+ hugetlbfs-move-hugetlbfs_free_inode-tracepoint-to-destroy_inode.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: hugetlbfs: move hugetlbfs_free_inode tracepoint to ->destroy_inode()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     hugetlbfs-move-hugetlbfs_free_inode-tracepoint-to-destroy_inode.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hugetlbfs-move-hugetlbfs_free_inode-tracepoint-to-destroy_inode.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Joas Antonio dos Santos <joasantonio108@gmail.com>
Subject: hugetlbfs: move hugetlbfs_free_inode tracepoint to ->destroy_inode()
Date: Sun, 01 Nov 2026 13:48:55 +0000

hugetlbfs_free_inode() calls trace_hugetlbfs_free_inode(), and the
hugetlbfs__inode event class records inode->i_sb->s_dev.  ->free_inode()
runs from an RCU callback (destroy_inode() queues i_callback() with
call_rcu()), and Documentation/filesystems/porting.rst says that this
callback "is *NOT* ordered wrt superblock destruction; as the matter of
fact, the superblock and all associated structures might be already gone".
put_super() frees the superblock with call_rcu() followed by a workqueue
item (destroy_super_rcu() -> destroy_super_work()).  syzbot hit this with
the event enabled:

  BUG: KASAN: slab-use-after-free in trace_event_raw_event_hugetlbfs__inode+0x45b/0x4c0 include/trace/events/hugetlbfs.h:36
  Read of size 4 at addr ffff888038850010 by task syz-executor952/6134
   hugetlbfs_free_inode+0x15e/0x1f0 fs/hugetlbfs/inode.c:1182
   i_callback+0x46/0x80 fs/inode.c:317
   rcu_do_batch kernel/rcu/tree.c:2650 [inline]
   rcu_core+0x5f0/0x1220 kernel/rcu/tree.c:2919
  Allocated by task 6134:
   alloc_super fs/super.c:326 [inline]
   sget_fc+0x1ba/0x1f60 fs/super.c:874
   hugetlbfs_get_tree+0x1e7/0x2b0 fs/hugetlbfs/inode.c:1431
  Freed by task 855:
   kfree+0x22b/0x6d0 mm/slub.c:6923
   process_one_work+0xac7/0x1b10 kernel/workqueue.c:3495

Emit the event from hugetlbfs_destroy_inode() instead.  destroy_inode()
calls ->destroy_inode() synchronously, before it queues the RCU callback,
while the superblock is still alive; hugetlbfs_destroy_inode() already
dereferences inode->i_sb there.  ->free_inode() is left with only the
kmem_cache_free().

Since the event no longer fires from ->free_inode(), rename it to
hugetlbfs_destroy_inode so that its name matches where it is emitted, as
suggested by David and Muchun.

Found by syzbot; analysed and tested with the syzbot C reproducer on an
arm64 KASAN kernel.

Link: https://lore.kernel.org/20261101-b4-hugetlbfs-trace-v3-1-051b716f490f@gmail.com
Fixes: 014ad7c42a69 ("hugetlbfs: use tracepoints in hugetlbfs functions.")
Signed-off-by: Joas Antonio dos Santos <joasantonio108@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: <syzbot+91e1fc35f51774c479b2@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/6ae27525.5451848c.f7707.0001.GAE@google.com/
Suggested-by: David Hildenbrand <david@kernel.org>
Suggested-by: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Hongbo Li <lihongbo22@huawei.com>
Cc: <stable@vger.kernel.org>
---

 fs/hugetlbfs/inode.c             |    6 +++++-
 include/trace/events/hugetlbfs.h |    2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

--- a/fs/hugetlbfs/inode.c~hugetlbfs-move-hugetlbfs_free_inode-tracepoint-to-destroy_inode
+++ a/fs/hugetlbfs/inode.c
@@ -1179,12 +1179,16 @@ static struct inode *hugetlbfs_alloc_ino
 
 static void hugetlbfs_free_inode(struct inode *inode)
 {
-	trace_hugetlbfs_free_inode(inode);
 	kmem_cache_free(hugetlbfs_inode_cachep, HUGETLBFS_I(inode));
 }
 
 static void hugetlbfs_destroy_inode(struct inode *inode)
 {
+	/*
+	 * Not in ->free_inode(): that runs from an RCU callback, when the
+	 * superblock the event reads may already be freed.
+	 */
+	trace_hugetlbfs_destroy_inode(inode);
 	hugetlbfs_inc_free_inodes(HUGETLBFS_SB(inode->i_sb));
 }
 
--- a/include/trace/events/hugetlbfs.h~hugetlbfs-move-hugetlbfs_free_inode-tracepoint-to-destroy_inode
+++ a/include/trace/events/hugetlbfs.h
@@ -72,7 +72,7 @@ DEFINE_EVENT(hugetlbfs__inode, hugetlbfs
 	TP_ARGS(inode)
 );
 
-DEFINE_EVENT(hugetlbfs__inode, hugetlbfs_free_inode,
+DEFINE_EVENT(hugetlbfs__inode, hugetlbfs_destroy_inode,
 
 	TP_PROTO(struct inode *inode),
 
_

Patches currently in -mm which might be from joasantonio108@gmail.com are

hugetlbfs-move-hugetlbfs_free_inode-tracepoint-to-destroy_inode.patch