From patchwork Wed Jun 3 14:49:44 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Ahmed S. Darwish" X-Patchwork-Id: 1303028 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linutronix.de Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 49cX0g3pYrz9sRR for ; Thu, 4 Jun 2020 00:51:15 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726106AbgFCOuK (ORCPT ); Wed, 3 Jun 2020 10:50:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59662 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726294AbgFCOuG (ORCPT ); Wed, 3 Jun 2020 10:50:06 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6FAA2C08C5C2; Wed, 3 Jun 2020 07:50:06 -0700 (PDT) Received: from [5.158.153.53] (helo=debian-buster-darwi.lab.linutronix.de.) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1jgUiJ-0001vC-NA; Wed, 03 Jun 2020 16:49:55 +0200 From: "Ahmed S. Darwish" To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Thomas Gleixner , "Paul E. McKenney" , "Sebastian A. Siewior" , Steven Rostedt , LKML , "Ahmed S. Darwish" , "David S. Miller" , Jakub Kicinski , Eric Dumazet , Stephen Hemminger , netdev@vger.kernel.org Subject: [PATCH v2 1/6] net: core: device_rename: Use rwsem instead of a seqcount Date: Wed, 3 Jun 2020 16:49:44 +0200 Message-Id: <20200603144949.1122421-2-a.darwish@linutronix.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200603144949.1122421-1-a.darwish@linutronix.de> References: <20200603144949.1122421-1-a.darwish@linutronix.de> MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Sequence counters write paths are critical sections that must never be preempted, and blocking, even for CONFIG_PREEMPTION=n, is not allowed. Commit 5dbe7c178d3f ("net: fix kernel deadlock with interface rename and netdev name retrieval.") handled a deadlock, observed with CONFIG_PREEMPTION=n, where the devnet_rename seqcount read side was infinitely spinning: it got scheduled after the seqcount write side blocked inside its own critical section. To fix that deadlock, among other issues, the commit added a cond_resched() inside the read side section. While this will get the non-preemptible kernel eventually unstuck, the seqcount reader is fully exhausting its slice just spinning -- until TIF_NEED_RESCHED is set. The fix is also still broken: if the seqcount reader belongs to a real-time scheduling policy, it can spin forever and the kernel will livelock. Disabling preemption over the seqcount write side critical section will not work: inside it are a number of GFP_KERNEL allocations and mutex locking through the drivers/base/ :: device_rename() call chain. From all the above, replace the seqcount with a rwsem. Fixes: 5dbe7c178d3f (net: fix kernel deadlock with interface rename and netdev name retrieval.) Fixes: 30e6c9fa93cf (net: devnet_rename_seq should be a seqcount) Fixes: c91f6df2db49 (sockopt: Change getsockopt() of SO_BINDTODEVICE to return an interface name) Cc: Reported-by: kbuild test robot [ v1 missing up_read() on error exit ] Reported-by: Dan Carpenter [ v1 missing up_read() on error exit ] Signed-off-by: Ahmed S. Darwish Reviewed-by: Sebastian Andrzej Siewior --- net/core/dev.c | 40 ++++++++++++++++++---------------------- 1 file changed, 18 insertions(+), 22 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index 2d8aceee4284..93a279ab4e97 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -79,6 +79,7 @@ #include #include #include +#include #include #include #include @@ -194,7 +195,7 @@ static DEFINE_SPINLOCK(napi_hash_lock); static unsigned int napi_gen_id = NR_CPUS; static DEFINE_READ_MOSTLY_HASHTABLE(napi_hash, 8); -static seqcount_t devnet_rename_seq; +static DECLARE_RWSEM(devnet_rename_sem); static inline void dev_base_seq_inc(struct net *net) { @@ -930,33 +931,28 @@ EXPORT_SYMBOL(dev_get_by_napi_id); * @net: network namespace * @name: a pointer to the buffer where the name will be stored. * @ifindex: the ifindex of the interface to get the name from. - * - * The use of raw_seqcount_begin() and cond_resched() before - * retrying is required as we want to give the writers a chance - * to complete when CONFIG_PREEMPTION is not set. */ int netdev_get_name(struct net *net, char *name, int ifindex) { struct net_device *dev; - unsigned int seq; + int ret; -retry: - seq = raw_seqcount_begin(&devnet_rename_seq); + down_read(&devnet_rename_sem); rcu_read_lock(); + dev = dev_get_by_index_rcu(net, ifindex); if (!dev) { - rcu_read_unlock(); - return -ENODEV; + ret = -ENODEV; + goto out; } strcpy(name, dev->name); - rcu_read_unlock(); - if (read_seqcount_retry(&devnet_rename_seq, seq)) { - cond_resched(); - goto retry; - } - return 0; + ret = 0; +out: + rcu_read_unlock(); + up_read(&devnet_rename_sem); + return ret; } /** @@ -1228,10 +1224,10 @@ int dev_change_name(struct net_device *dev, const char *newname) likely(!