Re: [PATCH RFC] regmap: maple: Switch to use irq-safe locking

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, Aug 14, 2024 at 01:20:21AM +0300, Cristian Ciocaltea wrote:
> Commit 3d59c22bbb8d ("drm/rockchip: vop2: Convert to use maple tree
> register cache") enabled the use of maple tree register cache in
> Rockchip VOP2 driver.  However, building the kernel with lockdep support
> indicates locking rules violation when trying to unload the rockchipdrm
> module:
> 
> [ 48.360258] ========================================================
> [ 48.360829] WARNING: possible irq lock inversion dependency detected
> [ 48.361400] 6.11.0-rc1 #40 Not tainted
> [ 48.361743] --------------------------------------------------------
> [ 48.362311] modprobe/685 just changed the state of lock:
> [ 48.362790] ffff0000087fa798 (&mt->ma_lock){+...}-{2:2}, at: regcache_maple_exit+0x6c/0xe0
> [ 48.363554] but this lock was taken by another, HARDIRQ-safe lock in the past:
> [ 48.364212]  (rockchip_drm_vop2:3114:(&vop2_regmap_config)->lock){-.-.}-{2:2}
> [ 48.364226]
> 
>              and interrupts could create inverse lock ordering between them.
> 
> [ 48.365874]
>              other info that might help us debug this:
> [ 48.366460]  Possible interrupt unsafe locking scenario:
> 
> [ 48.367069]        CPU0                    CPU1
> [ 48.367478]        ----                    ----
> [ 48.367889]   lock(&mt->ma_lock);
> [ 48.368197]                                local_irq_disable();
> [ 48.368729]                                lock(rockchip_drm_vop2:3114:(&vop2_regmap_config)->lock);
> [ 48.369551]                                lock(&mt->ma_lock);
> [ 48.370081]   <Interrupt>
> [ 48.370336]     lock(rockchip_drm_vop2:3114:(&vop2_regmap_config)->lock);
> [ 48.370957]
>                 *** DEADLOCK ***
> 
> [ 48.371489] 2 locks held by modprobe/685:
> [ 48.371854]  #0: ffff0000018898f8 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0x54/0x210
> [ 48.372739]  #1: ffff800081c6ca80 (component_mutex){+.+.}-{3:3}, at: component_del+0x38/0x158
> [ 48.373522]
>                the shortest dependencies between 2nd lock and 1st lock:
> [ 48.374235]  -> (rockchip_drm_vop2:3114:(&vop2_regmap_config)->lock){-.-.}-{2:2} {
> [ 48.374941]     IN-HARDIRQ-W at:
> [ 48.375239]                       lock_acquire+0x1d4/0x320
> [ 48.375739]                       _raw_spin_lock_irqsave+0x6c/0x98
> [ 48.376300]                       regmap_lock_spinlock+0x20/0x40
> [ 48.376845]                       regmap_read+0x44/0x88
> [ 48.377321]                       vop2_isr+0x90/0x290 [rockchipdrm]
> [ 48.377919]                       __handle_irq_event_percpu+0x114/0x2b0
> [ 48.378519]                       handle_irq_event+0x54/0xb8
> [ 48.379032]                       handle_fasteoi_irq+0x158/0x228
> [ 48.379577]                       generic_handle_domain_irq+0x34/0x58
> [ 48.380160]                       gic_handle_irq+0xa4/0x114
> 
> [...]
> 
> [ 48.466666] -> (&mt->ma_lock){+...}-{2:2} {
> [ 48.467066]    HARDIRQ-ON-W at:
> [ 48.467360]                     lock_acquire+0x1d4/0x320
> [ 48.467849]                     _raw_spin_lock+0x50/0x70
> [ 48.468337]                     regcache_maple_exit+0x6c/0xe0
> [ 48.468864]                     regcache_exit+0x8c/0xa8
> [ 48.469344]                     regmap_exit+0x24/0x160
> [ 48.469815]                     devm_regmap_release+0x1c/0x28
> [ 48.470339]                     release_nodes+0x68/0xa8
> [ 48.470818]                     devres_release_group+0x120/0x180
> [ 48.471364]                     component_unbind+0x54/0x70
> [ 48.471867]                     component_unbind_all+0xb0/0xe8
> [ 48.472400]                     rockchip_drm_unbind+0x44/0x80 [rockchipdrm]
> [ 48.473059]                     component_del+0xc8/0x158
> [ 48.473545]                     dw_hdmi_rockchip_remove+0x28/0x40 [rockchipdrm]
> 
> The problem is that the regmap lock could be taken by an IRQ context,
> interrupting the irq-unsafe maple tree lock, which may result in a lock
> inversion deadlock scenario.
> 
> Switch to use irq-safe locking in the maple tree register cache.
> 
> Fixes: f033c26de5a5 ("regmap: Add maple tree based register cache")
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
> ---
>  drivers/base/regmap/regcache-maple.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
> 

Hi,

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