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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 C69E8C43381 for ; Tue, 19 Mar 2019 10:40:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7F3FA2085A for ; Tue, 19 Mar 2019 10:40:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726717AbfCSKkT (ORCPT ); Tue, 19 Mar 2019 06:40:19 -0400 Received: from relmlor1.renesas.com ([210.160.252.171]:19865 "EHLO relmlie5.idc.renesas.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726661AbfCSKkT (ORCPT ); Tue, 19 Mar 2019 06:40:19 -0400 X-IronPort-AV: E=Sophos;i="5.58,497,1544454000"; d="scan'208";a="10783717" Received: from unknown (HELO relmlir5.idc.renesas.com) ([10.200.68.151]) by relmlie5.idc.renesas.com with ESMTP; 19 Mar 2019 19:40:16 +0900 Received: from localhost.localdomain (unknown [10.166.252.89]) by relmlir5.idc.renesas.com (Postfix) with ESMTP id 55ABF4020DB2; Tue, 19 Mar 2019 19:40:16 +0900 (JST) From: Yoshihiro Shimoda To: thierry.reding@gmail.com Cc: linux-pwm@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Phong Hoang , Yoshihiro Shimoda Subject: [PATCH v3] pwm: Fix deadlock warning when removing PWM device Date: Tue, 19 Mar 2019 19:40:08 +0900 Message-Id: <1552992008-20218-1-git-send-email-yoshihiro.shimoda.uh@renesas.com> X-Mailer: git-send-email 2.7.4 Sender: linux-renesas-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-renesas-soc@vger.kernel.org From: Phong Hoang This patch fixes deadlock warning if removing PWM device when CONFIG_PROVE_LOCKING is enabled. This issue can be reproceduced by the following steps on the R-Car H3 Salvator-X board if the backlight is disabled: # cd /sys/class/pwm/pwmchip0 # echo 0 > export # ls device export npwm power pwm0 subsystem uevent unexport # cd device/driver # ls bind e6e31000.pwm uevent unbind # echo e6e31000.pwm > unbind [ 87.659974] ====================================================== [ 87.666149] WARNING: possible circular locking dependency detected [ 87.672327] 5.0.0 #7 Not tainted [ 87.675549] ------------------------------------------------------ [ 87.681723] bash/2986 is trying to acquire lock: [ 87.686337] 000000005ea0e178 (kn->count#58){++++}, at: kernfs_remove_by_name_ns+0x50/0xa0 [ 87.694528] [ 87.694528] but task is already holding lock: [ 87.700353] 000000006313b17c (pwm_lock){+.+.}, at: pwmchip_remove+0x28/0x13c [ 87.707405] [ 87.707405] which lock already depends on the new lock. [ 87.707405] [ 87.715574] [ 87.715574] the existing dependency chain (in reverse order) is: [ 87.723048] [ 87.723048] -> #1 (pwm_lock){+.+.}: [ 87.728017] __mutex_lock+0x70/0x7e4 [ 87.732108] mutex_lock_nested+0x1c/0x24 [ 87.736547] pwm_request_from_chip.part.6+0x34/0x74 [ 87.741940] pwm_request_from_chip+0x20/0x40 [ 87.746725] export_store+0x6c/0x1f4 [ 87.750820] dev_attr_store+0x18/0x28 [ 87.754998] sysfs_kf_write+0x54/0x64 [ 87.759175] kernfs_fop_write+0xe4/0x1e8 [ 87.763615] __vfs_write+0x40/0x184 [ 87.767619] vfs_write+0xa8/0x19c [ 87.771448] ksys_write+0x58/0xbc [ 87.775278] __arm64_sys_write+0x18/0x20 [ 87.779721] el0_svc_common+0xd0/0x124 [ 87.783986] el0_svc_compat_handler+0x1c/0x24 [ 87.788858] el0_svc_compat+0x8/0x18 [ 87.792947] [ 87.792947] -> #0 (kn->count#58){++++}: [ 87.798260] lock_acquire+0xc4/0x22c [ 87.802353] __kernfs_remove+0x258/0x2c4 [ 87.806790] kernfs_remove_by_name_ns+0x50/0xa0 [ 87.811836] remove_files.isra.1+0x38/0x78 [ 87.816447] sysfs_remove_group+0x48/0x98 [ 87.820971] sysfs_remove_groups+0x34/0x4c [ 87.825583] device_remove_attrs+0x6c/0x7c [ 87.830197] device_del+0x11c/0x33c [ 87.834201] device_unregister+0x14/0x2c [ 87.838638] pwmchip_sysfs_unexport+0x40/0x4c [ 87.843509] pwmchip_remove+0xf4/0x13c [ 87.847773] rcar_pwm_remove+0x28/0x34 [ 