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Subject[PATCH 2/2] ras: close the race condition with timer
Date
cec_timer_fn() is a timer callback which reads ce_arr.array[]
and updates its decay values. Elements could be added to or
removed from this global array in parallel, although the array
itself will not grow or shrink. del_lru_elem_unlocked() uses
FULL_COUNT() as a key to find a right element to remove,
which could be affected by the parallel timer.

Fix this by converting the mutex to a spinlock and holding it
inside the timer.

Fixes: 011d82611172 ("RAS: Add a Corrected Errors Collector")
Cc: Tony Luck <tony.luck@intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
drivers/ras/cec.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c
index 61332c9aab5a..a82c9d08d47a 100644
--- a/drivers/ras/cec.c
+++ b/drivers/ras/cec.c
@@ -117,7 +117,7 @@ static struct ce_array {
};
} ce_arr;

-static DEFINE_MUTEX(ce_mutex);
+static DEFINE_SPINLOCK(ce_lock);
static u64 dfs_pfn;

/* Amount of errors after which we offline */
@@ -171,7 +171,9 @@ static void cec_mod_timer(struct timer_list *t, unsigned long interval)

static void cec_timer_fn(struct timer_list *unused)
{
+ spin_lock(&ce_lock);
do_spring_cleaning(&ce_arr);
+ spin_unlock(&ce_lock);

cec_mod_timer(&cec_timer, timer_interval);
}
@@ -265,9 +267,9 @@ static u64 __maybe_unused del_lru_elem(void)
if (!ca->n)
return 0;

- mutex_lock(&ce_mutex);
+ spin_lock_bh(&ce_lock);
pfn = del_lru_elem_unlocked(ca);
- mutex_unlock(&ce_mutex);
+ spin_unlock_bh(&ce_lock);

return pfn;
}
@@ -288,7 +290,7 @@ int cec_add_elem(u64 pfn)

ca->ces_entered++;

- mutex_lock(&ce_mutex);
+ spin_lock_bh(&ce_lock);

if (ca->n == MAX_ELEMS)
WARN_ON(!del_lru_elem_unlocked(ca));
@@ -349,7 +351,7 @@ int cec_add_elem(u64 pfn)
do_spring_cleaning(ca);

unlock:
- mutex_unlock(&ce_mutex);
+ spin_unlock_bh(&ce_lock);

return ret;
}
@@ -406,7 +408,7 @@ static int array_dump(struct seq_file *m, void *v)
u64 prev = 0;
int i;

- mutex_lock(&ce_mutex);
+ spin_lock_bh(&ce_lock);

seq_printf(m, "{ n: %d\n", ca->n);
for (i = 0; i < ca->n; i++) {
@@ -431,7 +433,7 @@ static int array_dump(struct seq_file *m, void *v)

seq_printf(m, "Action threshold: %d\n", count_threshold);

- mutex_unlock(&ce_mutex);
+ spin_unlock_bh(&ce_lock);

return 0;
}
--
2.20.1
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