+ mm-fix-mmap-errno-value-when-map_droppable-is-not-supported.patch added to mm-unstable branch

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

The patch titled
     Subject: mm: fix mmap errno value when MAP_DROPPABLE is not supported
has been added to the -mm mm-unstable branch.  Its filename is
     mm-fix-mmap-errno-value-when-map_droppable-is-not-supported.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-mmap-errno-value-when-map_droppable-is-not-supported.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: Anthony Yznaga <anthony.yznaga@oracle.com>
Subject: mm: fix mmap errno value when MAP_DROPPABLE is not supported
Date: Thu, 2 Apr 2026 16:59:32 -0700

Patch series "fix MAP_DROPPABLE not supported errno".

Mark Brown reported seeing a regression in -next on 32 bit arm with the
mlock selftests.  Before exiting and marking the tests failed, the
following message was logged after an attempt to create a MAP_DROPPABLE
mapping:

Bail out! mmap error: Unknown error 524

It turns out error 524 is ENOTSUPP which is an error that userspace is not
supposed to see, but it indicates in this instance that MAP_DROPPABLE is
not supported.

The first patch changes the errno returned to EOPNOTSUPP.  The second
patch is a second version of a prior patch to introduce selftests to
verify locking behavior with droppable mappings with the additonal change
to skip the tests when MAP_DROPPABLE is not supported.


This patch (of 2):

On configs where MAP_DROPPABLE is not supported (currently any 32-bit
config except for PPC32), mmap fails with errno set to ENOTSUPP.  However,
ENOTSUPP is not a standard error value that userspace knows about.  The
acceptable userspace-visible errno to use is EOPNOTSUPP.  checkpatch.pl
has a warning to this effect.

Link: https://lkml.kernel.org/r/20260402235933.10588-1-anthony.yznaga@oracle.com
Link: https://lkml.kernel.org/r/20260402235933.10588-2-anthony.yznaga@oracle.com
Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Acked-by: David Hildenbrand <david@kernel.org>
Reported-by: Mark Brown <broonie@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason A. Donenfeld <jason@zx2c4.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mmap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/mmap.c~mm-fix-mmap-errno-value-when-map_droppable-is-not-supported
+++ a/mm/mmap.c
@@ -504,7 +504,7 @@ unsigned long do_mmap(struct file *file,
 			break;
 		case MAP_DROPPABLE:
 			if (VM_DROPPABLE == VM_NONE)
-				return -ENOTSUPP;
+				return -EOPNOTSUPP;
 			/*
 			 * A locked or stack area makes no sense to be droppable.
 			 *
_

Patches currently in -mm which might be from anthony.yznaga@oracle.com are

mm-fix-mmap-errno-value-when-map_droppable-is-not-supported.patch
selftests-mm-verify-droppable-mappings-cannot-be-locked.patch