On Tue, Mar 19, 2019 at 07:40:08PM +0900, Yoshihiro Shimoda wrote:
> From: Phong Hoang <phong.hoang.wz@xxxxxxxxxxx>
>
> 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 <phong.hoang.wz@xxxxxxxxxxx>
> [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 <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> Tested-by: Hoan Nguyen An <na-hoan@xxxxxxxxxxx>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxx/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
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