linux-kernel - [PATCH] Revert "mm: Always release pages to the buddy allocator in memblock_free

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Message-Id: <20230207082151.1303-1-dev@aaront.org>
Date:   Tue,  7 Feb 2023 08:21:51 +0000
From:   Aaron Thompson <dev@...ont.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Aaron Thompson <dev@...ont.org>
Subject: [PATCH] Revert "mm: Always release pages to the buddy allocator in memblock_free_late()."

This reverts commit 115d9d77bb0f9152c60b6e8646369fa7f6167593.

The pages being freed by memblock_free_late() have already been
initialized, but if they are in the deferred init range,
__free_one_page() might access nearby uninitialized pages when trying to
coalesce buddies. This can, for example, trigger this BUG:

  BUG: unable to handle page fault for address: ffffe964c02580c8
  RIP: 0010:__list_del_entry_valid+0x3f/0x70
   <TASK>
   __free_one_page+0x139/0x410
   __free_pages_ok+0x21d/0x450
   memblock_free_late+0x8c/0xb9
   efi_free_boot_services+0x16b/0x25c
   efi_enter_virtual_mode+0x403/0x446
   start_kernel+0x678/0x714
   secondary_startup_64_no_verify+0xd2/0xdb
   </TASK>

A proper fix will be more involved so revert this change for the time
being.

Fixes: 115d9d77bb0f ("mm: Always release pages to the buddy allocator in memblock_free_late().")
Signed-off-by: Aaron Thompson <dev@...ont.org>
---
 mm/memblock.c                     | 8 +-------
 tools/testing/memblock/internal.h | 4 ----
 2 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 685e30e6d27c..d036c7861310 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1640,13 +1640,7 @@ void __init memblock_free_late(phys_addr_t base, phys_addr_t size)
 	end = PFN_DOWN(base + size);
 
 	for (; cursor < end; cursor++) {
-		/*
-		 * Reserved pages are always initialized by the end of
-		 * memblock_free_all() (by memmap_init() and, if deferred
-		 * initialization is enabled, memmap_init_reserved_pages()), so
-		 * these pages can be released directly to the buddy allocator.
-		 */
-		__free_pages_core(pfn_to_page(cursor), 0);
+		memblock_free_pages(pfn_to_page(cursor), cursor, 0);
 		totalram_pages_inc();
 	}
 }
diff --git a/tools/testing/memblock/internal.h b/tools/testing/memblock/internal.h
index 85973e55489e..fdb7f5db7308 100644
--- a/tools/testing/memblock/internal.h
+++ b/tools/testing/memblock/internal.h
@@ -15,10 +15,6 @@ bool mirrored_kernelcore = false;
 
 struct page {};
 
-void __free_pages_core(struct page *page, unsigned int order)
-{
-}
-
 void memblock_free_pages(struct page *page, unsigned long pfn,
 			 unsigned int order)
 {
-- 
2.30.2