(dev->priv_flags & IFF_LIVE_RENAME_OK))) return -EBUSY; - write_seqcount_begin(&devnet_rename_seq); + down_write(&devnet_rename_sem); if (strncmp(newname, dev->name, IFNAMSIZ) == 0) { - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); return 0; } @@ -1239,7 +1235,7 @@ int dev_change_name(struct net_device *dev, const char *newname) err = dev_get_valid_name(net, dev, newname); if (err < 0) { - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); return err; } @@ -1254,11 +1250,11 @@ int dev_change_name(struct net_device *dev, const char *newname) if (ret) { memcpy(dev->name, oldname, IFNAMSIZ); dev->name_assign_type = old_assign_type; - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); return ret; } - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); netdev_adjacent_rename_links(dev, oldname); @@ -1279,7 +1275,7 @@ int dev_change_name(struct net_device *dev, const char *newname) /* err >= 0 after dev_alloc_name() or stores the first errno */ if (err >= 0) { err = ret; - write_seqcount_begin(&devnet_rename_seq); + down_write(&devnet_rename_sem); memcpy(dev->name, oldname, IFNAMSIZ); memcpy(oldname, newname, IFNAMSIZ); dev->name_assign_type = old_assign_type; From patchwork Wed Jun 3 14:49:45 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Ahmed S. Darwish" X-Patchwork-Id: 1303024 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linutronix.de Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 49cWzl3cFmz9sRW for ; Thu, 4 Jun 2020 00:50:27 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726050AbgFCOuZ (ORCPT ); Wed, 3 Jun 2020 10:50:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59708 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726414AbgFCOuT (ORCPT ); Wed, 3 Jun 2020 10:50:19 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 82937C08C5C0; Wed, 3 Jun 2020 07:50:19 -0700 (PDT) Received: from [5.158.153.53] (helo=debian-buster-darwi.lab.linutronix.de.) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1jgUiP-0001w5-0A; Wed, 03 Jun 2020 16:50:01 +0200 From: "Ahmed S. Darwish" To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Thomas Gleixner , "Paul E. McKenney" , "Sebastian A. Siewior" , Steven Rostedt , LKML , "Ahmed S. Darwish" , Andrew Lunn , Florian Fainelli , Heiner Kallweit , Russell King , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org Subject: [PATCH v2 2/6] net: phy: fixed_phy: Remove unused seqcount Date: Wed, 3 Jun 2020 16:49:45 +0200 Message-Id: <20200603144949.1122421-3-a.darwish@linutronix.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200603144949.1122421-1-a.darwish@linutronix.de> References: <20200603144949.1122421-1-a.darwish@linutronix.de> MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Commit bf7afb29d545 ("phy: improve safety of fixed-phy MII register reading") protected the fixed PHY status with a sequence counter. Two years later, commit d2b977939b18 ("net: phy: fixed-phy: remove fixed_phy_update_state()") removed the sequence counter's write side critical section -- neutralizing its read side retry loop. Remove the unused seqcount. Signed-off-by: Ahmed S. Darwish Reviewed-by: Sebastian Andrzej Siewior Reviewed-by: Andrew Lunn --- drivers/net/phy/fixed_phy.c | 26 ++++++++++---------------- 1 file changed, 10 insertions(+), 16 deletions(-) diff --git a/drivers/net/phy/fixed_phy.c b/drivers/net/phy/fixed_phy.c index 4a3d34f40cb9..c4641b1704d6 100644 --- a/drivers/net/phy/fixed_phy.c +++ b/drivers/net/phy/fixed_phy.c @@ -19,7 +19,6 @@ #include #include #include -#include #include #include #include @@ -34,7 +33,6 @@ struct fixed_mdio_bus { struct fixed_phy { int addr; struct phy_device *phydev; - seqcount_t seqcount; struct fixed_phy_status status; bool no_carrier; int (*link_update)(struct net_device *, struct fixed_phy_status *); @@ -80,19 +78,17 @@ static int fixed_mdio_read(struct mii_bus *bus, int phy_addr, int reg_num) list_for_each_entry(fp, &fmb->phys, node) { if (fp->addr == phy_addr) { struct fixed_phy_status state; - int s; - do { - s = read_seqcount_begin(&fp->seqcount); - fp->status.link = !fp->no_carrier; - /* Issue