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Date: Wed, 8 Nov 2017 08:43:44 +0100 From: Vlastimil Babka <vbabka@...e.cz> To: Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>, Jesper Dangaard Brouer <brouer@...hat.com> Cc: Dave Hansen <dave.hansen@...el.com>, Ying Huang <ying.huang@...el.com>, Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH] mm, vmstat: Make sure mutex is a global static 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 <brouer@...hat.com> > Cc: Dave Hansen <dave.hansen@...el.com> > Cc: Ying Huang <ying.huang@...el.com> > Cc: Vlastimil Babka <vbabka@...e.cz> > Cc: Michal Hocko <mhocko@...e.com> > Signed-off-by: Kees Cook <keescook@...omium.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) >
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