From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C8FDC43381 for ; Wed, 3 Mar 2021 14:33:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3917264E87 for ; Wed, 3 Mar 2021 14:33:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1383346AbhCCObQ (ORCPT ); Wed, 3 Mar 2021 09:31:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37970 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1842973AbhCCKXN (ORCPT ); Wed, 3 Mar 2021 05:23:13 -0500 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D439EC08ED3D for ; Wed, 3 Mar 2021 02:15:33 -0800 (PST) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1614766530; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6gxU8470dDzAP7HfvUdBdyr9yxuJ8C0WR83TSoe4VBA=; b=wLaCikomf2P6Oxm8LIkmjrb2bU8FHRzOEM+Zn+K7vd9QyjJUARrXvuhMFL88IItMKCOsRn 2hDuK5Mnk3QdNZzEwWQmyf1eQYobSHwhTwd1p8dTI2391RtfI5hyCbkIPCZX7o4CBlC1Wv iHvrF0ClHe9/Rhh0/zWVMHgUf7+W2XRgG/P2DIoR9SQyDkKnMDVY6LcIbCcECFfvP8q5UV niyBrtP93QzOwVS8HadngtRCjvIq+dFJ2q96eSrl+m6K3z1O0e+Agurp7QAqz8CyL+D2De PAG5YaMcTmKJrQM5jUNXEMZlR04GTOga9sVvTV7Bhn34MAOmSaYLjzmWxF7FYQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1614766530; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6gxU8470dDzAP7HfvUdBdyr9yxuJ8C0WR83TSoe4VBA=; b=ZrmfNsNhxCMROF7acvjvPMYwc+pkJ+Mwz+JUMkCX84ooKIniSA/zPyo4modHCjo7nioLhF FROcGMLz0zwxUfDg== To: Petr Mladek Cc: Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , linux-mtd@lists.infradead.org Subject: [PATCH next v4 02/15] mtd: mtdoops: synchronize kmsg_dumper Date: Wed, 3 Mar 2021 11:15:15 +0100 Message-Id: <20210303101528.29901-3-john.ogness@linutronix.de> In-Reply-To: <20210303101528.29901-1-john.ogness@linutronix.de> References: <20210303101528.29901-1-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The kmsg_dumper can be called from any context and CPU, possibly from multiple CPUs simultaneously. Since the writing of the buffer can occur from a later scheduled work queue, the oops buffer must be protected against simultaneous dumping. Use an atomic bit to mark when the buffer is protected. Release the protection in between setting the buffer and the actual writing in order for a possible panic (immediate write) to be written during the scheduling of a previous oops (delayed write). An atomic bit (rather than a spinlock) was chosen so that no scheduling or preemption side-effects would be introduced. The MTD kmsg_dumper may dump directly or it may be delayed (via scheduled work). Depending on the context, different MTD callbacks are used. For example, mtd_write() expects to be called in a non-atomic context and may take a mutex. Signed-off-by: John Ogness Reviewed-by: Petr Mladek --- drivers/mtd/mtdoops.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c index 774970bfcf85..8bbfba40a554 100644 --- a/drivers/mtd/mtdoops.c +++ b/drivers/mtd/mtdoops.c @@ -52,6 +52,7 @@ static struct mtdoops_context { int nextcount; unsigned long *oops_page_used; + unsigned long oops_buf_busy; void *oops_buf; } oops_cxt; @@ -180,6 +181,9 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) u32 *hdr; int ret; + if (test_and_set_bit(0, &cxt->oops_buf_busy)) + return; + /* Add mtdoops header to the buffer */ hdr = cxt->oops_buf; hdr[0] = cxt->nextcount; @@ -190,7 +194,7 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) record_size, &retlen, cxt->oops_buf); if (ret == -EOPNOTSUPP) { printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n"); - return; + goto out; } } else ret = mtd_write(mtd, cxt->nextpage * record_size, @@ -203,6 +207,8 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic) memset(cxt->oops_buf, 0xff, record_size); mtdoops_inc_counter(cxt); +out: + clear_bit(0, &cxt->oops_buf_busy); } static void mtdoops_workfunc_write(struct work_struct *work) @@ -276,8 +282,11 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper, if (reason == KMSG_DUMP_OOPS && !dump_oops) return; + if (test_and_set_bit(0, &cxt->oops_buf_busy)) + return; kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE, record_size - MTDOOPS_HEADER_SIZE, NULL); + clear_bit(0, &cxt->oops_buf_busy); if (reason != KMSG_DUMP_OOPS) { /* Panics must be written immediately */ @@ -394,6 +403,7 @@ static int __init mtdoops_init(void) return -ENOMEM; } memset(cxt->oops_buf, 0xff, record_size); + cxt->oops_buf_busy = 0; INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase); INIT_WORK(&cxt->work_write, mtdoops_workfunc_write); -- 2.20.1