Date: Sun, 25 Aug 2013 15:00:48 +0000 (UTC) From: Jean-Sebastien Pedron <dumbbell@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r254870 - head/sys/dev/drm2/ttm Message-ID: <201308251500.r7PF0mCq053746@svn.freebsd.org>
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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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