callback if user registered it. */ - if (fp->link_update) - fp->link_update(fp->phydev->attached_dev, - &fp->status); - /* Check the GPIO for change in status */ - fixed_phy_update(fp); - state = fp->status; - } while (read_seqcount_retry(&fp->seqcount, s)); + fp->status.link = !fp->no_carrier; + + /* Issue callback if user registered it. */ + if (fp->link_update) + fp->link_update(fp->phydev->attached_dev, + &fp->status); + + /* Check the GPIO for change in status */ + fixed_phy_update(fp); + state = fp->status; return swphy_read_reg(reg_num, &state); } @@ -150,8 +146,6 @@ static int fixed_phy_add_gpiod(unsigned int irq, int phy_addr, if (!fp) return -ENOMEM; - seqcount_init(&fp->seqcount); - if (irq != PHY_POLL) fmb->mii_bus->irq[phy_addr] = irq; From patchwork Wed Jun 3 14:49:46 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "Ahmed S. Darwish" X-Patchwork-Id: 1303023 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linutronix.de Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 49cWzh3k69z9sT5 for ; Thu, 4 Jun 2020 00:50:24 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726398AbgFCOuW (ORCPT ); Wed, 3 Jun 2020 10:50:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59702 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726397AbgFCOuT (ORCPT ); Wed, 3 Jun 2020 10:50:19 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2E962C08C5C2; Wed, 3 Jun 2020 07:50:17 -0700 (PDT) Received: from [5.158.153.53] (helo=debian-buster-darwi.lab.linutronix.de.) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1jgUiT-0001xi-Uy; Wed, 03 Jun 2020 16:50:06 +0200 From: "Ahmed S. Darwish" To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Thomas Gleixner , "Paul E. McKenney" , "Sebastian A. Siewior" , Steven Rostedt , LKML , "Ahmed S. Darwish" , Eric Dumazet , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org Subject: [PATCH v2 3/6] u64_stats: Document writer non-preemptibility requirement Date: Wed, 3 Jun 2020 16:49:46 +0200 Message-Id: <20200603144949.1122421-4-a.darwish@linutronix.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200603144949.1122421-1-a.darwish@linutronix.de> References: <20200603144949.1122421-1-a.darwish@linutronix.de> MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The u64_stats mechanism uses sequence counters to protect against 64-bit values tearing on 32-bit architectures. Updating such statistics is a sequence counter write side critical section. Preemption must be disabled before entering this seqcount write critical section. Failing to do so, the seqcount read side can preempt the write side section and spin for the entire scheduler tick. If that reader belongs to a real-time scheduling class, it can spin forever and the kernel will livelock. Document this statistics update side non-preemptibility requirement. Reword the introductory paragraph to highlight u64_stats raison d'être: 64-bit values tearing protection on 32-bit architectures. Divide documentation on a basis of internal design vs. usage constraints. Reword the u64_stats header file top comment to always mention "Reader" or "Writer" at the start of each bullet point, making it easier to follow which side each point is actually for. Clarify the statement "whole thing is a NOOP on 64bit arches or UP kernels". For 32-bit UP kernels, preemption is always disabled for the statistics read side section. Signed-off-by: Ahmed S. Darwish Reviewed-by: Sebastian Andrzej Siewior --- include/linux/u64_stats_sync.h | 43 ++++++++++++++++++---------------- 1 file changed, 23 insertions(+), 20 deletions(-) diff --git a/include/linux/u64_stats_sync.h b/include/linux/u64_stats_sync.h index 9de5c10293f5..c6abb79501b3 100644 --- a/include/linux/u64_stats_sync.h +++ b/include/linux/u64_stats_sync.h @@ -3,33 +3,36 @@ #define _LINUX_U64_STATS_SYNC_H /* - * To properly implement 64bits network statistics on 32bit and 64bit hosts, - * we provide a synchronization point, that is a noop on 64bit or UP kernels. + * Protect against 64-bit values tearing on 32-bit architectures. This is + * typically used for statistics read/update in different subsystems. * * Key points : - * 1) Use a seqcount on SMP 32bits, with low overhead. - * 2) Whole thing is a noop on 64bit arches or UP kernels. - * 3) Write side must ensure mutual exclusion or one seqcount update could + * + * - Use a seqcount on 32-bit SMP, only disable preemption for 32-bit UP. + * - The whole thing is a