The patch 70bbeb29fab0 broke dm-delay seriously. It introduced the
following bugs:
* the function flush_worker_fn has no exit path - on unload, this function
will just loop and consume 100% CPU without any progress
* the wake-up mechanism in flush_worker_fn is racy - a wake up will be
missed if the process adds entries to the delayed_bios list just before
set_current_state(TASK_INTERRUPTIBLE)
* flush_delayed_bios_fast submits a bio while holding a global mutex; this
may deadlock if we have multiple stacked dm-delay devices and the
underlying device attempts to acquire the mutex too
* if the target constructor fails, it will call delay_dtr. delay_dtr would
attempt to free dc->timer_lock without it being initialized by the
constructor; if kthread allocation fails, delay_dtr would crash trying
to dereference dc->worker because it would ontain error code
This commit fixes these bugs.
Fixes: 70bbeb29fab0 ("dm delay: for short delays, use kthread instead of timers and wq")
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
drivers/md/dm-delay.c | 61 ++++++++++++++++++++++++++++----------------------
1 file changed, 35 insertions(+), 26 deletions(-)
Index: linux-2.6/drivers/md/dm-delay.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-delay.c 2023-11-17 14:57:26.000000000 +0100
+++ linux-2.6/drivers/md/dm-delay.c 2023-11-17 14:58:44.000000000 +0100
@@ -73,9 +73,23 @@ static inline bool delay_is_fast(struct
return !!dc->worker;
}
+static void flush_bios(struct bio *bio)
+{
+ struct bio *n;
+
+ while (bio) {
+ n = bio->bi_next;
+ bio->bi_next = NULL;
+ dm_submit_bio_remap(bio, NULL);
+ bio = n;
+ }
+}
+
static void flush_delayed_bios_fast(struct delay_c *dc, bool flush_all)
{
struct dm_delay_info *delayed, *next;
+ struct bio_list flush_bio_list;
+ bio_list_init(&flush_bio_list);
mutex_lock(&delayed_bios_lock);
list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) {
@@ -83,47 +97,42 @@ static void flush_delayed_bios_fast(stru
struct bio *bio = dm_bio_from_per_bio_data(delayed,
sizeof(struct dm_delay_info));
list_del(&delayed->list);
- dm_submit_bio_remap(bio, NULL);
+ bio_list_add(&flush_bio_list, bio);
delayed->class->ops--;
}
}
mutex_unlock(&delayed_bios_lock);
+
+ flush_bios(bio_list_get(&flush_bio_list));
}
static int flush_worker_fn(void *data)
{
struct delay_c *dc = data;
- while (1) {
+ while (!kthread_should_stop()) {
flush_delayed_bios_fast(dc, false);
+ mutex_lock(&delayed_bios_lock);
if (unlikely(list_empty(&dc->delayed_bios))) {
set_current_state(TASK_INTERRUPTIBLE);
+ mutex_unlock(&delayed_bios_lock);
schedule();
- } else
+ } else {
+ mutex_unlock(&delayed_bios_lock);
cond_resched();
+ }
}
return 0;
}
-static void flush_bios(struct bio *bio)
-{
- struct bio *n;
-
- while (bio) {
- n = bio->bi_next;
- bio->bi_next = NULL;
- dm_submit_bio_remap(bio, NULL);
- bio = n;
- }
-}
-
-static struct bio *flush_delayed_bios(struct delay_c *dc, bool flush_all)
+static void flush_delayed_bios(struct delay_c *dc, bool flush_all)
{
struct dm_delay_info *delayed, *next;
unsigned long next_expires = 0;
unsigned long start_timer = 0;
- struct bio_list flush_bios = { };
+ struct bio_list flush_bio_list;
+ bio_list_init(&flush_bio_list);
mutex_lock(&delayed_bios_lock);
list_for_each_entry_safe(delayed, next, &dc->delayed_bios, list) {
@@ -131,7 +140,7 @@ static struct bio *flush_delayed_bios(st
struct bio *bio = dm_bio_from_per_bio_data(delayed,
sizeof(struct dm_delay_info));
list_del(&delayed->list);
- bio_list_add(&flush_bios, bio);
+ bio_list_add(&flush_bio_list, bio);
delayed->class->ops--;
continue;
}
@@ -147,7 +156,7 @@ static struct bio *flush_delayed_bios(st
if (start_timer)
queue_timeout(dc, next_expires);
- return bio_list_get(&flush_bios);
+ flush_bios(bio_list_get(&flush_bio_list));
}
static void flush_expired_bios(struct work_struct *work)
@@ -158,7 +167,7 @@ static void flush_expired_bios(struct wo
if (delay_is_fast(dc))
flush_delayed_bios_fast(dc, false);
else
- flush_bios(flush_delayed_bios(dc, false));
+ flush_delayed_bios(dc, false);
}
static void delay_dtr(struct dm_target *ti)
@@ -177,8 +186,7 @@ static void delay_dtr(struct dm_target *
if (dc->worker)
kthread_stop(dc->worker);
- if (!delay_is_fast(dc))
- mutex_destroy(&dc->timer_lock);
+ mutex_destroy(&dc->timer_lock);
kfree(dc);
}
@@ -236,6 +244,7 @@ static int delay_ctr(struct dm_target *t
ti->private = dc;
INIT_LIST_HEAD(&dc->delayed_bios);
+ mutex_init(&dc->timer_lock);
dc->may_delay = true;
dc->argc = argc;
@@ -282,12 +291,12 @@ out:
"dm-delay-flush-worker");
if (IS_ERR(dc->worker)) {
ret = PTR_ERR(dc->worker);
+ dc->worker = NULL;
goto bad;
}
} else {
timer_setup(&dc->delay_timer, handle_delayed_timer, 0);
INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
- mutex_init(&dc->timer_lock);
dc->kdelayd_wq = alloc_workqueue("kdelayd", WQ_MEM_RECLAIM, 0);
if (!dc->kdelayd_wq) {
ret = -EINVAL;
@@ -345,11 +354,11 @@ static void delay_presuspend(struct dm_t
dc->may_delay = false;
mutex_unlock(&delayed_bios_lock);
- if (delay_is_fast(dc))
+ if (delay_is_fast(dc)) {
flush_delayed_bios_fast(dc, true);
- else {
+ } else {
del_timer_sync(&dc->delay_timer);
- flush_bios(flush_delayed_bios(dc, true));
+ flush_delayed_bios(dc, true);
}
}
