On Tue, Mar 19, 2019 at 07:40:08PM +0900, Yoshihiro Shimoda wrote: > 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(-) Applied, thanks! Thierry