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hugetlb: simplify prep_compound_gigantic_page ref count racing code 

Code in prep_compound_gigantic_page waits for a rcu grace period if it
notices a temporarily inflated ref count on a tail page.  This was due to
the identified potential race with speculative page cache references which
could only last for a rcu grace period.  This is overly complicated as
this situation is VERY unlikely to ever happen.  Instead, just quickly
return an error.

Also, only print a warning in prep_compound_gigantic_page instead of
multiple callers.

Link: https://lkml.kernel.org/r/20210809184832.18342-2-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mike Kravetz 2021-09-02 14:58:43 -07:00 committed by Linus Torvalds
parent f87060d345
commit 416d85ed3e
1 changed files with 7 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
mm/hugetlb.c
View File

@ -1657,16 +1657,14 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order)
* cache adding could take a ref on a 'to be' tail page.
* We need to respect any increased ref count, and only set
* the ref count to zero if count is currently 1. If count
* is not 1, we call synchronize_rcu in the hope that a rcu
* grace period will cause ref count to drop and then retry.
* If count is still inflated on retry we return an error and
* must discard the pages.
* is not 1, we return an error. An error return indicates
* the set of pages can not be converted to a gigantic page.
* The caller who allocated the pages should then discard the
* pages using the appropriate free interface.
*/
if (!page_ref_freeze(p, 1)) {
pr_info("HugeTLB unexpected inflated ref count on freshly allocated page\n");
synchronize_rcu();
if (!page_ref_freeze(p, 1))
goto out_error;
pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");
goto out_error;
}
set_page_count(p, 0);
set_compound_head(p, page);
@ -1830,7 +1828,6 @@ retry:
retry = true;
goto retry;
}
pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");
return NULL;
}
}
@ -2828,8 +2825,8 @@ static void __init gather_bootmem_prealloc(void)
prep_new_huge_page(h, page, page_to_nid(page));
put_page(page); /* add to the hugepage allocator */
} else {
/* VERY unlikely inflated ref count on a tail page */
free_gigantic_page(page, huge_page_order(h));
pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");
}
/*