releases/4.19.51/pwm-fix-deadlock-warning-when-removing-pwm-device.patch

   1 From 692b6ebfa014c12f2778326d3613a70f388b9bf6 Mon Sep 17 00:00:00 2001
   2 From: Phong Hoang <phong.hoang.wz@renesas.com>
   3 Date: Tue, 19 Mar 2019 19:40:08 +0900
   4 Subject: pwm: Fix deadlock warning when removing PWM device
   5 MIME-Version: 1.0
   6 Content-Type: text/plain; charset=UTF-8
   7 Content-Transfer-Encoding: 8bit
   8
   9 [ Upstream commit 347ab9480313737c0f1aaa08e8f2e1a791235535 ]
  10
  11 This patch fixes deadlock warning if removing PWM device
  12 when CONFIG_PROVE_LOCKING is enabled.
  13
  14 This issue can be reproceduced by the following steps on
  15 the R-Car H3 Salvator-X board if the backlight is disabled:
  16
  17  # cd /sys/class/pwm/pwmchip0
  18  # echo 0 > export
  19  # ls
  20  device  export  npwm  power  pwm0  subsystem  uevent  unexport
  21  # cd device/driver
  22  # ls
  23  bind  e6e31000.pwm  uevent  unbind
  24  # echo e6e31000.pwm > unbind
  25
  26 [   87.659974] ======================================================
  27 [   87.666149] WARNING: possible circular locking dependency detected
  28 [   87.672327] 5.0.0 #7 Not tainted
  29 [   87.675549] ------------------------------------------------------
  30 [   87.681723] bash/2986 is trying to acquire lock:
  31 [   87.686337] 000000005ea0e178 (kn->count#58){++++}, at: kernfs_remove_by_name_ns+0x50/0xa0
  32 [   87.694528]
  33 [   87.694528] but task is already holding lock:
  34 [   87.700353] 000000006313b17c (pwm_lock){+.+.}, at: pwmchip_remove+0x28/0x13c
  35 [   87.707405]
  36 [   87.707405] which lock already depends on the new lock.
  37 [   87.707405]
  38 [   87.715574]
  39 [   87.715574] the existing dependency chain (in reverse order) is:
  40 [   87.723048]
  41 [   87.723048] -> #1 (pwm_lock){+.+.}:
  42 [   87.728017]        __mutex_lock+0x70/0x7e4
  43 [   87.732108]        mutex_lock_nested+0x1c/0x24
  44 [   87.736547]        pwm_request_from_chip.part.6+0x34/0x74
  45 [   87.741940]        pwm_request_from_chip+0x20/0x40
  46 [   87.746725]        export_store+0x6c/0x1f4
  47 [   87.750820]        dev_attr_store+0x18/0x28
  48 [   87.754998]        sysfs_kf_write+0x54/0x64
  49 [   87.759175]        kernfs_fop_write+0xe4/0x1e8
  50 [   87.763615]        __vfs_write+0x40/0x184
  51 [   87.767619]        vfs_write+0xa8/0x19c
  52 [   87.771448]        ksys_write+0x58/0xbc
  53 [   87.775278]        __arm64_sys_write+0x18/0x20
  54 [   87.779721]        el0_svc_common+0xd0/0x124
  55 [   87.783986]        el0_svc_compat_handler+0x1c/0x24
  56 [   87.788858]        el0_svc_compat+0x8/0x18
  57 [   87.792947]
  58 [   87.792947] -> #0 (kn->count#58){++++}:
  59 [   87.798260]        lock_acquire+0xc4/0x22c
  60 [   87.802353]        __kernfs_remove+0x258/0x2c4
  61 [   87.806790]        kernfs_remove_by_name_ns+0x50/0xa0
  62 [   87.811836]        remove_files.isra.1+0x38/0x78
  63 [   87.816447]        sysfs_remove_group+0x48/0x98
  64 [   87.820971]        sysfs_remove_groups+0x34/0x4c
  65 [   87.825583]        device_remove_attrs+0x6c/0x7c
  66 [   87.830197]        device_del+0x11c/0x33c
  67 [   87.834201]        device_unregister+0x14/0x2c
  68 [   87.838638]        pwmchip_sysfs_unexport+0x40/0x4c
  69 [   87.843509]        pwmchip_remove+0xf4/0x13c
  70 [   87.847773]        rcar_pwm_remove+0x28/0x34
  71 [   87.852039]        platform_drv_remove+0x24/0x64
  72 [   87.856651]        device_release_driver_internal+0x18c/0x21c
  73 [   87.862391]        device_release_driver+0x14/0x1c
  74 [   87.867175]        unbind_store+0xe0/0x124
  75 [   87.871265]        drv_attr_store+0x20/0x30
  76 [   87.875442]        sysfs_kf_write+0x54/0x64
  77 [   87.879618]        kernfs_fop_write+0xe4/0x1e8
  78 [   87.884055]        __vfs_write+0x40/0x184
  79 [   87.888057]        vfs_write+0xa8/0x19c