87.852039] platform_drv_remove+0x24/0x64 [ 87.856651] device_release_driver_internal+0x18c/0x21c [ 87.862391] device_release_driver+0x14/0x1c [ 87.867175] unbind_store+0xe0/0x124 [ 87.871265] drv_attr_store+0x20/0x30 [ 87.875442] sysfs_kf_write+0x54/0x64 [ 87.879618] kernfs_fop_write+0xe4/0x1e8 [ 87.884055] __vfs_write+0x40/0x184 [ 87.888057] vfs_write+0xa8/0x19c [ 87.891887] ksys_write+0x58/0xbc [ 87.895716] __arm64_sys_write+0x18/0x20 [ 87.900154] el0_svc_common+0xd0/0x124 [ 87.904417] el0_svc_compat_handler+0x1c/0x24 [ 87.909289] el0_svc_compat+0x8/0x18 [ 87.913378] [ 87.913378] other info that might help us debug this: [ 87.913378] [ 87.921374] Possible unsafe locking scenario: [ 87.921374] [ 87.927286] CPU0 CPU1 [ 87.931808] ---- ---- [ 87.936331] lock(pwm_lock); [ 87.939293] lock(kn->count#58); [ 87.945120] lock(pwm_lock); [ 87.950599] lock(kn->count#58); [ 87.953908] [ 87.953908] *** DEADLOCK *** [ 87.953908] [ 87.959821] 4 locks held by bash/2986: [ 87.963563] #0: 00000000ace7bc30 (sb_writers#6){.+.+}, at: vfs_write+0x188/0x19c [ 87.971044] #1: 00000000287991b2 (&of->mutex){+.+.}, at: kernfs_fop_write+0xb4/0x1e8 [ 87.978872] #2: 00000000f739d016 (&dev->mutex){....}, at: device_release_driver_internal+0x40/0x21c [ 87.988001] #3: 000000006313b17c (pwm_lock){+.+.}, at: pwmchip_remove+0x28/0x13c [ 87.995481] [ 87.995481] stack backtrace: [ 87.999836] CPU: 0 PID: 2986 Comm: bash Not tainted 5.0.0 #7 [ 88.005489] Hardware name: Renesas Salvator-X board based on r8a7795 ES1.x (DT) [ 88.012791] Call trace: [ 88.015235] dump_backtrace+0x0/0x190 [ 88.018891] show_stack+0x14/0x1c [ 88.022204] dump_stack+0xb0/0xec [ 88.025514] print_circular_bug.isra.32+0x1d0/0x2e0 [ 88.030385] __lock_acquire+0x1318/0x1864 [ 88.034388] lock_acquire+0xc4/0x22c [ 88.037958] __kernfs_remove+0x258/0x2c4 [ 88.041874] kernfs_remove_by_name_ns+0x50/0xa0 [ 88.046398] remove_files.isra.1+0x38/0x78 [ 88.050487] sysfs_remove_group+0x48/0x98 [ 88.054490] sysfs_remove_groups+0x34/0x4c [ 88.058580] device_remove_attrs+0x6c/0x7c [ 88.062671] device_del+0x11c/0x33c [ 88.066154] device_unregister+0x14/0x2c [ 88.070070] pwmchip_sysfs_unexport+0x40/0x4c [ 88.074421] pwmchip_remove+0xf4/0x13c [ 88.078163] rcar_pwm_remove+0x28/0x34 [ 88.081906] platform_drv_remove+0x24/0x64 [ 88.085996] device_release_driver_internal+0x18c/0x21c [ 88.091215] device_release_driver+0x14/0x1c [ 88.095478] unbind_store+0xe0/0x124 [ 88.099048] drv_attr_store+0x20/0x30 [ 88.102704] sysfs_kf_write+0x54/0x64 [ 88.106359] kernfs_fop_write+0xe4/0x1e8 [ 88.110275] __vfs_write+0x40/0x184 [ 88.113757] vfs_write+0xa8/0x19c [ 88.117065] ksys_write+0x58/0xbc [ 88.120374] __arm64_sys_write+0x18/0x20 [ 88.124291] el0_svc_common+0xd0/0x124 [ 88.128034] el0_svc_compat_handler+0x1c/0x24 [ 88.132384] el0_svc_compat+0x8/0x18 The sysfs unexport in pwmchip_remove() is completely asymmetric to what we do in pwmchip_add_with_polarity() and commit 0733424c9ba9 ("pwm: Unexport children before chip removal") is a strong indication that this was wrong to begin with. We should just move pwmchip_sysfs_unexport() where it belongs, which is right after pwmchip_sysfs_unexport_children(). In that case, we do not need separate functions anymore either. We also really want to remove sysfs irrespective of whether or not the chip will be removed as a result of pwmchip_remove(). We can only assume that the driver will be gone after that, so we shouldn't leave any dangling sysfs files around. This warning disappears if we move pwmchip_sysfs_unexport() to the top of pwmchip_remove(), pwmchip_sysfs_unexport_children(). That way it is also outside of the pwm_lock section, which indeed doesn't seem to be needed. Moving the pwmchip_sysfs_export() call outside of that