From f3c74b38a55aefe1004200d15a83f109b510068c Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Sat, 20 Apr 2019 13:27:51 +0200 Subject: RAS/CEC: Fix binary search function Switch to using Donald Knuth's binary search algorithm (The Art of Computer Programming, vol. 3, section 6.2.1). This should've been done from the very beginning but the author must've been smoking something very potent at the time. The problem with the current one was that it would return the wrong element index in certain situations: https://lkml.kernel.org/r/CAM_iQpVd02zkVJ846cj-Fg1yUNuz6tY5q1Vpj4LrXmE06dPYYg@mail.gmail.com and the noodling code after the loop was fishy at best. So switch to using Knuth's binary search. The final result is much cleaner and straightforward. Fixes: 011d82611172 ("RAS: Add a Corrected Errors Collector") Reported-by: Cong Wang Signed-off-by: Borislav Petkov Cc: Tony Luck Cc: linux-edac Cc: --- drivers/ras/cec.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-) diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c index 88e4f3ff0cb8..dbfe3e61d2c2 100644 --- a/drivers/ras/cec.c +++ b/drivers/ras/cec.c @@ -183,32 +183,38 @@ static void cec_timer_fn(struct timer_list *unused) */ static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to) { + int min = 0, max = ca->n - 1; u64 this_pfn; - int min = 0, max = ca->n; - while (min < max) { - int tmp = (max + min) >> 1; + while (min <= max) { + int i = (min + max) >> 1; - this_pfn = PFN(ca->array[tmp]); + this_pfn = PFN(ca->array[i]); if (this_pfn < pfn) - min = tmp + 1; + min = i + 1; else if (this_pfn > pfn) - max = tmp; - else { - min = tmp; - break; + max = i - 1; + else if (this_pfn == pfn) { + if (to) + *to = i; + + return i; } } + /* + * When the loop terminates without finding @pfn, min has the index of + * the element slot where the new @pfn should be inserted. The loop + * terminates when min > max, which means the min index points to the + * bigger element while the max index to the smaller element, in-between + * which the new @pfn belongs to. + * + * For more details, see exercise 1, Section 6.2.1 in TAOCP, vol. 3. + */ if (to) *to = min; - this_pfn = PFN(ca->array[min]); - - if (this_pfn == pfn) - return min; - return -ENOKEY; } -- cgit v1.2.3 From 0ade0b6240c4853cf9725924c46c10f4251639d7 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Tue, 16 Apr 2019 14:33:51 -0700 Subject: RAS/CEC: Convert the timer callback to a workqueue cec_timer_fn() is a timer callback which reads ce_arr.array[] and updates its decay values. However, it runs in interrupt context and the mutex protection the CEC uses for that array, is inadequate. Convert the used timer to a workqueue to keep the tasks the CEC performs preemptible and thus low-prio. [ bp: Rewrite commit message. s/timer/decay/gi to make it agnostic as to what facility is used. ] Fixes: 011d82611172 ("RAS: Add a Corrected Errors Collector") Signed-off-by: Cong Wang Signed-off-by: Borislav Petkov Cc: Thomas Gleixner Cc: Tony Luck Cc: linux-edac Cc: Link: https://lkml.kernel.org/r/20190416213351.28999-2-xiyou.wangcong@gmail.com --- drivers/ras/cec.c | 46 ++++++++++++++++++++++------------------------ 1 file changed, 22 insertions(+), 24 deletions(-) diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c index dbfe3e61d2c2..673f8a128397 100644 --- a/drivers/ras/cec.c +++ b/drivers/ras/cec.c @@ -2,6 +2,7 @@ #include #include #include +#include #include @@ -123,16 +124,12 @@ static u64 dfs_pfn; /* Amount of errors after which we offline */ static unsigned int count_threshold = COUNT_MASK; -/* - * The timer "decays" element count each timer_interval which is 24hrs by - * default. - */ - -#define CEC_TIMER_DEFAULT_INTERVAL 24 * 60 * 60 /* 24 hrs */ -#define CEC_TIMER_MIN_INTERVAL 1 * 60 * 60 /* 1h */ -#define CEC_TIMER_MAX_INTERVAL 30 * 24 * 60 * 60 /* one month */ -static struct timer_list cec_timer; -static u64 timer_interval = CEC_TIMER_DEFAULT_INTERVAL; +/* Each element "decays" each decay_interval which is 24hrs by default. */ +#define CEC_DECAY_DEFAULT_INTERVAL 24 * 60 * 60 /* 24 hrs */ +#define CEC_DECAY_MIN_INTERVAL 1 * 60 * 60 /* 1h */ +#define CEC_DECAY_MAX_INTERVAL 30 * 24 * 60 * 60 /* one month */ +static struct delayed_work cec_work; +static u64 decay_interval = CEC_DECAY_DEFAULT_INTERVAL; /* * Decrement decay value. We're using DECAY_BITS bits to denote decay of an @@ -160,20 +157,21 @@ static void do_spring_cleaning(struct ce_array *ca) /* * @interval in seconds */ -static void cec_mod_timer(struct timer_list *t, unsigned long interval) +static void cec_mod_work(unsigned long interval) { unsigned long iv; - iv = interval * HZ + jiffies; - - mod_timer(t, round_jiffies(iv)); + iv = interval * HZ; + mod_delayed_work(system_wq, &cec_work, round_jiffies(iv)); } -static void cec_timer_fn(struct timer_list *unused) +static void cec_work_fn(struct work_struct *work) { + mutex_lock(&ce_mutex); do_spring_cleaning(&ce_arr); + mutex_unlock(&ce_mutex); - cec_mod_timer(&cec_timer, timer_interval); + cec_mod_work(decay_interval); } /* @@ -380,15 +378,15 @@ static int decay_interval_set(void *data, u64 val) { *(u64 *)data = val; - if (val < CEC_TIMER_MIN_INTERVAL) + if (val < CEC_DECAY_MIN_INTERVAL) return -EINVAL; - if (val > CEC_TIMER_MAX_INTERVAL) + if (val > CEC_DECAY_MAX_INTERVAL) return -EINVAL; - timer_interval = val; + decay_interval = val; - cec_mod_timer(&cec_timer, timer_interval); + cec_mod_work(decay_interval); return 0; } DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n"); @@ -432,7 +430,7 @@ static int array_dump(struct seq_file *m, void *v) seq_printf(m, "Flags: 0x%x\n", ca->flags); - seq_printf(m, "Timer interval: %lld seconds\n", timer_interval); + seq_printf(m, "Decay interval: %lld seconds\n", decay_interval); seq_printf(m, "Decays: %lld\n", ca->decays_done); seq_printf(m, "Action threshold: %d\n", count_threshold); @@ -478,7 +476,7 @@ static int __init create_debugfs_nodes(void) } decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d, - &timer_interval, &decay_interval_ops); + &decay_interval, &decay_interval_ops); if (!decay) { pr_warn("Error creating decay_interval debugfs node!\n"); goto err; @@ -514,8 +512,8 @@ void __init cec_init(void) if (create_debugfs_nodes()) return; - timer_setup(&cec_timer, cec_timer_fn, 0); - cec_mod_timer(&cec_timer, CEC_TIMER_DEFAULT_INTERVAL); + INIT_DELAYED_WORK(&cec_work, cec_work_fn); + schedule_delayed_work(&cec_work, CEC_DECAY_DEFAULT_INTERVAL); pr_info("Correctable Errors collector initialized.\n"); } -- cgit v1.2.3