[BUG] Possible sleep-in-atomic-context bugs involving regmap_lock_mutex()

[Jia-Ju Bai]

Hello,

My static tool DSAC reports many sleep-in-atomic-context bugs involving 
regmap_lock_mutex(), so I wonder whether this function is possible to be 
executed in atomic context.

Here are some example bugs and their call paths in Linux-4.16 (from 
bottom to top, and [FUNC_PTR] means that there is a function pointer call):

[FUNC] mutex_lock_nested
drivers/base/regmap/regmap.c, 468:
    mutex_lock_nested in regmap_lock_mutex
drivers/base/regmap/regmap.c, 2503:
    [FUNC_PTR]regmap_lock_mutex in regmap_read
drivers/clk/clk-aspeed.c, 215:
    regmap_read in aspeed_clk_is_enabled
drivers/clk/clk-aspeed.c, 230:
    aspeed_clk_is_enabled in aspeed_clk_enable
drivers/clk/clk-aspeed.c, 228:
    _raw_spin_lock_irqsave in aspeed_clk_enable

[FUNC] mutex_lock_nested
drivers/base/regmap/regmap.c, 468:
    mutex_lock_nested in regmap_lock_mutex
drivers/base/regmap/regmap.c, 2821:
    [FUNC_PTR]regmap_lock_mutex in regmap_update_bits_base
drivers/clk/clk-aspeed.c, 270:
    regmap_update_bits_base in aspeed_clk_disable
drivers/clk/clk-aspeed.c, 267:
    _raw_spin_lock_irqsave in aspeed_clk_disable

[FUNC] mutex_lock_nested
drivers/base/regmap/regmap.c, 468:
    mutex_lock_nested in regmap_lock_mutex
drivers/base/regmap/regmap.c, 2503:
    [FUNC_PTR]regmap_lock_mutex in regmap_read
drivers/char/ipmi/bt-bmc.c, 385:
    regmap_read in bt_bmc_irq

[FUNC] mutex_lock_nested
drivers/base/regmap/regmap.c, 468:
    mutex_lock_nested in regmap_lock_mutex
drivers/base/regmap/regmap.c, 2821:
    [FUNC_PTR]regmap_lock_mutex in regmap_update_bits_base
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c, 213:
    regmap_update_bits_base in hdmi_modb
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c, 429:
    hdmi_modb in hdmi_set_cts_n
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c, 527:
    hdmi_set_cts_n in hdmi_set_clk_regenerator
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c, 524:
    spin_lock_irq in hdmi_set_clk_regenerator

[FUNC] mutex_lock_nested
drivers/base/regmap/regmap.c, 468:
    mutex_lock_nested in regmap_lock_mutex
drivers/base/regmap/regmap.c, 2503:
    [FUNC_PTR]regmap_lock_mutex in regmap_read
drivers/media/platform/atmel/atmel-isc.c, 1603:
    regmap_read in isc_interrupt (interrupt handler)

I find the code about the assignment of regmap_lock_mutex():
        if ((bus && bus->fast_io) ||
            config->fast_io) {
            spin_lock_init(&map->spinlock);
            map->lock = regmap_lock_spinlock;
            map->unlock = regmap_unlock_spinlock;
            lockdep_set_class_and_name(&map->spinlock,
                           lock_key, lock_name);
        } else {
            mutex_init(&map->mutex);
            map->lock = regmap_lock_mutex;
            map->unlock = regmap_unlock_mutex;
            lockdep_set_class_and_name(&map->mutex,
                           lock_key, lock_name);
        }

But after reading the code, I cannot find the relationship between the 
if condition and atomic context.

I am looking forward to your reply, thanks in advance :)


Best wishes,
Jia-Ju Bai