section also seems fine and it'd be perfectly symmetric with pwmchip_remove() again. So, this patch fixes them. Signed-off-by: Phong Hoang [shimoda: revise the commit log and code] Fixes: 76abbdde2d95 ("pwm: Add sysfs interface") Fixes: 0733424c9ba9 ("pwm: Unexport children before chip removal") Signed-off-by: Yoshihiro Shimoda Tested-by: Hoan Nguyen An Reviewed-by: Geert Uytterhoeven --- Changes from v2 (https://patchwork.kernel.org/patch/10850711/) - Revise the commit log. - Reduce code diff lines by using if (!parent) condition. - Add Reviewed-by Geert's tag. Changes from v1 (https://patchwork.kernel.org/patch/10848567/): - Change the subject from "Avoid" to "Fix". - Merge pwmchip_sysfs_unexport_children()'s code into pwmchip_sysfs_unexport() and move pwmchip_sysfs_unexport() to the top of pwmchip_remove(). - Revise the commit log that is reffered from Therry's comments [1] because it seems very clear to me. - Add Fixes tag about the commit 0733424c9ba9. - I got Geert's Reviewed-by on v1 patch, but I'm not sure I can add the Reviewed-by because v2 patch changes a bit. So, I didn't add the Reviewed-by tag. [1] https://www.mail-archive.com/linux-renesas-soc@vger.kernel.org/msg39167.html drivers/pwm/core.c | 10 +++++----- drivers/pwm/sysfs.c | 14 +------------- include/linux/pwm.h | 5 ----- 3 files changed, 6 insertions(+), 23 deletions(-) diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c index 1581f6a..c45e571 100644 --- a/drivers/pwm/core.c +++ b/drivers/pwm/core.c @@ -311,10 +311,12 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip, if (IS_ENABLED(CONFIG_OF)) of_pwmchip_add(chip); - pwmchip_sysfs_export(chip); - out: mutex_unlock(&pwm_lock); + + if (!ret) + pwmchip_sysfs_export(chip); + return ret; } EXPORT_SYMBOL_GPL(pwmchip_add_with_polarity); @@ -348,7 +350,7 @@ int pwmchip_remove(struct pwm_chip *chip) unsigned int i; int ret = 0; - pwmchip_sysfs_unexport_children(chip); + pwmchip_sysfs_unexport(chip); mutex_lock(&pwm_lock); @@ -368,8 +370,6 @@ int pwmchip_remove(struct pwm_chip *chip) free_pwms(chip); - pwmchip_sysfs_unexport(chip); - out: mutex_unlock(&pwm_lock); return ret; diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c index ceb233d..13d9bd5 100644 --- a/drivers/pwm/sysfs.c +++ b/drivers/pwm/sysfs.c @@ -411,19 +411,6 @@ void pwmchip_sysfs_export(struct pwm_chip *chip) void pwmchip_sysfs_unexport(struct pwm_chip *chip) { struct device *parent; - - parent = class_find_device(&pwm_class, NULL, chip, - pwmchip_sysfs_match); - if (parent) { - /* for class_find_device() */ - put_device(parent); - device_unregister(parent); - } -} - -void pwmchip_sysfs_unexport_children(struct pwm_chip *chip) -{ - struct device *parent; unsigned int i; parent = class_find_device(&pwm_class, NULL, chip, @@ -439,6 +426,7 @@ void pwmchip_sysfs_unexport_children(struct pwm_chip *chip) } put_device(parent); + device_unregister(parent); } static int __init pwm_sysfs_init(void) diff --git a/include/linux/pwm.h b/include/linux/pwm.h index d5199b5..ea3939f 100644 --- a/include/linux/pwm.h +++ b/include/linux/pwm.h @@ -597,7 +597,6 @@ static inline void pwm_remove_table(struct pwm_lookup *table, size_t num) #ifdef CONFIG_PWM_SYSFS void pwmchip_sysfs_export(struct pwm_chip *chip); void pwmchip_sysfs_unexport(struct pwm_chip *chip); -void pwmchip_sysfs_unexport_children(struct pwm_chip *chip); #else static inline void pwmchip_sysfs_export(struct pwm_chip *chip) { @@ -606,10 +605,6 @@ static inline void pwmchip_sysfs_export(struct pwm_chip *chip) static inline void pwmchip_sysfs_unexport(struct pwm_chip *chip) { } - -static inline void pwmchip_sysfs_unexport_children(struct pwm_chip *chip) -{ -} #endif /* CONFIG_PWM_SYSFS */ #endif /* __LINUX_PWM_H */ -- 2.7.4