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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pPlpL-001HwV-1L; Wed, 08 Feb 2023 14:53:39 +0000 From: "Matthew Wilcox (Oracle)" To: linux-xfs@vger.kernel.org, linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Cc: "Matthew Wilcox (Oracle)" Subject: [PATCH 3/3] mm: Hold the RCU read lock over calls to ->map_pages Date: Wed, 8 Feb 2023 14:53:35 +0000 Message-Id: <20230208145335.307287-4-willy@infradead.org> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20230208145335.307287-1-willy@infradead.org> References: <20230208145335.307287-1-willy@infradead.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 2DE6512001B X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: 7ukrmp1f8zwuxex398ydq4psxg5fdbi4 X-HE-Tag: 1675868030-504109 X-HE-Meta: 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 iF3Eltea Iau+CdNxbJveyz1RTMb20nTAioRou5q/OxB2QiMNNLVG2iS3YMOc4xCrlgID0tANLmf8mZ7piWQdOOTfPCX4eAOUvNS3CI5PG8wZD70SHp6tnWzAYtAgx3LMwdL2OOVYKC/BcRsAFeQ1z5O18JDangSk5eRlc0pFn5LbDKkY9Hh0GYkNfkZeCjgjG4h1z3F8Gek8mpAuqpfWBzY2X0tgJsXRVVEycO36sUmLbSbsHuK1Ca16jYMA3iUkP7w== 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: Prevent filesystems from doing things which sleep in their map_pages method. This is in preparation for a pagefault path protected only by RCU. Signed-off-by: Matthew Wilcox (Oracle) --- Documentation/filesystems/locking.rst | 4 ++-- mm/memory.c | 7 ++++++- 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index 922886fefb7f..8a80390446ba 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -645,7 +645,7 @@ ops mmap_lock PageLocked(page) open: yes close: yes fault: yes can return with page locked -map_pages: yes +map_pages: read page_mkwrite: yes can return with page locked pfn_mkwrite: yes access: yes @@ -661,7 +661,7 @@ locked. The VM will unlock the page. ->map_pages() is called when VM asks to map easy accessible pages. Filesystem should find and map pages associated with offsets from "start_pgoff" -till "end_pgoff". ->map_pages() is called with page table locked and must +till "end_pgoff". ->map_pages() is called with the RCU lock held and must not block. If it's not possible to reach a page without blocking, filesystem should skip it. Filesystem should use set_pte_range() to setup page table entry. Pointer to entry associated with the page is passed in diff --git a/mm/memory.c b/mm/memory.c index f1cf47b7e3bb..77577a1d09ac 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4442,6 +4442,7 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) unsigned long address = vmf->address, nr_pages, mask; pgoff_t start_pgoff = vmf->pgoff; pgoff_t end_pgoff; + vm_fault_t ret; int off; nr_pages = READ_ONCE(fault_around_bytes) >> PAGE_SHIFT; @@ -4467,7 +4468,11 @@ static vm_fault_t do_fault_around(struct vm_fault *vmf) return VM_FAULT_OOM; } - return vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); + rcu_read_lock(); + ret = vmf->vma->vm_ops->map_pages(vmf, start_pgoff, end_pgoff); + rcu_read_unlock(); + + return ret; } /* Return true if we should do read fault-around, false otherwise */ -- 2.35.1