+ mm-fix-vma_start_write_killable-signal-handling.patch added to mm-unstable branch

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

The patch titled
     Subject: mm: fix vma_start_write_killable() signal handling
has been added to the -mm mm-unstable branch.  Its filename is
     mm-fix-vma_start_write_killable-signal-handling.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-vma_start_write_killable-signal-handling.patch

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

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------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: mm: fix vma_start_write_killable() signal handling
Date: Fri, 28 Nov 2025 04:00:58 +0000

If we get a signal, we need to restore the vm_refcnt.  We don't think that
the refcount can actually be decremented to zero here as it requires the
VMA to be detached, and the vma_mark_detached() uses TASK_UNINTERRUPTIBLE.
However, that's a bit subtle, so handle it as if the refcount was zero at
the start of this function.

Link: https://lkml.kernel.org/r/20251128040100.3022561-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Reported-by: syzbot+5b19bad23ac7f44bf8b8@syzkaller.appspotmail.com
Fixes: 2197bb60f890 ("mm: add vma_start_write_killable()")
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mmap_lock.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/mm/mmap_lock.c~mm-fix-vma_start_write_killable-signal-handling
+++ a/mm/mmap_lock.c
@@ -74,6 +74,14 @@ static inline int __vma_enter_locked(str
 		   refcount_read(&vma->vm_refcnt) == tgt_refcnt,
 		   state);
 	if (err) {
+		if (refcount_sub_and_test(VMA_LOCK_OFFSET, &vma->vm_refcnt)) {
+			/*
+			 * The wait failed, but the last reader went away
+			 * as well.  Tell the caller the VMA is detached.
+			 */
+			WARN_ON_ONCE(!detaching);
+			err = 0;
+		}
 		rwsem_release(&vma->vmlock_dep_map, _RET_IP_);
 		return err;
 	}
_

Patches currently in -mm which might be from willy@infradead.org are

mm-fix-vma_start_write_killable-signal-handling.patch