no-op on 64-bit architectures. + * + * Usage constraints: + * + * 1) Write side must ensure mutual exclusion, or one seqcount update could * be lost, thus blocking readers forever. - * If this synchronization point is not a mutex, but a spinlock or - * spinlock_bh() or disable_bh() : - * 3.1) Write side should not sleep. - * 3.2) Write side should not allow preemption. - * 3.3) If applicable, interrupts should be disabled. + * + * 2) Write side must disable preemption, or a seqcount reader can preempt the + * writer and also spin forever. + * + * 3) Write side must use the _irqsave() variant if other writers, or a reader, + * can be invoked from an IRQ context. * * 4) If reader fetches several counters, there is no guarantee the whole values - * are consistent (remember point 1) : this is a noop on 64bit arches anyway) + * are consistent w.r.t. each other (remember point #2: seqcounts are not + * used for 64bit architectures). * - * 5) readers are allowed to sleep or be preempted/interrupted : They perform - * pure reads. But if they have to fetch many values, it's better to not allow - * preemptions/interruptions to avoid many retries. + * 5) Readers are allowed to sleep or be preempted/interrupted: they perform + * pure reads. * - * 6) If counter might be written by an interrupt, readers should block interrupts. - * (On UP, there is no seqcount_t protection, a reader allowing interrupts could - * read partial values) - * - * 7) For irq and softirq uses, readers can use u64_stats_fetch_begin_irq() and - * u64_stats_fetch_retry_irq() helpers + * 6) Readers must use both u64_stats_fetch_{begin,retry}_irq() if the stats + * might be updated from a hardirq or softirq context (remember point #1: + * seqcounts are not used for UP kernels). 32-bit UP stat readers could read + * corrupted 64-bit values otherwise. * * Usage : * From patchwork Wed Jun 3 14:49:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Ahmed S. Darwish" X-Patchwork-Id: 1303026 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=linutronix.de Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 49cX091s2Fz9sTL for ; Thu, 4 Jun 2020 00:50:49 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726690AbgFCOur (ORCPT ); Wed, 3 Jun 2020 10:50:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726450AbgFCOuW (ORCPT ); Wed, 3 Jun 2020 10:50:22 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1FF3FC08C5C0; Wed, 3 Jun 2020 07:50:22 -0700 (PDT) Received: from [5.158.153.53] (helo=debian-buster-darwi.lab.linutronix.de.) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.80) (envelope-from ) id 1jgUiZ-0001yp-5A; Wed, 03 Jun 2020 16:50:11 +0200 From: "Ahmed S. Darwish" To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Thomas Gleixner , "Paul E. McKenney" , "Sebastian A. Siewior" , Steven Rostedt , LKML , "Ahmed S. Darwish" , Andrew Lunn , Florian Fainelli , Heiner Kallweit , Russell King , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org Subject: [PATCH v2 4/6] net: mdiobus: Disable preemption upon u64_stats update Date: Wed, 3 Jun 2020 16:49:47 +0200 Message-Id: <20200603144949.1122421-5-a.darwish@linutronix.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200603144949.1122421-1-a.darwish@linutronix.de> References: <20200603144949.1122421-1-a.darwish@linutronix.de> MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The u64_stats mechanism uses sequence counters to protect against 64-bit values tearing on 32-bit architectures. Updating u64_stats is thus a sequence counter write side critical section where preemption must be disabled. For mdiobus_stats_acct(), disable preemption upon the u64_stats update. It is called from process context through mdiobus_read() and mdiobus_write(). Reported-by: kernel test robot Signed-off-by: Ahmed S. Darwish Reviewed-by: Sebastian Andrzej Siewior --- drivers/net/phy/mdio_bus.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c index 7a4eb3f2cb74..a1a4dee2a033 100644 --- a/drivers/net/phy/mdio_bus.c +++ b/drivers/net/phy/mdio_bus.c @@ -757,6 +757,7 @@ EXPORT_SYMBOL(mdiobus_scan); static void mdiobus_stats_acct(struct mdio_bus_stats *stats, bool op, int ret) { + preempt_disable(); u64_stats_update_begin(&stats->syncp); u64_stats_inc(&stats->transfers); @@ -771,6 +772,7 @@ static void mdiobus_stats_acct(struct mdio_bus_stats *stats, bool op, int ret) u64_stats_inc(&stats->writes); out: u64_stats_update_end(&stats->syncp); + preempt_enable(); } /**