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Tsirkin" To: linux-kernel@vger.kernel.org Cc: David Hildenbrand , Miaohe Lin , Naoya Horiguchi , Andrew Morton , Oscar Salvador , Andi Kleen , Hidehiro Kawai , Rik van Riel , Vlastimil Babka , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Hao Li , Kiryl Shutsemau , Byungchul Park , linux-mm@kvack.org, linux-cxl@vger.kernel.org, David Hildenbrand Subject: [PATCH 0/2] mm: memory-failure: fix HWPoison flag race with non-atomic page flag ops Message-ID: MIME-Version: 1.0 X-Mailer: git-send-email 2.51.2.2891.g4157995a80.dirty X-Mutt-Fcc: =sent X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: vjT9DcIowDW2OITX-XgXBbpdSz7DKNMXaQPKQv7TuFs_1782683128 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 07F3A20009 X-Rspam-User: X-Stat-Signature: 1cw4b57p964gft3zre1ogtxb3j6a7gfu X-HE-Tag: 1782683131-744152 X-HE-Meta: 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 wXF47uui FgsUEFYKQB2mlr0umM2RzBxz8c22aXhpUCjkhFt9vg6qZjwg7JzAAJfE78/1BYcgXJXjmgm+F0YCGvNQHXfRsNApsd5PU6yovvuFBKqJmFXTZAYdb1ip3758XjGiJTlHtuJg1l4NF3+Bmg6ZYNiYUw95kfPK6ad3WWV9wX9VYduF1DoLNXCvnWjiY1I7vN7mQqv/Cb1dTQA+8sVnlQbq5brpiChl3rcPZrFRNQQOm6h0JaGMiZSg0xkh8uRYEgwDlxixqfE8p6AM3MaMKmilqUSlmEs2LMRvKuC+5n75mFsEayiMyrNaQyugzL0RiUi9pjai47La8+hHTJv6Oio4QIosmF2qnSC6Daa3J3Cb7iU427giLq/3tGtmC/oMkNrcQUen+WWZ1jm8e/Kush6PispP30Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: I don't like it that we are adding overhead to the good path for the benefit of memory failure, which never triggers on many systems, but I don't have a better idea. Pls take a look. Non-atomic page flag operations (page->flags.f &= ~mask, __set_bit, __clear_bit) can race with atomic TestSetPageHWPoison() in memory_failure(). The non-atomic RMW reads flags, memory_failure() atomically sets HWPoison, then the RMW writes back the old value without HWPoison, clobbering the bit. The race was confirmed by injecting a cpu_relax() delay between the load and store of the non-atomic RMW in __free_pages_prepare, then running concurrent MADV_HWPOISON injection. The clobbered HWPoison bit was observed repeatedly. This series fixes the race by: 1. Having memory_failure() call synchronize_rcu() + retry after setting HWPoison, so that any in-flight non-atomic RMW that read the old flags value completes before we proceed. 2. Wrapping all non-atomic page flag operations in rcu_read_lock/rcu_read_unlock (CONFIG_MEMORY_FAILURE only), so that synchronize_rcu() actually drains them. Performance impact (page alloc+free microbenchmark, 200K iterations, 20 runs, KVM guest, error bars are 3-sigma): !PREEMPT_RCU (x86): insns/iter cycles/iter base: 12237 +/- 1 17954 +/- 136 patched: +22 +/- 1 -124 +/- 122 (+0.18%) (within noise) PREEMPT_RCU: insns/iter cycles/iter base: 12512 +/- 3 18541 +/- 214 patched: +95 +/- 3 -12 +/- 161 (+0.76%) (within noise) When !CONFIG_MEMORY_FAILURE, all wrappers compile away completely. Suggested-by: David Hildenbrand Michael S. Tsirkin (2): mm: memory-failure: use RCU to fix HWPoison flag race mm: wrap non-atomic page flag ops in RCU for HWPoison safety include/linux/mm.h | 7 ++++ include/linux/page-flags.h | 81 +++++++++++++++++++++++++++++++++++--- mm/huge_memory.c | 2 + mm/memory-failure.c | 54 +++++++++++++++++++++---- mm/memremap.c | 6 ++- mm/mm_init.c | 2 + mm/page_alloc.c | 4 ++ mm/slub.c | 2 +- 8 files changed, 143 insertions(+), 15 deletions(-) -- MST