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Commit fc36def9 authored by Pavel Tatashin's avatar Pavel Tatashin Committed by Linus Torvalds
Browse files

mm: teach dump_page() to correctly output poisoned struct pages 

If struct page is poisoned, and uninitialized access is detected via
PF_POISONED_CHECK(page) dump_page() is called to output the page.  But,
the dump_page() itself accesses struct page to determine how to print
it, and therefore gets into a recursive loop.

For example:

  dump_page()
   __dump_page()
    PageSlab(page)
     PF_POISONED_CHECK(page)
      VM_BUG_ON_PGFLAGS(PagePoisoned(page), page)
       dump_page() recursion loop.

Link: http://lkml.kernel.org/r/20180702180536.2552-1-pasha.tatashin@oracle.com


Fixes: f165b378 ("mm: uninitialized struct page poisoning sanity checking")
Signed-off-by: default avatarPavel Tatashin <pasha.tatashin@oracle.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5e4e290d

mm/debug.c

+16 −2
Original line number Diff line number Diff line
@@ -43,12 +43,25 @@ const struct trace_print_flags vmaflag_names[] = { 


void __dump_page(struct page *page, const char *reason)

{

	bool page_poisoned = PagePoisoned(page);

	int mapcount;



	/*

	 * If struct page is poisoned don't access Page*() functions as that

	 * leads to recursive loop. Page*() check for poisoned pages, and calls

	 * dump_page() when detected.

	 */

	if (page_poisoned) {

		pr_emerg("page:%px is uninitialized and poisoned", page);

		goto hex_only;

	}



	/*

	 * Avoid VM_BUG_ON() in page_mapcount().

	 * page->_mapcount space in struct page is used by sl[aou]b pages to

	 * encode own info.

	 */

	int mapcount = PageSlab(page) ? 0 : page_mapcount(page);

	mapcount = PageSlab(page) ? 0 : page_mapcount(page);



	pr_emerg("page:%px count:%d mapcount:%d mapping:%px index:%#lx",

		  page, page_ref_count(page), mapcount,
@@ -60,6 +73,7 @@ void __dump_page(struct page *page, const char *reason) 


	pr_emerg("flags: %#lx(%pGp)\n", page->flags, &page->flags);



hex_only:

	print_hex_dump(KERN_ALERT, "raw: ", DUMP_PREFIX_NONE, 32,

			sizeof(unsigned long), page,

			sizeof(struct page), false);
@@ -68,7 +82,7 @@ void __dump_page(struct page *page, const char *reason) 
		pr_alert("page dumped because: %s\n", reason);



#ifdef CONFIG_MEMCG

	if (page->mem_cgroup)

	if (!page_poisoned && page->mem_cgroup)

		pr_alert("page->mem_cgroup:%px\n", page->mem_cgroup);

#endif

}