Author: dumbbell
Date: Sun Aug 25 15:00:48 2013
New Revision: 254870
URL: http://svnweb.freebsd.org/changeset/base/254870
Log:
drm/ttm: Make ttm_bo_wait() call uninterruptible in page fault handler
This fixes a crash where a SIGLALRM, heavily used by X.Org, would
interrupt the wait, causing the page fault to fail and the "Xorg"
process to receive a SIGSEGV.
Approved by: kib@
Modified:
head/sys/dev/drm2/ttm/ttm_bo_vm.c
Modified: head/sys/dev/drm2/ttm/ttm_bo_vm.c
==============================================================================
--- head/sys/dev/drm2/ttm/ttm_bo_vm.c Sun Aug 25 15:00:34 2013
(r254869)
+++ head/sys/dev/drm2/ttm/ttm_bo_vm.c Sun Aug 25 15:00:48 2013
(r254870)
@@ -154,7 +154,23 @@ reserve:
mtx_lock(&bdev->fence_lock);
if (test_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags)) {
- ret = ttm_bo_wait(bo, false, true, false);
+ /*
+ * Here, the behavior differs between Linux and FreeBSD.
+ *
+ * On Linux, the wait is interruptible (3rd argument to
+ * ttm_bo_wait). There must be some mechanism to resume
+ * page fault handling, once the signal is processed.
+ *
+ * On FreeBSD, the wait is uninteruptible. This is not a
+ * problem as we can't end up with an unkillable process
+ * here, because the wait will eventually time out.
+ *
+ * An example of this situation is the Xorg process
+ * which uses SIGALRM internally. The signal could
+ * interrupt the wait, causing the page fault to fail
+ * and the process to receive SIGSEGV.
+ */
+ ret = ttm_bo_wait(bo, false, false, false);
mtx_unlock(&bdev->fence_lock);
if (unlikely(ret != 0)) {
retval = VM_PAGER_ERROR;
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