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Tue, 20 Jan 2026 09:11:15 +0800 (CST) Received: from kwepemr500001.china.huawei.com (unknown [7.202.194.229]) by mail.maildlp.com (Postfix) with ESMTPS id 1709540539; Tue, 20 Jan 2026 09:14:38 +0800 (CST) Received: from huawei.com (10.50.85.135) by kwepemr500001.china.huawei.com (7.202.194.229) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Tue, 20 Jan 2026 09:14:37 +0800 From: Jinjiang Tu To: , , , , , , , , , , , CC: , Subject: [PATCH v4] mm/mempolicy: fix mpol_rebind_nodemask() for MPOL_F_NUMA_BALANCING Date: Tue, 20 Jan 2026 09:10:18 +0800 Message-ID: <20260120011018.1256654-1-tujinjiang@huawei.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.50.85.135] X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To kwepemr500001.china.huawei.com (7.202.194.229) X-Stat-Signature: pn9ebagbtjdt5xmcqggh4318xx6gai1r X-Rspamd-Queue-Id: AFA011A0004 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1768871683-757003 X-HE-Meta: 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 IZL50EgG G5w+DajUHu1mMgPLFfBItYFBPk+872M97gxNtbgoyHmVcxtCBdU9tGY8pWGQflx3GYKst95LN9l5G+RQPBK8zCvF0WuUKYqD88LMVzQ6P6jOtN2LZ8cgdfwJk++05N7doOComW5lUKLTo6G3tMPibEHjbbUb7vSC6xyUv94RnNb9KZ4fYFYO4wXb1onEZm5Lj3KrEZorKwCZ/DadyY2FQwFTvoPSETbieVAjSpNS32U6FCPvcGmAzV/G1MBojsUcuB/b0qPycmojaMPYSlXzeQwJm0q6yNMPZvdQaHsG1uwWPUAoknEiNw6YYs9nWHj0QMCN4Js2m0qq+qxcK0yP4fgNO+WcW3f4knyaXNoiaseAnHjd7+XOCjS7EwjY+y3/8E9f26L4GI6sFkqsaLxHLQSCLT2c8zEFDXwbnPK0QP8AqhV80aWaCKosKHozjHKkFNq/TseLELsFJ/cZ6DO/g5XdaKZA2KpBvKAYmwJwFOnbLNy1z3PdQh6or23gN0q/duXFhxN+qWSanKuY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: commit bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes") adds new flag MPOL_F_NUMA_BALANCING to enable NUMA balancing for MPOL_BIND memory policy. When the cpuset of tasks changes, the mempolicy of the task is rebound by mpol_rebind_nodemask(). When MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES are both not set, the behaviour of rebinding should be same whenever MPOL_F_NUMA_BALANCING is set or not. So, when an application calls set_mempolicy() with MPOL_F_NUMA_BALANCING set but both MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES cleared, mempolicy.w.cpuset_mems_allowed should be set to cpuset_current_mems_allowed nodemask. However, in current implementation, mpol_store_user_nodemask() wrongly returns true, causing mempolicy->w.user_nodemask to be incorrectly set to the user-specified nodemask. Later, when the cpuset of the application changes, mpol_rebind_nodemask() ends up rebinding based on the user-specified nodemask rather than the cpuset_mems_allowed nodemask as intended. I can reproduce with the following steps in qemu with 4 NUMA nodes: 1. echo '+cpuset' > /sys/fs/cgroup/cgroup.subtree_control 2. mkdir /sys/fs/cgroup/test 3. ./reproducer & 4. cat /proc/$pid/numa_maps, the task is bound to NUMA 1 5. echo $pid > /sys/fs/cgroup/test/cgroup.procs 6. cat /proc/$pid/numa_maps, the task is bound to NUMA 0 now. The reproducer code: int main() { struct bitmask *bmp; int ret; bmp = numa_parse_nodestring("1"); ret = set_mempolicy(MPOL_BIND | MPOL_F_NUMA_BALANCING, bmp->maskp, bmp->size + 1); if (ret < 0) { perror("Failed to call set_mempolicy"); exit(-1); } while (1); return 0; } If I call set_mempolicy() without MPOL_F_NUMA_BALANCING in the reproducer code. After step 5, the task is still bound to NUMA 1. To fix this, only set mempolicy->w.user_nodemask to the user-specified nodemask if MPOL_F_STATIC_NODES or MPOL_F_RELATIVE_NODES is present. Fixes: bda420b98505 ("numa balancing: migrate on fault among multiple bound nodes") Reviewed-by: Gregory Price Reviewed-by: Huang Ying Acked-by: David Hildenbrand (Red Hat) Signed-off-by: Jinjiang Tu --- Change in v4: * add reproducer into changelog * collect Acked-by from David include/uapi/linux/mempolicy.h | 3 +++ mm/mempolicy.c | 2 +- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/mempolicy.h b/include/uapi/linux/mempolicy.h index 8fbbe613611a..6c962d866e86 100644 --- a/include/uapi/linux/mempolicy.h +++ b/include/uapi/linux/mempolicy.h @@ -39,6 +39,9 @@ enum { #define MPOL_MODE_FLAGS \ (MPOL_F_STATIC_NODES | MPOL_F_RELATIVE_NODES | MPOL_F_NUMA_BALANCING) +/* Whether the nodemask is specified by users */ +#define MPOL_USER_NODEMASK_FLAGS (MPOL_F_STATIC_NODES | MPOL_F_RELATIVE_NODES) + /* Flags for get_mempolicy */ #define MPOL_F_NODE (1<<0) /* return next IL mode instead of node mask */ #define MPOL_F_ADDR (1<<1) /* look up vma using address */ diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 68a98ba57882..76da50425712 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -365,7 +365,7 @@ static const struct mempolicy_operations { static inline int mpol_store_user_nodemask(const struct mempolicy *pol) { - return pol->flags & MPOL_MODE_FLAGS; + return pol->flags & MPOL_USER_NODEMASK_FLAGS; } static void mpol_relative_nodemask(nodemask_t *ret, const nodemask_t *orig, -- 2.43.0