| Message ID | 20241209074659.1442898-1-e.shatokhin@yadro.com |
|---|---|
| State | New |
| Headers | show |
| Series | pinctrl: mcp23s08: Fix sleeping in atomic context due to regmap locking | expand |
On Mon, Dec 9, 2024 at 8:47 AM Evgenii Shatokhin <e.shatokhin@yadro.com> wrote: > If a device uses MCP23xxx IO expander to receive IRQs, the following > bug can happen: > > BUG: sleeping function called from invalid context > at kernel/locking/mutex.c:283 > in_atomic(): 1, irqs_disabled(): 1, non_block: 0, ... > preempt_count: 1, expected: 0 > ... > Call Trace: > ... > __might_resched+0x104/0x10e > __might_sleep+0x3e/0x62 > mutex_lock+0x20/0x4c > regmap_lock_mutex+0x10/0x18 > regmap_update_bits_base+0x2c/0x66 > mcp23s08_irq_set_type+0x1ae/0x1d6 > __irq_set_trigger+0x56/0x172 > __setup_irq+0x1e6/0x646 > request_threaded_irq+0xb6/0x160 > ... > > We observed the problem while experimenting with a touchscreen driver which > used MCP23017 IO expander (I2C). > > The regmap in the pinctrl-mcp23s08 driver uses a mutex for protection from > concurrent accesses, which is the default for regmaps without .fast_io, > .disable_locking, etc. > > mcp23s08_irq_set_type() calls regmap_update_bits_base(), and the latter > locks the mutex. > > However, __setup_irq() locks desc->lock spinlock before calling these > functions. As a result, the system tries to lock the mutex whole holding > the spinlock. > > It seems, the internal regmap locks are not needed in this driver at all. > mcp->lock seems to protect the regmap from concurrent accesses already, > except, probably, in mcp_pinconf_get/set. > > mcp23s08_irq_set_type() and mcp23s08_irq_mask/unmask() are called under > chip_bus_lock(), which calls mcp23s08_irq_bus_lock(). The latter takes > mcp->lock and enables regmap caching, so that the potentially slow I2C > accesses are deferred until chip_bus_unlock(). > > The accesses to the regmap from mcp23s08_probe_one() do not need additional > locking. > > In all remaining places where the regmap is accessed, except > mcp_pinconf_get/set(), the driver already takes mcp->lock. > > This patch adds locking in mcp_pinconf_get/set() and disables internal > locking in the regmap config. Among other things, it fixes the sleeping > in atomic context described above. > > Fixes: 8f38910ba4f6 ("pinctrl: mcp23s08: switch to regmap caching") > Cc: stable@vger.kernel.org > Signed-off-by: Evgenii Shatokhin <e.shatokhin@yadro.com> Excellent analysis, patch applied! Yours, Linus Walleij
diff --git a/drivers/pinctrl/pinctrl-mcp23s08.c b/drivers/pinctrl/pinctrl-mcp23s08.c index d66c3a3e8429..b96e6368a956 100644 --- a/drivers/pinctrl/pinctrl-mcp23s08.c +++ b/drivers/pinctrl/pinctrl-mcp23s08.c @@ -86,6 +86,7 @@ const struct regmap_config mcp23x08_regmap = { .num_reg_defaults = ARRAY_SIZE(mcp23x08_defaults), .cache_type = REGCACHE_FLAT, .max_register = MCP_OLAT, + .disable_locking = true, /* mcp->lock protects the regmap */ }; EXPORT_SYMBOL_GPL(mcp23x08_regmap); @@ -132,6 +133,7 @@ const struct regmap_config mcp23x17_regmap = { .num_reg_defaults = ARRAY_SIZE(mcp23x17_defaults), .cache_type = REGCACHE_FLAT, .val_format_endian = REGMAP_ENDIAN_LITTLE, + .disable_locking = true, /* mcp->lock protects the regmap */ }; EXPORT_SYMBOL_GPL(mcp23x17_regmap); @@ -228,7 +230,9 @@ static int mcp_pinconf_get(struct pinctrl_dev *pctldev, unsigned int pin, switch (param) { case PIN_CONFIG_BIAS_PULL_UP: + mutex_lock(&mcp->lock); ret = mcp_read(mcp, MCP_GPPU, &data); + mutex_unlock(&mcp->lock); if (ret < 0) return ret; status = (data & BIT(pin)) ? 1 : 0; @@ -257,7 +261,9 @@ static int mcp_pinconf_set(struct pinctrl_dev *pctldev, unsigned int pin, switch (param) { case PIN_CONFIG_BIAS_PULL_UP: + mutex_lock(&mcp->lock); ret = mcp_set_bit(mcp, MCP_GPPU, pin, arg); + mutex_unlock(&mcp->lock); break; default: dev_dbg(mcp->dev, "Invalid config param %04x\n", param);
If a device uses MCP23xxx IO expander to receive IRQs, the following bug can happen: BUG: sleeping function called from invalid context at kernel/locking/mutex.c:283 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, ... preempt_count: 1, expected: 0 ... Call Trace: ... __might_resched+0x104/0x10e __might_sleep+0x3e/0x62 mutex_lock+0x20/0x4c regmap_lock_mutex+0x10/0x18 regmap_update_bits_base+0x2c/0x66 mcp23s08_irq_set_type+0x1ae/0x1d6 __irq_set_trigger+0x56/0x172 __setup_irq+0x1e6/0x646 request_threaded_irq+0xb6/0x160 ... We observed the problem while experimenting with a touchscreen driver which used MCP23017 IO expander (I2C). The regmap in the pinctrl-mcp23s08 driver uses a mutex for protection from concurrent accesses, which is the default for regmaps without .fast_io, .disable_locking, etc. mcp23s08_irq_set_type() calls regmap_update_bits_base(), and the latter locks the mutex. However, __setup_irq() locks desc->lock spinlock before calling these functions. As a result, the system tries to lock the mutex whole holding the spinlock. It seems, the internal regmap locks are not needed in this driver at all. mcp->lock seems to protect the regmap from concurrent accesses already, except, probably, in mcp_pinconf_get/set. mcp23s08_irq_set_type() and mcp23s08_irq_mask/unmask() are called under chip_bus_lock(), which calls mcp23s08_irq_bus_lock(). The latter takes mcp->lock and enables regmap caching, so that the potentially slow I2C accesses are deferred until chip_bus_unlock(). The accesses to the regmap from mcp23s08_probe_one() do not need additional locking. In all remaining places where the regmap is accessed, except mcp_pinconf_get/set(), the driver already takes mcp->lock. This patch adds locking in mcp_pinconf_get/set() and disables internal locking in the regmap config. Among other things, it fixes the sleeping in atomic context described above. Fixes: 8f38910ba4f6 ("pinctrl: mcp23s08: switch to regmap caching") Cc: stable@vger.kernel.org Signed-off-by: Evgenii Shatokhin <e.shatokhin@yadro.com> --- drivers/pinctrl/pinctrl-mcp23s08.c | 6 ++++++ 1 file changed, 6 insertions(+)