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Mon, 2 Nov 2026 14:59:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793631608; bh=DA4U0m1CHtqk19BjQpd8o6fqolui3N68b+LzMS0kHTM=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=kIejajPLDhBhNAF+5qAkd+IjamKUOnO1hhgOl6ob3NywfSYo1UCCZClj+UVXxg6hN 8GZuczs7QvhEz8GqB31Q0v4Sfe6zaLku1E8g4bV1Nm7S11GUdX9udG3+A+XpQmpG4w SKp3yZE5RKwGE6D9RxNOhr665KUXvrAf7U9EgM6t8GMzBMTN1Hyi8S9DzqCn2e/KFT qYkBu+IipshrjT/yGx4WL5OycQQAysKT17bx+VTU/wQ//N1IctW6952TFgl4pmjQUh Zgj0NC/jh4zpBceIV8H3jC5zH7xmHBcraK25zYbCARrQ8e4MvgCvvVFdA3MjVOm0bI x3pJnolxi8+9Q== From: Christian Brauner Date: Mon, 02 Nov 2026 15:48:54 +0100 Subject: [PATCH RFC 14/16] fs/proc/vmcore: let procfs copy out reads X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , Precedence: list X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261102-work-procfs-core-v1-14-75df35e4f8b8@kernel.org> References: <20261102-work-procfs-core-v1-0-75df35e4f8b8@kernel.org> In-Reply-To: <20261102-work-procfs-core-v1-0-75df35e4f8b8@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: Linus Torvalds , Jann Horn , Josef Bacik , Chris Mason , Jeff Layton , NeilBrown , Eric Dumazet , Thomas Gleixner , Al Viro , Jonathan Corbet , Christoph Hellwig , Greg Kroah-Hartman , Joel Granados , Kees Cook , Jan Kara , Jan Kara , linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-um@lists.infradead.org, linux-wireless@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, ntfs3@lists.linux.dev, platform-driver-x86@vger.kernel.org, coreteam@netfilter.org, kexec@lists.infradead.org, linux-pci@vger.kernel.org, linux-sound@vger.kernel.org, netfilter-devel@vger.kernel.org, dri-devel@lists.freedesktop.org, ibm-acpi-devel@lists.sourceforge.net, jfs-discussion@lists.sourceforge.net, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cifs@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-mm@kvack.org, linux-sh@vger.kernel.org, linux-usb@vger.kernel.org, samba-technical@lists.samba.org, sparclinux@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-doc@vger.kernel.org, linux-serial@vger.kernel.org, linux-atm-general@lists.sourceforge.net, Takashi Iwai , linux-input@vger.kernel.org, linux-raid@vger.kernel.org, linux-ext4@vger.kernel.org, linux-modules@vger.kernel.org, linux-debuggers@vger.kernel.org, "Christian Brauner (Amutable)" , Chuck Lever X-Mailer: b4 0.17-dev X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Implement ->proc_read_buf() so procfs copies what is read to userspace after it unpinned the entry. __read_vmcore() fills procfs' buffer through a kvec iov_iter. So a read goes through that buffer now instead of straight from the old memory into the reader's, which is what splice() did already. mmap() isn't affected. On ppc64 a machine check while reading the old memory used to be recovered through the exception table of copy_to_user(), by accident. copy_oldmem_page() copies with _copy_mc_to_iter() now, so a read through procfs' buffer recovers from it as well. The buffer is 128k, which keeps the entry pinned for one such piece at a time, and /proc/vmcore asks for PROC_ENTRY_FULL_READS so that a larger read is filled in pieces. kexec-tools treats a short read of it as fatal. A read that faults on its buffer in a later piece returns the pieces before it now instead of failing with -EFAULT. fadump removes /proc/vmcore when its memory is released and that no longer waits for a reader that faults on its buffer. Signed-off-by: Christian Brauner (Amutable) --- fs/proc/vmcore.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c index ccb795b85509..1c1e71231f4e 100644 --- a/fs/proc/vmcore.c +++ b/fs/proc/vmcore.c @@ -27,6 +27,7 @@ #include #include #include +#include #include #include #include @@ -427,9 +428,14 @@ static ssize_t __read_vmcore(struct iov_iter *iter, loff_t *fpos) return acc; } -static ssize_t read_vmcore(struct kiocb *iocb, struct iov_iter *iter) +static ssize_t read_vmcore(struct file *file, char *buf, size_t count, + loff_t *ppos) { - return __read_vmcore(iter, &iocb->ki_pos); + struct kvec kvec = { .iov_base = buf, .iov_len = count }; + struct iov_iter iter; + + iov_iter_kvec(&iter, ITER_DEST, &kvec, 1, count); + return __read_vmcore(&iter, ppos); } /** @@ -709,9 +715,11 @@ static int mmap_vmcore(struct file *file, struct vm_area_struct *vma) #endif static const struct proc_ops vmcore_proc_ops = { + .proc_flags = PROC_ENTRY_FULL_READS, .proc_open = open_vmcore, .proc_release = release_vmcore, - .proc_read_iter = read_vmcore, + .proc_read_buf = read_vmcore, + .proc_read_size = SZ_128K, .proc_lseek = default_llseek, .proc_mmap = mmap_vmcore, }; -- 2.53.0