@chromium.org>
> ---
> mm/vmstat.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index e0593434fd58..40b2db6db6b1 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -72,11 +72,12 @@ static void invalid_numa_statistics(void)
> zero_global_numa_counters();
> }
>
> +static DEFINE_MUTEX(vm_numa_stat_lock);
> +
> int sysctl_vm_numa_stat_handler(struct ctl_table *table, int write,
> void __user *buffer, size_t *length, loff_t *ppos)
> {
> int ret, oldval;
> - DEFINE_MUTEX(vm_numa_stat_lock);
Yeah it was Michal who suggested scoping the mutex here instead of
global scope, but I think he didn't mean to remove the 'static'
qualifier, and we both missed that in the review :(
So the scope under sysctl_vm_numa_stat_handler() should be okay, just
with the 'static' added.
>
> mutex_lock(&vm_numa_stat_lock);
> if (write)
>
