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Mon, 28 Apr 2025 08:41:08 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id q+TLOCQ/D2jbBgAAD6G6ig (envelope-from ); Mon, 28 Apr 2025 08:41:08 +0000 Date: Mon, 28 Apr 2025 10:41:03 +0200 From: Oscar Salvador To: Wupeng Ma Cc: akpm@linux-foundation.org, mike.kravetz@oracle.com, david@redhat.com, joshua.hahnjy@gmail.com, muchun.song@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: hugetlb: Fix incorrect fallback for subpool Message-ID: References: <20250410062633.3102457-1-mawupeng1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250410062633.3102457-1-mawupeng1@huawei.com> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 64A12100002 X-Stat-Signature: abbn1ateherq6q8tntitzr8wzhtqggmd X-Rspam-User: X-HE-Tag: 1745829671-214596 X-HE-Meta: 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 R1AHkomJ EHxD+1j9alkHNFG4sL3x7TrsBWv8rUViGLpD9gqcG/tr39yj20sZOJcyCScxAbCUQ1TJ8O+rskEmryH+9a8r67mM2gM2e/Z6tXA9LrFMk/5WowzGxxCqPOCRLMFljgR6GgBT5CcsoTjkLYKSxppvVnzz9IAeLRQQjSXs3GC9si/wEByyrfZmsn0KhSKnPnGcNGDWYsVlDCO1W+SH200SRjie5i9u+ScC7wgT3ZfKA4omzoQIv1pyg8s7Dw72WjBB/tB8wV8oGCZy+2KfPb/GmF7CrCkfjhn9ZsNiNIR2H5oFt7TdFDjX4e7IWcn/EVEXdAk92XkI8ALXf2GoEFQGT3Mq1wbo25wYffUK73io/zolfom+fViwmwRgAXYyev2TFaHFa 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: On Thu, Apr 10, 2025 at 02:26:33PM +0800, Wupeng Ma wrote: > During our testing with hugetlb subpool enabled, we observe that > hstate->resv_huge_pages may underflow into negative values. Root cause > analysis reveals a race condition in subpool reservation fallback handling > as follow: > > hugetlb_reserve_pages() > /* Attempt subpool reservation */ > gbl_reserve = hugepage_subpool_get_pages(spool, chg); > > /* Global reservation may fail after subpool allocation */ > if (hugetlb_acct_memory(h, gbl_reserve) < 0) > goto out_put_pages; > > out_put_pages: > /* This incorrectly restores reservation to subpool */ > hugepage_subpool_put_pages(spool, chg); > > When hugetlb_acct_memory() fails after subpool allocation, the current > implementation over-commits subpool reservations by returning the full > 'chg' value instead of the actual allocated 'gbl_reserve' amount. This > discrepancy propagates to global reservations during subsequent releases, > eventually causing resv_huge_pages underflow. > > This problem can be trigger easily with the following steps: > 1. reverse hugepage for hugeltb allocation > 2. mount hugetlbfs with min_size to enable hugetlb subpool > 3. alloc hugepages with two task(make sure the second will fail due to > insufficient amount of hugepages) > 4. with for a few seconds and repeat step 3 which will make > hstate->resv_huge_pages to go below zero. > > To fix this problem, return corrent amount of pages to subpool during the > fallback after hugepage_subpool_get_pages is called. > > Fixes: 1c5ecae3a93f ("hugetlbfs: add minimum size accounting to subpools") > Signed-off-by: Wupeng Ma > Tested-by: Joshua Hahn Reviewed-by: Oscar Salvador -- Oscar Salvador SUSE Labs