  80 [   87.891887]        ksys_write+0x58/0xbc
  81 [   87.895716]        __arm64_sys_write+0x18/0x20
  82 [   87.900154]        el0_svc_common+0xd0/0x124
  83 [   87.904417]        el0_svc_compat_handler+0x1c/0x24
  84 [   87.909289]        el0_svc_compat+0x8/0x18
  85 [   87.913378]
  86 [   87.913378] other info that might help us debug this:
  87 [   87.913378]
  88 [   87.921374]  Possible unsafe locking scenario:
  89 [   87.921374]
  90 [   87.927286]        CPU0                    CPU1
  91 [   87.931808]        ----                    ----
  92 [   87.936331]   lock(pwm_lock);
  93 [   87.939293]                                lock(kn->count#58);
  94 [   87.945120]                                lock(pwm_lock);
  95 [   87.950599]   lock(kn->count#58);
  96 [   87.953908]
  97 [   87.953908]  *** DEADLOCK ***
  98 [   87.953908]
  99 [   87.959821] 4 locks held by bash/2986:
 100 [   87.963563]  #0: 00000000ace7bc30 (sb_writers#6){.+.+}, at: vfs_write+0x188/0x19c
 101 [   87.971044]  #1: 00000000287991b2 (&of->mutex){+.+.}, at: kernfs_fop_write+0xb4/0x1e8
 102 [   87.978872]  #2: 00000000f739d016 (&dev->mutex){....}, at: device_release_driver_internal+0x40/0x21c
 103 [   87.988001]  #3: 000000006313b17c (pwm_lock){+.+.}, at: pwmchip_remove+0x28/0x13c
 104 [   87.995481]
 105 [   87.995481] stack backtrace:
 106 [   87.999836] CPU: 0 PID: 2986 Comm: bash Not tainted 5.0.0 #7
 107 [   88.005489] Hardware name: Renesas Salvator-X board based on r8a7795 ES1.x (DT)
 108 [   88.012791] Call trace:
 109 [   88.015235]  dump_backtrace+0x0/0x190
 110 [   88.018891]  show_stack+0x14/0x1c
 111 [   88.022204]  dump_stack+0xb0/0xec
 112 [   88.025514]  print_circular_bug.isra.32+0x1d0/0x2e0
 113 [   88.030385]  __lock_acquire+0x1318/0x1864
 114 [   88.034388]  lock_acquire+0xc4/0x22c
 115 [   88.037958]  __kernfs_remove+0x258/0x2c4
 116 [   88.041874]  kernfs_remove_by_name_ns+0x50/0xa0
 117 [   88.046398]  remove_files.isra.1+0x38/0x78
 118 [   88.050487]  sysfs_remove_group+0x48/0x98
 119 [   88.054490]  sysfs_remove_groups+0x34/0x4c
 120 [   88.058580]  device_remove_attrs+0x6c/0x7c
 121 [   88.062671]  device_del+0x11c/0x33c
 122 [   88.066154]  device_unregister+0x14/0x2c
 123 [   88.070070]  pwmchip_sysfs_unexport+0x40/0x4c
 124 [   88.074421]  pwmchip_remove+0xf4/0x13c
 125 [   88.078163]  rcar_pwm_remove+0x28/0x34
 126 [   88.081906]  platform_drv_remove+0x24/0x64
 127 [   88.085996]  device_release_driver_internal+0x18c/0x21c
 128 [   88.091215]  device_release_driver+0x14/0x1c
 129 [   88.095478]  unbind_store+0xe0/0x124
 130 [   88.099048]  drv_attr_store+0x20/0x30
 131 [   88.102704]  sysfs_kf_write+0x54/0x64
 132 [   88.106359]  kernfs_fop_write+0xe4/0x1e8
 133 [   88.110275]  __vfs_write+0x40/0x184
 134 [   88.113757]  vfs_write+0xa8/0x19c
 135 [   88.117065]  ksys_write+0x58/0xbc
 136 [   88.120374]  __arm64_sys_write+0x18/0x20
 137 [   88.124291]  el0_svc_common+0xd0/0x124
 138 [   88.128034]  el0_svc_compat_handler+0x1c/0x24
 139 [   88.132384]  el0_svc_compat+0x8/0x18
 140
 141 The sysfs unexport in pwmchip_remove() is completely asymmetric
 142 to what we do in pwmchip_add_with_polarity() and commit 0733424c9ba9
 143 ("pwm: Unexport children before chip removal") is a strong indication
 144 that this was wrong to begin with. We should just move
 145 pwmchip_sysfs_unexport() where it belongs, which is right after
 146 pwmchip_sysfs_unexport_children(). In that case, we do not need
 147 separate functions anymore either.
 148
 149 We also really want to remove sysfs irrespective of whether or not
 150 the chip will be removed as a result of pwmchip_remove(). We can only
 151 assume that the driver will be gone after that, so we shouldn't leave
 152 any dangling sysfs files around.
 153
 154 This warning disappears if we move pwmchip_sysfs_unexport() to
 155 the top of pwmchip_remove(), pwmchip_sysfs_unexport_children().
