memory: bail from page scrubbing when CPU is no longer online

Scrubbing can significantly delay the offlining (parking) of a CPU (e.g.
because of booting into in smt=0 mode), to a degree that the "CPU <n>
still not dead..." messages logged on x86 in 1s intervals can be seen
multiple times. There are no softirqs involved in this process, so
extend the existing preemption check in the scrubbing logic to also exit
when the CPU is no longer observed online.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index fcb308d92f97e98e4dba3597db976c972519fc85..02ac1fa613e70dd8c5e6b1d3e9535ac7767b22c7 100644 (file)
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1324,9 +1324,11 @@ bool scrub_free_pages(void)
                      * Scrub a few (8) pages before becoming eligible for
                      * preemption. But also count non-scrubbing loop iterations
                      * so that we don't get stuck here with an almost clean
-                     * heap.
+                     * heap. Consider the CPU no longer being seen as online as
+                     * a request to preempt immediately, to not unduly delay
+                     * its offlining.
                      */
-                    if ( cnt > 800 && softirq_pending(cpu) )
+                    if ( !cpu_online(cpu) || (cnt > 800 && softirq_pending(cpu)) )
                     {
                         preempt = true;
                         break;