[pve-devel] [PATCH kernel] Backport two io-wq fixes relevant for io_uring
Fabian Ebner
f.ebner at proxmox.com
Tue Nov 23 12:59:48 CET 2021
There were quite a few reports in the community forum about Windows
VMs with SATA disks not working after upgrading to kernel 5.13.
Issue was reproducible during the installation of Win2019 (suggested
by Thomas), and it's already fixed in 5.15. Bisecting led to
io-wq: split bounded and unbounded work into separate lists
as the commit fixing the issue.
Indeed, the commit states
Fixes: ecc53c48c13d ("io-wq: check max_worker limits if a worker transitions bound state")
which is present as a backport in ubuntu-impish:
f9eb79f840052285408ae9082dc4419dc1397954
The first backport
io-wq: fix queue stalling race
also sounds nice to have and additionally served as a preparation for
the second one to apply more cleanly.
Signed-off-by: Fabian Ebner <f.ebner at proxmox.com>
---
.../0010-io-wq-fix-queue-stalling-race.patch | 72 +++
...ded-and-unbounded-work-into-separate.patch | 415 ++++++++++++++++++
2 files changed, 487 insertions(+)
create mode 100644 patches/kernel/0010-io-wq-fix-queue-stalling-race.patch
create mode 100644 patches/kernel/0011-io-wq-split-bounded-and-unbounded-work-into-separate.patch
diff --git a/patches/kernel/0010-io-wq-fix-queue-stalling-race.patch b/patches/kernel/0010-io-wq-fix-queue-stalling-race.patch
new file mode 100644
index 0000000..5ef160d
--- /dev/null
+++ b/patches/kernel/0010-io-wq-fix-queue-stalling-race.patch
@@ -0,0 +1,72 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jens Axboe <axboe at kernel.dk>
+Date: Tue, 31 Aug 2021 13:53:00 -0600
+Subject: [PATCH] io-wq: fix queue stalling race
+
+We need to set the stalled bit early, before we drop the lock for adding
+us to the stall hash queue. If not, then we can race with new work being
+queued between adding us to the stall hash and io_worker_handle_work()
+marking us stalled.
+
+Signed-off-by: Jens Axboe <axboe at kernel.dk>
+[backport]
+Signed-off-by: Fabian Ebner <f.ebner at proxmox.com>
+---
+ fs/io-wq.c | 15 +++++++--------
+ 1 file changed, 7 insertions(+), 8 deletions(-)
+
+diff --git a/fs/io-wq.c b/fs/io-wq.c
+index 6612d0aa497e..33678185f3bc 100644
+--- a/fs/io-wq.c
++++ b/fs/io-wq.c
+@@ -437,8 +437,7 @@ static bool io_worker_can_run_work(struct io_worker *worker,
+ }
+
+ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe,
+- struct io_worker *worker,
+- bool *stalled)
++ struct io_worker *worker)
+ __must_hold(wqe->lock)
+ {
+ struct io_wq_work_node *node, *prev;
+@@ -476,10 +475,14 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe,
+ }
+
+ if (stall_hash != -1U) {
++ /*
++ * Set this before dropping the lock to avoid racing with new
++ * work being added and clearing the stalled bit.
++ */
++ wqe->flags |= IO_WQE_FLAG_STALLED;
+ raw_spin_unlock(&wqe->lock);
+ io_wait_on_hash(wqe, stall_hash);
+ raw_spin_lock(&wqe->lock);
+- *stalled = true;
+ }
+
+ return NULL;
+@@ -519,7 +522,6 @@ static void io_worker_handle_work(struct io_worker *worker)
+
+ do {
+ struct io_wq_work *work;
+- bool stalled;
+ get_next:
+ /*
+ * If we got some work, mark us as busy. If we didn't, but
+@@ -528,12 +530,9 @@ static void io_worker_handle_work(struct io_worker *worker)
+ * can't make progress, any work completion or insertion will
+ * clear the stalled flag.
