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Wed, 17 Sep 2025 08:18:49 +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 tmJsAeluymhZBAAAD6G6ig (envelope-from ); Wed, 17 Sep 2025 08:18:49 +0000 Date: Wed, 17 Sep 2025 10:18:47 +0200 From: Oscar Salvador To: Jane Chu Cc: david@redhat.com, harry.yoo@oracle.com, liushixin2@huawei.com, muchun.song@linux.dev, akpm@linux-foundation.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 RESEND] mm/hugetlb: fix copy_hugetlb_page_range() to use ->pt_share_count Message-ID: References: <20250916191252.1653993-1-jane.chu@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250916191252.1653993-1-jane.chu@oracle.com> X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 988DA140006 X-Stat-Signature: 41q5mse6mx415d6gc19xo3gya71153z5 X-HE-Tag: 1758097131-713283 X-HE-Meta: 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 TCB+WeQn QL4XLEvvI493pkTgXMBibASUi6zlu2MRY893HYNwgL9z9ck+7w1UjPIZTKS6+3zUXX1ifgXCWEzjHtEDF2UDQ6S5apo/6oEo0LsTxMfpoIsV8fDAsy6ZoMRZaS5kqhAuQz3lgGvFaRg2tiZE979r5/747YAgy+nCLY6+bWvmYZcwltqg6Wr+UFWLmw895BImrwJSvTESDVDI2d5duaToUPKvXkf/cvudvkYGwfuxvU/x3W6pUyANT2K3uQ1u4x+4l6LrheJFFTl2cazswzHehgm5tVGd+Hdfvmol5aRDJF5usdLenOBG8P2yNvtUSD+cT9bxLdTAJZeeRJzM= 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 Tue, Sep 16, 2025 at 01:12:52PM -0600, Jane Chu wrote: > commit 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared count") > introduced ->pt_share_count dedicated to hugetlb PMD share count tracking, > but omitted fixing copy_hugetlb_page_range(), leaving the function relying on > page_count() for tracking that no longer works. > > When lazy page table copy for hugetlb is disabled, that is, revert > commit bcd51a3c679d ("hugetlb: lazy page table copies in fork()") > fork()'ing with hugetlb PMD sharing quickly lockup - > > [ 239.446559] watchdog: BUG: soft lockup - CPU#75 stuck for 27s! > [ 239.446611] RIP: 0010:native_queued_spin_lock_slowpath+0x7e/0x2e0 > [ 239.446631] Call Trace: > [ 239.446633] > [ 239.446636] _raw_spin_lock+0x3f/0x60 > [ 239.446639] copy_hugetlb_page_range+0x258/0xb50 > [ 239.446645] copy_page_range+0x22b/0x2c0 > [ 239.446651] dup_mmap+0x3e2/0x770 > [ 239.446654] dup_mm.constprop.0+0x5e/0x230 > [ 239.446657] copy_process+0xd17/0x1760 > [ 239.446660] kernel_clone+0xc0/0x3e0 > [ 239.446661] __do_sys_clone+0x65/0xa0 > [ 239.446664] do_syscall_64+0x82/0x930 > [ 239.446668] ? count_memcg_events+0xd2/0x190 > [ 239.446671] ? syscall_trace_enter+0x14e/0x1f0 > [ 239.446676] ? syscall_exit_work+0x118/0x150 > [ 239.446677] ? arch_exit_to_user_mode_prepare.constprop.0+0x9/0xb0 > [ 239.446681] ? clear_bhb_loop+0x30/0x80 > [ 239.446684] ? clear_bhb_loop+0x30/0x80 > [ 239.446686] entry_SYSCALL_64_after_hwframe+0x76/0x7e > > There are two options to resolve the potential latent issue: > 1. warn against PMD sharing in copy_hugetlb_page_range(), > 2. fix it. > This patch opts for the second option. > While at it, simplify the comment, the details are not actually relevant > anymore. > > Fixes: 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared count") > Signed-off-by: Jane Chu > Reviewed-by: Harry Yoo Acked-by: Oscar Salvador Thanks -- Oscar Salvador SUSE Labs