linux-kernel - [PATCH V3 0/2] mm/khugepaged: fix dirty page handling for MADV

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Message-ID: <20251201185604.210634-6-shivankg@amd.com>
Date: Mon, 1 Dec 2025 18:56:07 +0000
From: Shivank Garg <shivankg@....com>
To: Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand
	<david@...nel.org>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
CC: Zi Yan <ziy@...dia.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, Barry Song
	<baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>, Steven Rostedt
	<rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, "Mathieu
 Desnoyers" <mathieu.desnoyers@...icios.com>, Zach O'Keefe
	<zokeefe@...gle.com>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<linux-trace-kernel@...r.kernel.org>, <shivankg@....com>
Subject: [PATCH V3 0/2] mm/khugepaged: fix dirty page handling for MADV_COLLAPSE

MADV_COLLAPSE on file-backed mappings fails with -EINVAL when TEXT pages
are dirty. This affects scenarios like package/container updates or
executing binaries immediately after writing them, etc.

The issue is that collapse_file() triggers async writeback and returns
SCAN_FAIL (maps to -EINVAL), expecting khugepaged to revisit later. But
MADV_COLLAPSE is synchronous and userspace expects immediate success or
a clear retry signal.

Reproduction:
 - Compile or copy 2MB-aligned executable to XFS/ext4 FS
 - Call MADV_COLLAPSE on .text section
 - First call fails with -EINVAL (text pages dirty from copy)
 - Second call succeeds (async writeback completed)

Issue Report:
https://lore.kernel.org/all/4e26fe5e-7374-467c-a333-9dd48f85d7cc@amd.com

Changelog:
V3:
- Reordered patches: Enum definition comes first as the retry logic depends on it
- Renamed SCAN_PAGE_NOT_CLEAN to SCAN_PAGE_DIRTY_OR_WRITEBACK (Dev, Lance, David)
- Changed writeback logic: Only trigger synchronous writeback and retry if the
  initial collapse attempt failed specifically due to dirty/writeback pages,
  rather than blindly flushing all file-backed VMAs (David)
- Added proper file reference counting (get_file/fput) around the unlock window
  to prevent UAF (Lance)

V2:
- https://lore.kernel.org/all/20251120065043.41738-6-shivankg@amd.com
- Move writeback to madvise_collapse() (better abstraction, proper
  mmap_lock handling and does VMA revalidation after I/O) (Lorenzo)
- Rename to SCAN_PAGE_DIRTY to SCAN_PAGE_NOT_CLEAN and extend its use
  for all dirty/writeback folio cases that previously returned incorrect
  results (Dev) 

V1: https://lore.kernel.org/all/20251110113254.77822-1-shivankg@amd.com

Thanks,

Shivank Garg (2):
  mm/khugepaged: map dirty/writeback pages failures to EAGAIN
  mm/khugepaged: retry with sync writeback for MADV_COLLAPSE

 include/trace/events/huge_memory.h |  3 +-
 mm/khugepaged.c                    | 49 ++++++++++++++++++++++++++++--
 2 files changed, 48 insertions(+), 4 deletions(-)


base-commit: 2178727587e1eaa930b8266377119ed6043067df
-- 
2.43.0