[Intel-gfx] [PATCH 3/3] drm/i915/gem: Mark up the racy read of the mmap_singleton

[Mika Kuoppala]

Chris Wilson <chris at chris-wilson.co.uk> writes:

> [11057.642683] BUG: KCSAN: data-race in i915_gem_mmap [i915] / singleton_release [i915]
> [11057.642717]
> [11057.642740] write (marked) to 0xffff8881f24471a0 of 8 bytes by task 44668 on cpu 2:
> [11057.643162]  singleton_release+0x38/0x60 [i915]
> [11057.643192]  __fput+0x160/0x3c0
> [11057.643217]  ____fput+0x16/0x20
> [11057.643241]  task_work_run+0xba/0x100
> [11057.643263]  exit_to_usermode_loop+0xe4/0xf0
> [11057.643286]  do_syscall_64+0x27e/0x2c0
> [11057.643314]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [11057.643339]
> [11057.643359] read to 0xffff8881f24471a0 of 8 bytes by task 44667 on cpu 3:
> [11057.643774]  i915_gem_mmap+0x295/0x670 [i915]
> [11057.643802]  mmap_region+0x62b/0xac0
> [11057.643825]  do_mmap+0x414/0x6b0
> [11057.643848]  vm_mmap_pgoff+0xa9/0xf0
> [11057.643875]  ksys_mmap_pgoff+0x1ac/0x2f0
> [11057.643900]  do_syscall_64+0x6e/0x2c0
> [11057.643924]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

> ---
>  drivers/gpu/drm/i915/gem/i915_gem_mman.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> index e8cccc131c40..b39c24dae64e 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> @@ -775,7 +775,7 @@ static struct file *mmap_singleton(struct drm_i915_private *i915)
>  	struct file *file;
>  
>  	rcu_read_lock();
> -	file = i915->gem.mmap_singleton;
> +	file = READ_ONCE(i915->gem.mmap_singleton);
>  	if (file && !get_file_rcu(file))
>  		file = NULL;
>  	rcu_read_unlock();
> -- 
> 2.20.1