From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-118.freemail.mail.aliyun.com (out30-118.freemail.mail.aliyun.com [115.124.30.118]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0AFC83AA19B; Mon, 6 Jul 2026 03:25:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.118 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783308335; cv=none; b=K/uPPd1Xe83TwdfoRahNCoXShQw69j4Jhpk0BMqlQDdQ/UF8Uye/1TF9ig1yir20/SvEExStJHTJOplZMDp3Idcl3FauvRDP/AqVb6xREGa20K4OiUBOjMxBKt5C10P40zr1+MmfQrot3o9fnuPekdH6Wo9s41MZKfjHCFr3Uqk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783308335; c=relaxed/simple; bh=lYerO4A/a4J7kBn5242MFojwA3B5A1pKWFOd9bUDyYU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Lb/of3I7r/bbfJweC80l2WPxBXG7zqGLfeMKM02gINsGe6Jf3v5bxgMgzBk5bpZ56v1PfodPa9aBzyULZssr3vRIHrK9yLdeHhklRe3jsAv+MrsMDmKLNtHwqEHoCwEFEAwvcAB/DB8v455DoAQ5zjFHmdJhQleE8rAOY6dGFQM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=c7HajMXj; arc=none smtp.client-ip=115.124.30.118 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="c7HajMXj" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1783308323; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=rfnZ/lC4Rb2GAMPajAZjxcZCPKg4CeTNBMYP2PQYiAY=; b=c7HajMXj9wrMpz+AnAiIM1wf+gK1W9ArW7fsg94AeUKbFSOY9eBqF49ZDNLHw+xFwGKCw+W1Pl1EDelbxLB0h2lDivp9zK3FDFYM1RJlC8U52o/8nST3TuzxdHjchN2iAmFvS8ar4uMmvtuk3TNi2Q19TgohXDgZLe+ctFbFqIg= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R291e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam011083073210;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0X6PRHzq_1783308322; Received: from localhost(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X6PRHzq_1783308322 cluster:ay36) by smtp.aliyun-inc.com; Mon, 06 Jul 2026 11:25:23 +0800 From: Baolin Wang To: akpm@linux-foundation.org, hughd@google.com, stable@vger.kernel.org Cc: kasong@tencent.com, baohua@kernel.org, machao26@xiaomi.com, baolin.wang@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 6.18.y] mm: shmem: fix potential livelock issue for shmem direct swapin Date: Mon, 6 Jul 2026 11:25:13 +0800 Message-ID: <173f3fd983d735155d47e9e39d27f0c2d62a7c31.1783307463.git.baolin.wang@linux.alibaba.com> X-Mailer: git-send-email 2.43.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When skipping swapcache for synchronous IO swap devices, swapcache_prepare() is used to prevent parallel swapin from proceeding with the swap cache flag. However, on PREEMPT kernels this can lead to a livelock, as reported by Chao[1]: Thread A starts direct swapin of a shmem folio and calls swapcache_prepare() to set SWAP_HAS_CACHE. It may then be preempted inside workingset_refault(). Meanwhile, a higher priority thread B also attempts direct swapin of the same shmem swap entry. Since swapcache_prepare() already marks the entry, thread B repeatedly gets -EEXIST and busy-loops waiting for thread A to finish. But as thread B runs at higher priority, thread A cannot preempt it, resulting in starvation and a livelock. Fix it by yielding the CPU with schedule_timeout_uninterruptible(1) when swapcache_prepare() fails, following the same approach used in commits 029c4628b2eb ("mm: swap: get rid of livelock in swapin readahead") and 13ddaf26be32 ("mm/swap: fix race when skipping swapcache"). Note that mainline does not have this potential issue, which has already been resolved by Kairui's swap refactoring work[2]. [1] https://lore.kernel.org/all/700a2cbf90a2484f979aac858f08f5d4@xiaomi.com/ [2] https://lore.kernel.org/all/20260517-swap-table-p4-v5-0-88ae43e064c7@tencent.com/ Fixes: 1dd44c0af4fa ("mm: shmem: skip swapcache for swapin of synchronous swap device") Reported-by: Ma Chao Closes: https://lore.kernel.org/all/700a2cbf90a2484f979aac858f08f5d4@xiaomi.com/ Signed-off-by: Baolin Wang --- Hi Chao, could you try this patch to check if it fixes your issue? Thanks. --- mm/shmem.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 94c5b0d78ac3..d4cb57b3b0ef 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2066,6 +2066,8 @@ static struct folio *shmem_swap_alloc_folio(struct inode *inode, if (swapcache_prepare(entry, nr_pages)) { folio_put(new); new = ERR_PTR(-EEXIST); + /* Relax a bit to prevent rapid repeated page faults */ + schedule_timeout_uninterruptible(1); /* Try smaller folio to avoid cache conflict */ goto fallback; } -- 2.47.3