From: Phong Hoang <[email protected]>
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
This warning occurs because pwmchip_remove still keeps pwm_lock
when removing sysfs. That's why it leads to that conflict.
Hence, this patch unlocks pwm_lock before removing sysfs.
Also, pwmchip_sysfs_export() doesn't seem to need the pwm_lock
held so that to achieve consistance between export and
unexport this patch also modifies it.
Signed-off-by: Phong Hoang <[email protected]>
[shimoda: revise the commit log and code]
Fixes: 76abbdde2d95 ("pwm: Add sysfs interface")
Signed-off-by: Yoshihiro Shimoda <[email protected]>
Tested-by: Hoan Nguyen An <[email protected]>
---
drivers/pwm/core.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 1581f6a..2fdd6611 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);
@@ -368,10 +370,12 @@ int pwmchip_remove(struct pwm_chip *chip)
free_pwms(chip);
- pwmchip_sysfs_unexport(chip);
-
out:
mutex_unlock(&pwm_lock);
+
+ if (!ret)
+ pwmchip_sysfs_unexport(chip);
+
return ret;
}
EXPORT_SYMBOL_GPL(pwmchip_remove);
--
2.7.4
