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Fix a few uses of kern_yield() in the TTM and the LinuxKPI.

Browse source 
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
This commit is contained in:
Mark Johnston 2017-05-18 18:35:14 +00:00
parent 3bd485f968
commit 02fb845bbf
2 changed files with 3 additions and 3 deletions
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2
sys/compat/linuxkpi/common/src/linux_compat.c
View file

@ -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);
}
}

4
sys/dev/drm2/ttm/ttm_bo_vm.c
View file

@ -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;