From 02fb845bbfb7e5dcfaa8d659c83fa5c9afcae2d3 Mon Sep 17 00:00:00 2001 From: Mark Johnston Date: Thu, 18 May 2017 18:35:14 +0000 Subject: [PATCH] Fix a few uses of kern_yield() in the TTM and the LinuxKPI. kern_yield(0) effectively causes the calling thread to be rescheduled immediately since it resets the thread's priority to the highest possible value. This can cause livelocks when the pattern "while (!trylock()) kern_yield(0);" is used since the thread holding the lock may linger on the runqueue for the CPU on which the looping thread is running. MFC after: 1 week --- sys/compat/linuxkpi/common/src/linux_compat.c | 2 +- sys/dev/drm2/ttm/ttm_bo_vm.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/sys/compat/linuxkpi/common/src/linux_compat.c b/sys/compat/linuxkpi/common/src/linux_compat.c index ecea3a75319..02df4e32518 100644 --- a/sys/compat/linuxkpi/common/src/linux_compat.c +++ b/sys/compat/linuxkpi/common/src/linux_compat.c @@ -435,7 +435,7 @@ linux_cdev_pager_populate(vm_object_t vm_obj, vm_pindex_t pidx, int fault_type, err = vmap->vm_ops->fault(vmap, &vmf); while (vmap->vm_pfn_count == 0 && err == VM_FAULT_NOPAGE) { - kern_yield(0); + kern_yield(PRI_USER); err = vmap->vm_ops->fault(vmap, &vmf); } } diff --git a/sys/dev/drm2/ttm/ttm_bo_vm.c b/sys/dev/drm2/ttm/ttm_bo_vm.c index 60bf8e23c54..6d8bb1129bc 100644 --- a/sys/dev/drm2/ttm/ttm_bo_vm.c +++ b/sys/dev/drm2/ttm/ttm_bo_vm.c @@ -126,7 +126,7 @@ reserve: ret = ttm_bo_reserve(bo, false, false, false, 0); if (unlikely(ret != 0)) { if (ret == -EBUSY) { - kern_yield(0); + kern_yield(PRI_USER); goto reserve; } } @@ -139,7 +139,7 @@ reserve: case -EBUSY: case -ERESTARTSYS: case -EINTR: - kern_yield(0); + kern_yield(PRI_USER); goto reserve; default: retval = VM_PAGER_ERROR;