From: Chris Wilson Date: Tue, 5 Apr 2016 14:00:00 +0000 (+0100) Subject: drm/i915/userptr: Hold mmref whilst calling get-user-pages X-Git-Tag: v3.16.36~83 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=646178dc82215c0314d7da4c7b60defdc9a9199a;p=thirdparty%2Fkernel%2Fstable.git drm/i915/userptr: Hold mmref whilst calling get-user-pages commit db9f9203e27495b2d151b695504e286eec026e9b upstream. 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 Reviewed-by: Michał Winiarski Link: http://patchwork.freedesktop.org/patch/msgid/1459864801-28606-2-git-send-email-chris@chris-wilson.co.uk (cherry picked from commit 40313f0cd0b711a7a5905e5182422799e157d8aa) Signed-off-by: Jani Nikula [bwh: Backported to 3.16: - s/get_user_pages_remote/get_user_pages/ - s/npages/num_pages/] Signed-off-by: Ben Hutchings --- diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c index 3d98e0d2903d8..3ac65a3c71246 100644 --- a/drivers/gpu/drm/i915/i915_gem_userptr.c +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c @@ -411,19 +411,24 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work) if (pvec != NULL) { struct mm_struct *mm = obj->userptr.mm; - down_read(&mm->mmap_sem); - while (pinned < num_pages) { - ret = get_user_pages(work->task, mm, - obj->userptr.ptr + pinned * PAGE_SIZE, - num_pages - 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 < num_pages) { + ret = get_user_pages + (work->task, mm, + obj->userptr.ptr + pinned * PAGE_SIZE, + num_pages - 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);