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Tue, 20 Aug 2024 00:08:36 +0800 From: zhangchun To: CC: , , , , , , Subject: [PATCH v3] =?UTF-8?q?mm:=20Give=20kmap=5Flock=20before=20call=20flus?= =?UTF-8?q?h=5Ftlb=5Fkernel=5Frang=EF=BC=8Cavoid=20kmap=5Fhigh=20deadlock.?= Date: Tue, 20 Aug 2024 00:10:06 +0800 Message-ID: <1724083806-21956-1-git-send-email-zhang.chuna@h3c.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <20240723172609.7694b76e90bb18a0fd360ede@linux-foundation.org> References: <20240723172609.7694b76e90bb18a0fd360ede@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.99.206.13] X-ClientProxiedBy: BJSMTP01-EX.srv.huawei-3com.com (10.63.20.132) To DAG6EX09-BJD.srv.huawei-3com.com (10.153.34.11) X-DNSRBL: X-MAIL:h3cspam02-ex.h3c.com 47JG8lvc011045 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: CB5AB16003D X-Stat-Signature: ttnrnac3ic6hx9wa9px1in9u7nay851d X-Rspam-User: X-HE-Tag: 1724088036-60284 X-HE-Meta: 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 zPH8Kfak cKZvgfMwZbNFS7sfofVLqbaDBfVUlYjsKM12N5QvSu1jXgXEiXIKChaYvN4japwnFUp5hsM3pZzIZ7hzYmIWhc+YWUuXzJNqG/XgVddKUG1abBOyKuMRYQvvVOfGxNqQvIHzJ2ZAuZMRGRaa2VjgdjICn1GOtnvUOGmwRp8etSQeQarunusXtp/TF7bANgWbDkKNh8iR4Alb5aXK9NJPUi5d4FAKvPzkGSS2k9CI4MdSs9sMv6tuOvMN1I9EYSOJZHmoVaWoO+wLKfc4YAsmOCflyibJfLR+ljol7Eypze4q1IZYwpgVpptgVQEAyfWZAt/cHu4WW8IxYGxfuc38dpUmWsUlBseqYOjIl X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: CPU 0: CPU 1: kmap_high(){ kmap_xxx() { ... irq_disable(); spin_lock(&kmap_lock) ... map_new_virtual ... flush_all_zero_pkmaps flush_tlb_kernel_range /* CPU0 holds the kmap_lock */ smp_call_function_many spin_lock(&kmap_lock) ... .... spin_unlock(&kmap_lock) ... CPU 0 holds the kmap_lock, waiting for CPU 1 respond to IPI. But CPU 1 has disabled irqs, waiting for kmap_lock, cannot answer the IPI. Fix this by releasing kmap_lock before call flush_tlb_kernel_range, avoid kmap_lock deadlock. Like this: if (need_flush) { unlock_kmap(); flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP)); lock_kmap(); } Dropping the lock is safe. kmap_lock is used to protect pkmap_count, pkmap_page_table and last_pkmap_nr(static variable). When call flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP)), flush_tlb_kernel_range will neither modify nor read these variables. Leave that data unprotected here is safe. map_new_virtual aims to find an usable entry pkmap_count[last_pkmap_nr]. When read and modify the pkmap_count[last_pkmap_nr], the kmap_lock is not dropped. "if (!pkmap_count[last_pkmap_nr])" determine pkmap_count[last_pkmap_nr] is usable or not. If unusable, try agin. Furthermore, the value of static variable last_pkmap_nr is stored in a local variable last_pkmap_nr, when kmap_lock is acquired, this is thread-safe. In an extreme case, if Thread A and Thread B access the same last_pkmap_nr, Thread A calls function flush_tlb_kernel_range and release the kmap_lock, and Thread B then acquires the kmap_lock and modifies the variable pkmap_count[last_pkmap_nr]. After Thread A completes the execution of function flush_tlb_kernel_range, it will check the variable pkmap_count[last_pkmap_nr]. static inline unsigned long map_new_virtual(struct page *page) { unsigned long vaddr; int count; unsigned int last_pkmap_nr; // local variable to store static variable last_pkmap_nr unsigned int color = get_pkmap_color(page); start: ... flush_all_zero_pkmaps();// release kmap_lock, then acquire it count = get_pkmap_entries_count(color); } ... if (!pkmap_count[last_pkmap_nr]) // pkmap_count[last_pkmap_nr] is used or not break; /* Found a usable entry */ if (--count) continue; ... vaddr = PKMAP_ADDR(last_pkmap_nr); set_pte_at(&init_mm, vaddr, &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot)); pkmap_count[last_pkmap_nr] = 1; ... return vaddr; } Fixes: 3297e760776a ("highmem: atomic highmem kmap page pinning") Signed-off-by: zhangchun Co-developed-by: zhangzhansheng Signed-off-by: zhangzhansheng Suggested-by: Matthew Wilcox Reviewed-by: zhangzhengming --- mm/highmem.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/highmem.c b/mm/highmem.c index ef3189b..07f2c67 100644 --- a/mm/highmem.c +++ b/mm/highmem.c @@ -231,8 +231,18 @@ static void flush_all_zero_pkmaps(void) set_page_address(page, NULL); need_flush = 1; } - if (need_flush) + if (need_flush) { + /* + * In multi-core system one CPU holds the kmap_lock, waiting + * for other CPUs respond to IPI. But other CPUS has disabled + * irqs, waiting for kmap_lock, cannot answer the IPI. Release + * kmap_lock before call flush_tlb_kernel_range, avoid kmap_lock + * deadlock. + */ + unlock_kmap(); flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP)); + lock_kmap(); + } } void __kmap_flush_unused(void) -- 1.8.3.1