[xen master] xen/page_alloc: Don't hold the heap_lock when clearing PGC_need_scrub

[patchbot@xxxxxxx]

commit 025eacc13f6147ffa99da5ecee4ed96e7fe8e887
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Thu Jan 21 11:12:00 2021 +0000
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Wed Apr 7 19:30:55 2021 +0100

    xen/page_alloc: Don't hold the heap_lock when clearing PGC_need_scrub
    
    Currently, the heap_lock is held when clearing PGC_need_scrub in
    alloc_heap_pages(). However, this is unnecessary because the only caller
    (mark_page_offline()) that can concurrently modify the count_info is
    using cmpxchg() in a loop.
    
    Therefore, rework the code to avoid holding the heap_lock and use
    test_and_clear_bit() instead.
    
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/page_alloc.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 1744e6faa5..ace6333c18 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1032,16 +1032,12 @@ static struct page_info *alloc_heap_pages(
     {
         for ( i = 0; i < (1U << order); i++ )
         {
-            if ( test_bit(_PGC_need_scrub, &pg[i].count_info) )
+            if ( test_and_clear_bit(_PGC_need_scrub, &pg[i].count_info) )
             {
                 if ( !(memflags & MEMF_no_scrub) )
                     scrub_one_page(&pg[i]);
 
                 dirty_cnt++;
-
-                spin_lock(&heap_lock);
-                pg[i].count_info &= ~PGC_need_scrub;
-                spin_unlock(&heap_lock);
             }
             else if ( !(memflags & MEMF_no_scrub) )
                 check_one_page(&pg[i]);
--
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