From 40313f0cd0b711a7a5905e5182422799e157d8aa Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 5 Apr 2016 15:00:00 +0100 Subject: [PATCH] drm/i915/userptr: Hold mmref whilst calling get-user-pages MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Holding a reference to the containing task_struct is not sufficient to prevent the mm_struct from being reaped under memory pressure. If this happens whilst we are calling get_user_pages(), explosions erupt - sometimes an immediate GPF, sometimes page flag corruption. To prevent the target mm from being reaped as we are reading from it, acquire a reference before we begin. Testcase: igt/gem_shrink/*userptr Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Cc: Michał Winiarski Cc: stable@vger.kernel.org Reviewed-by: Michał Winiarski Link: http://patchwork.freedesktop.org/patch/msgid/1459864801-28606-2-git-send-email-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_gem_userptr.c | 29 +++++++++++++++---------- 1 file changed, 17 insertions(+), 12 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c index d76847e7b636..3e31f59c6203 100644 --- a/drivers/gpu/drm/i915/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c @@ -544,19 +544,24 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work) if (pvec != NULL) { struct mm_struct *mm = obj->userptr.mm->mm; - down_read(&mm->mmap_sem); - while (pinned < npages) { - ret = get_user_pages_remote(work->task, mm, - obj->userptr.ptr + pinned * PAGE_SIZE, - npages - pinned, - !obj->userptr.read_only, 0, - pvec + pinned, NULL); - if (ret < 0) - break; - - pinned += ret; + ret = -EFAULT; + if (atomic_inc_not_zero(&mm->mm_users)) { + down_read(&mm->mmap_sem); + while (pinned < npages) { + ret = get_user_pages_remote + (work->task, mm, + obj->userptr.ptr + pinned * PAGE_SIZE, + npages - pinned, + !obj->userptr.read_only, 0, + pvec + pinned, NULL); + if (ret < 0) + break; + + pinned += ret; + } + up_read(&mm->mmap_sem); + mmput(mm); } - up_read(&mm->mmap_sem); } mutex_lock(&dev->struct_mutex); -- 2.20.1