FAILED: patch "[PATCH] mm/hugetlb: fix folio is still mapped when deleted" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 7b7387650dcf2881fd8bb55bcf3c8bd6c9542dd7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025092930-header-irritable-c8ed@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7b7387650dcf2881fd8bb55bcf3c8bd6c9542dd7 Mon Sep 17 00:00:00 2001
From: Jinjiang Tu <[email protected]>
Date: Fri, 12 Sep 2025 15:41:39 +0800
Subject: [PATCH] mm/hugetlb: fix folio is still mapped when deleted

Migration may be raced with fallocating hole. remove_inode_single_folio will unmap the folio if the folio is still mapped. However, it's called without folio lock. If the folio is migrated and the mapped pte has been converted to migration entry, folio_mapped() returns false, and won't unmap it. Due to extra refcount held by remove_inode_single_folio, migration fails, restores migration entry to normal pte, and the folio is mapped again. As a result, we triggered BUG in filemap_unaccount_folio.

The log is as follows:

 BUG: Bad page cache in process hugetlb  pfn:156c00
 page: refcount:515 mapcount:0 mapping:0000000099fef6e1 index:0x0 pfn:0x156c00
 head: order:9 mapcount:1 entire_mapcount:1 nr_pages_mapped:0 pincount:0
 aops:hugetlbfs_aops ino:dcc dentry name(?):"my_hugepage_file"
 flags: 0x17ffffc00000c1(locked|waiters|head|node=0|zone=2|lastcpupid=0x1fffff)
 page_type: f4(hugetlb)
 page dumped because: still mapped when deleted
 CPU: 1 UID: 0 PID: 395 Comm: hugetlb Not tainted 6.17.0-rc5-00044-g7aac71907bde-dirty #484 NONE
 Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
 Call Trace:
  <TASK>
  dump_stack_lvl+0x4f/0x70
  filemap_unaccount_folio+0xc4/0x1c0
  __filemap_remove_folio+0x38/0x1c0
  filemap_remove_folio+0x41/0xd0
  remove_inode_hugepages+0x142/0x250
  hugetlbfs_fallocate+0x471/0x5a0
  vfs_fallocate+0x149/0x380

Hold folio lock before checking if the folio is mapped to avold race with migration.

index 09d4baef29cf..be4be99304bc 100644
@@ -517,14 +517,16 @@ static bool remove_inode_single_folio(struct hstate *h, struct inode *inode,
 
 	/*
 	 * If folio is mapped, it was faulted in after being
-	 * unmapped in caller.  Unmap (again) while holding
-	 * the fault mutex.  The mutex will prevent faults
-	 * until we finish removing the folio.
+	 * unmapped in caller or hugetlb_vmdelete_list() skips
+	 * unmapping it due to fail to grab lock.  Unmap (again)
+	 * while holding the fault mutex.  The mutex will prevent
+	 * faults until we finish removing the folio.  Hold folio
+	 * lock to guarantee no concurrent migration.
 	 */
+	folio_lock(folio);
 	if (unlikely(folio_mapped(folio)))
 		hugetlb_unmap_file_folio(h, mapping, folio, index);
 
-	folio_lock(folio);
 	/*
 	 * We must remove the folio from page cache before removing
 	 * the region/ reserve map (hugetlb_unreserve_pages).  In

From: Jinjiang Tu <[email protected]>

[ Upstream commit 7b7387650dcf2881fd8bb55bcf3c8bd6c9542dd7 ]

Migration may be raced with fallocating hole. remove_inode_single_folio will unmap the folio if the folio is still mapped. However, it's called without folio lock. If the folio is migrated and the mapped pte has been converted to migration entry, folio_mapped() returns false, and won't unmap it. Due to extra refcount held by remove_inode_single_folio, migration fails, restores migration entry to normal pte, and the folio is mapped again. As a result, we triggered BUG in filemap_unaccount_folio.

The log is as follows:

 BUG: Bad page cache in process hugetlb  pfn:156c00
 page: refcount:515 mapcount:0 mapping:0000000099fef6e1 index:0x0 pfn:0x156c00
 head: order:9 mapcount:1 entire_mapcount:1 nr_pages_mapped:0 pincount:0
 aops:hugetlbfs_aops ino:dcc dentry name(?):"my_hugepage_file"
 flags: 0x17ffffc00000c1(locked|waiters|head|node=0|zone=2|lastcpupid=0x1fffff)
 page_type: f4(hugetlb)
 page dumped because: still mapped when deleted
 CPU: 1 UID: 0 PID: 395 Comm: hugetlb Not tainted 6.17.0-rc5-00044-g7aac71907bde-dirty #484 NONE
 Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
 Call Trace:
  <TASK>
  dump_stack_lvl+0x4f/0x70
  filemap_unaccount_folio+0xc4/0x1c0
  __filemap_remove_folio+0x38/0x1c0
  filemap_remove_folio+0x41/0xd0
  remove_inode_hugepages+0x142/0x250
  hugetlbfs_fallocate+0x471/0x5a0
  vfs_fallocate+0x149/0x380

Hold folio lock before checking if the folio is mapped to avold race with migration.

---
 fs/hugetlbfs/inode.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

index c8a5d94561ff2..3105376741865 100644
@@ -519,13 +519,13 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 
 			/*
 			 * If page is mapped, it was faulted in after being
-			 * unmapped in caller.  Unmap (again) now after taking
-			 * the fault mutex.  The mutex will prevent faults
-			 * until we finish removing the page.
-			 *
-			 * This race can only happen in the hole punch case.
-			 * Getting here in a truncate operation is a bug.
+			 * unmapped in caller or hugetlb_vmdelete_list() skips
+			 * unmapping it due to fail to grab lock.  Unmap (again)
+			 * while holding the fault mutex.  The mutex will prevent
+			 * faults until we finish removing the page.  Hold page
+			 * lock to guarantee no concurrent migration.
 			 */
+			lock_page(page);
 			if (unlikely(page_mapped(page))) {
 				BUG_ON(truncate_op);
 

@@ -537,8 +537,6 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 					(index + 1) * pages_per_huge_page(h));
 				i_mmap_unlock_write(mapping);
 			}
-
-			lock_page(page);
 			/*
 			 * We must free the huge page and remove from page
 			 * cache (remove_huge_page) BEFORE removing the

2.51.0