From 3ffb7c45d193c771d7fc7722be0a45bc196f25f9 Mon Sep 17 00:00:00 2001 From: Kent Gibson Date: Wed, 14 Oct 2020 14:29:21 +0800 Subject: [PATCH] gpiolib: cdev: document that line eflags are shared The line.eflags field is shared so document this fact and highlight it throughout using READ_ONCE() and WRITE_ONCE() accessors. Also use a local copy of the eflags in edge_irq_thread() to ensure consistent control flow even if eflags changes. This is only a defensive measure as edge_irq_thread() is currently disabled when the eflags are changed. Signed-off-by: Kent Gibson Signed-off-by: Bartosz Golaszewski --- drivers/gpio/gpiolib-cdev.c | 32 +++++++++++++++++++++----------- 1 file changed, 21 insertions(+), 11 deletions(-) diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c index e9faeaf65d14..519ecfa40a3b 100644 --- a/drivers/gpio/gpiolib-cdev.c +++ b/drivers/gpio/gpiolib-cdev.c @@ -428,6 +428,12 @@ struct line { */ struct linereq *req; unsigned int irq; + /* + * eflags is set by edge_detector_setup(), edge_detector_stop() and + * edge_detector_update(), which are themselves mutually exclusive, + * and is accessed by edge_irq_thread() and debounce_work_func(), + * which can both live with a slightly stale value. + */ u64 eflags; /* * timestamp_ns and req_seqno are accessed only by @@ -534,6 +540,7 @@ static irqreturn_t edge_irq_thread(int irq, void *p) struct line *line = p; struct linereq *lr = line->req; struct gpio_v2_line_event le; + u64 eflags; /* Do not leak kernel stack to userspace */ memset(&le, 0, sizeof(le)); @@ -552,8 +559,9 @@ static irqreturn_t edge_irq_thread(int irq, void *p) } line->timestamp_ns = 0; - if (line->eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING | - GPIO_V2_LINE_FLAG_EDGE_FALLING)) { + eflags = READ_ONCE(line->eflags); + if (eflags == (GPIO_V2_LINE_FLAG_EDGE_RISING | + GPIO_V2_LINE_FLAG_EDGE_FALLING)) { int level = gpiod_get_value_cansleep(line->desc); if (level) @@ -562,10 +570,10 @@ static irqreturn_t edge_irq_thread(int irq, void *p) else /* Emit high-to-low event */ le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE; - } else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) { + } else if (eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) { /* Emit low-to-high event */ le.id = GPIO_V2_LINE_EVENT_RISING_EDGE; - } else if (line->eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) { + } else if (eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) { /* Emit high-to-low event */ le.id = GPIO_V2_LINE_EVENT_FALLING_EDGE; } else { @@ -634,6 +642,7 @@ static void debounce_work_func(struct work_struct *work) struct line *line = container_of(work, struct line, work.work); struct linereq *lr; int level; + u64 eflags; level = gpiod_get_raw_value_cansleep(line->desc); if (level < 0) { @@ -647,7 +656,8 @@ static void debounce_work_func(struct work_struct *work) WRITE_ONCE(line->level, level); /* -- edge detection -- */ - if (!line->eflags) + eflags = READ_ONCE(line->eflags); + if (!eflags) return; /* switch from physical level to logical - if they differ */ @@ -655,8 +665,8 @@ static void debounce_work_func(struct work_struct *work) level = !level; /* ignore edges that are not being monitored */ - if (((line->eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) && !level) || - ((line->eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) && level)) + if (((eflags == GPIO_V2_LINE_FLAG_EDGE_RISING) && !level) || + ((eflags == GPIO_V2_LINE_FLAG_EDGE_FALLING) && level)) return; /* Do not leak kernel stack to userspace */ @@ -755,7 +765,7 @@ static void edge_detector_stop(struct line *line) cancel_delayed_work_sync(&line->work); WRITE_ONCE(line->sw_debounced, 0); - line->eflags = 0; + WRITE_ONCE(line->eflags, 0); /* do not change line->level - see comment in debounced_value() */ } @@ -774,7 +784,7 @@ static int edge_detector_setup(struct line *line, if (ret) return ret; } - line->eflags = eflags; + WRITE_ONCE(line->eflags, eflags); if (gpio_v2_line_config_debounced(lc, line_idx)) { debounce_period_us = gpio_v2_line_config_debounce_period(lc, line_idx); ret = debounce_setup(line, debounce_period_us); @@ -817,13 +827,13 @@ static int edge_detector_update(struct line *line, unsigned int debounce_period_us = gpio_v2_line_config_debounce_period(lc, line_idx); - if ((line->eflags == eflags) && !polarity_change && + if ((READ_ONCE(line->eflags) == eflags) && !polarity_change && (READ_ONCE(line->desc->debounce_period_us) == debounce_period_us)) return 0; /* sw debounced and still will be...*/ if (debounce_period_us && READ_ONCE(line->sw_debounced)) { - line->eflags = eflags; + WRITE_ONCE(line->eflags, eflags); WRITE_ONCE(line->desc->debounce_period_us, debounce_period_us); return 0; }