On Fri, Nov 29, 2019 at 8:33 AM Boris Brezillon boris.brezillon@collabora.com wrote:
On Fri, 29 Nov 2019 14:24:48 +0000 Steven Price steven.price@arm.com wrote:
On 29/11/2019 13:59, Boris Brezillon wrote:
If 2 threads change the MADVISE property of the same BO in parallel we might end up with an shmem->madv value that's inconsistent with the presence of the BO in the shrinker list.
I'm a bit worried from the point of view of user space sanity that you observed this - but clearly the kernel should be robust!
It's not something I observed, just found the race by inspecting the code, and I thought it was worth fixing it.
I'm not so sure there's a race. If there is, we still check madv value when purging, so it would be harmless even if the state is inconsistent.
The easiest solution to fix that is to protect the drm_gem_shmem_madvise() call with the shrinker lock.
Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support") Cc: stable@vger.kernel.org Signed-off-by: Boris Brezillon boris.brezillon@collabora.com
Reviewed-by: Steven Price steven.price@arm.com
Thanks.
drivers/gpu/drm/panfrost/panfrost_drv.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c index f21bc8a7ee3a..efc0a24d1f4c 100644 --- a/drivers/gpu/drm/panfrost/panfrost_drv.c +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c @@ -347,20 +347,19 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data, return -ENOENT; }
- mutex_lock(&pfdev->shrinker_lock); args->retained = drm_gem_shmem_madvise(gem_obj, args->madv);
This means we now hold the shrinker_lock while we take the pages_lock. Is lockdep happy with this change? I suspect not given all the fun I had getting lockdep happy.
Rob