 156 That way it is also outside of the pwm_lock section, which indeed
 157 doesn't seem to be needed.
 158
 159 Moving the pwmchip_sysfs_export() call outside of that section also
 160 seems fine and it'd be perfectly symmetric with pwmchip_remove() again.
 161
 162 So, this patch fixes them.
 163
 164 Signed-off-by: Phong Hoang <phong.hoang.wz@renesas.com>
 165 [shimoda: revise the commit log and code]
 166 Fixes: 76abbdde2d95 ("pwm: Add sysfs interface")
 167 Fixes: 0733424c9ba9 ("pwm: Unexport children before chip removal")
 168 Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
 169 Tested-by: Hoan Nguyen An <na-hoan@jinso.co.jp>
 170 Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
 171 Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
 172 Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
 173 Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
 174 Signed-off-by: Sasha Levin <sashal@kernel.org>
 175 ---
 176  drivers/pwm/core.c  | 10 +++++-----
 177  drivers/pwm/sysfs.c | 14 +-------------
 178  include/linux/pwm.h |  5 -----
 179  3 files changed, 6 insertions(+), 23 deletions(-)
 180
 181 diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
 182 index 1581f6ab1b1f..c45e5719ba17 100644
 183 --- a/drivers/pwm/core.c
 184 +++ b/drivers/pwm/core.c
 185 @@ -311,10 +311,12 @@ int pwmchip_add_with_polarity(struct pwm_chip *chip,
 186         if (IS_ENABLED(CONFIG_OF))
 187                 of_pwmchip_add(chip);
 188
 189 -       pwmchip_sysfs_export(chip);
 190 -
 191  out:
 192         mutex_unlock(&pwm_lock);
 193 +
 194 +       if (!ret)
 195 +               pwmchip_sysfs_export(chip);
 196 +
 197         return ret;
 198  }
 199  EXPORT_SYMBOL_GPL(pwmchip_add_with_polarity);
 200 @@ -348,7 +350,7 @@ int pwmchip_remove(struct pwm_chip *chip)
 201         unsigned int i;
 202         int ret = 0;
 203
 204 -       pwmchip_sysfs_unexport_children(chip);
 205 +       pwmchip_sysfs_unexport(chip);
 206
 207         mutex_lock(&pwm_lock);
 208
 209 @@ -368,8 +370,6 @@ int pwmchip_remove(struct pwm_chip *chip)
 210
 211         free_pwms(chip);
 212
 213 -       pwmchip_sysfs_unexport(chip);
 214 -
 215  out:
 216         mutex_unlock(&pwm_lock);
 217         return ret;
 218 diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c
 219 index 7c71cdb8a9d8..1c64fd8e9234 100644
 220 --- a/drivers/pwm/sysfs.c
 221 +++ b/drivers/pwm/sysfs.c
 222 @@ -399,19 +399,6 @@ void pwmchip_sysfs_export(struct pwm_chip *chip)
 223  }
 224
 225  void pwmchip_sysfs_unexport(struct pwm_chip *chip)
 226 -{
 227 -       struct device *parent;
 228 -
 229 -       parent = class_find_device(&pwm_class, NULL, chip,
 230 -                                  pwmchip_sysfs_match);
 231 -       if (parent) {
 232 -               /* for class_find_device() */
 233 -               put_device(parent);
 234 -               device_unregister(parent);
 235 -       }
 236 -}
 237 -
 238 -void pwmchip_sysfs_unexport_children(struct pwm_chip *chip)
 239  {
 240         struct device *parent;
 241         unsigned int i;
 242 @@ -429,6 +416,7 @@ void pwmchip_sysfs_unexport_children(struct pwm_chip *chip)
 243         }
 244
 245         put_device(parent);
 246 +       device_unregister(parent);
 247  }
 248
 249  static int __init pwm_sysfs_init(void)
 250 diff --git a/include/linux/pwm.h b/include/linux/pwm.h
 251 index 56518adc31dd..bd7d611d63e9 100644
 252 --- a/include/linux/pwm.h
 253 +++ b/include/linux/pwm.h
 254 @@ -639,7 +639,6 @@ static inline void pwm_remove_table(struct pwm_lookup *table, size_t num)
 255  #ifdef CONFIG_PWM_SYSFS
 256  void pwmchip_sysfs_export(struct pwm_chip *chip);
 257  void pwmchip_sysfs_unexport(struct pwm_chip *chip);
 258 -void pwmchip_sysfs_unexport_children(struct pwm_chip *chip);
 259  #else
 260  static inline void pwmchip_sysfs_export(struct pwm_chip *chip)
 261  {
 262 @@ -648,10 +647,6 @@ static inline void pwmchip_sysfs_export(struct pwm_chip *chip)
 263  static inline void pwmchip_sysfs_unexport(struct pwm_chip *chip)
 264  {
 265  }
 266 -
 267 -static inline void pwmchip_sysfs_unexport_children(struct pwm_chip *chip)
 268 -{
 269 -}
 270  #endif /* CONFIG_PWM_SYSFS */
 271
 272  #endif /* __LINUX_PWM_H */
 273 --
 274 2.20.1
 275