+ */
+- stalled = false;
+- work = io_get_next_work(wqe, worker, &stalled);
++ work = io_get_next_work(wqe, worker);
+ if (work)
+ __io_worker_busy(wqe, worker, work);
+- else if (stalled)
+- wqe->flags |= IO_WQE_FLAG_STALLED;
+
+ raw_spin_unlock_irq(&wqe->lock);
+ if (!work)
+--
+2.30.2
+
diff --git a/patches/kernel/0011-io-wq-split-bounded-and-unbounded-work-into-separate.patch b/patches/kernel/0011-io-wq-split-bounded-and-unbounded-work-into-separate.patch
new file mode 100644
index 0000000..47df331
--- /dev/null
+++ b/patches/kernel/0011-io-wq-split-bounded-and-unbounded-work-into-separate.patch
@@ -0,0 +1,415 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jens Axboe <axboe at kernel.dk>
+Date: Tue, 31 Aug 2021 13:57:32 -0600
+Subject: [PATCH] io-wq: split bounded and unbounded work into separate lists
+
+We've got a few issues that all boil down to the fact that we have one
+list of pending work items, yet two different types of workers to
+serve them. This causes some oddities around workers switching type and
+even hashed work vs regular work on the same bounded list.
+
+Just separate them out cleanly, similarly to how we already do
+accounting of what is running. That provides a clean separation and
+removes some corner cases that can cause stalls when handling IO
+that is punted to io-wq.
+
+Fixes: ecc53c48c13d ("io-wq: check max_worker limits if a worker transitions bound state")
+Signed-off-by: Jens Axboe <axboe at kernel.dk>
+[backport]
+Signed-off-by: Fabian Ebner <f.ebner at proxmox.com>
+---
+ fs/io-wq.c | 156 +++++++++++++++++++++++------------------------------
+ 1 file changed, 68 insertions(+), 88 deletions(-)
+
+diff --git a/fs/io-wq.c b/fs/io-wq.c
+index 33678185f3bc..2496d8781ea1 100644
+--- a/fs/io-wq.c
++++ b/fs/io-wq.c
+@@ -34,7 +34,7 @@ enum {
+ };
+
+ enum {
+- IO_WQE_FLAG_STALLED = 1, /* stalled on hash */
++ IO_ACCT_STALLED_BIT = 0, /* stalled on hash */
+ };
+
+ /*
+@@ -73,25 +73,24 @@ struct io_wqe_acct {
+ unsigned max_workers;
+ int index;
+ atomic_t nr_running;
++ struct io_wq_work_list work_list;
++ unsigned long flags;
+ };
+
+ enum {
+ IO_WQ_ACCT_BOUND,
+ IO_WQ_ACCT_UNBOUND,
++ IO_WQ_ACCT_NR,
+ };
+
+ /*
+ * Per-node worker thread pool
+ */
+ struct io_wqe {
+- struct {
+- raw_spinlock_t lock;
+- struct io_wq_work_list work_list;
+- unsigned flags;
+- } ____cacheline_aligned_in_smp;
++ raw_spinlock_t lock;
++ struct io_wqe_acct acct[2];
+
+ int node;
+- struct io_wqe_acct acct[2];
+
+ struct hlist_nulls_head free_list;
+ struct list_head all_list;
+@@ -196,11 +195,10 @@ static void io_worker_exit(struct io_worker *worker)
+ do_exit(0);
+ }
+
+-static inline bool io_wqe_run_queue(struct io_wqe *wqe)
+- __must_hold(wqe->lock)
++static inline bool io_acct_run_queue(struct io_wqe_acct *acct)
+ {
+- if (!wq_list_empty(&wqe->work_list) &&
+- !(wqe->flags & IO_WQE_FLAG_STALLED))
++ if (!wq_list_empty(&acct->work_list) &&
++ !test_bit(IO_ACCT_STALLED_BIT, &acct->flags))
+ return true;
+ return false;
+ }
+@@ -209,7 +207,8 @@ static inline bool io_wqe_run_queue(struct io_wqe *wqe)
+ * Check head of free list for an available worker. If one isn't available,
+ * caller must create one.
+ */
+-static bool io_wqe_activate_free_worker(struct io_wqe *wqe)
++static bool io_wqe_activate_free_worker(struct io_wqe *wqe,
++ struct io_wqe_acct *acct)
+ __must_hold(RCU)
+ {
+ struct hlist_nulls_node *n;
+@@ -223,6 +222,10 @@ static bool io_wqe_activate_free_worker(struct io_wqe *wqe)
+ hlist_nulls_for_each_entry_rcu(worker, n, &wqe->free_list, nulls_node) {
+ if (!io_worker_get(worker))
+ continue;
++ if (io_wqe_get_acct(worker) != acct) {
++ io_worker_release(worker);
++ continue;
++ }
+ if (wake_up_process(worker->task)) {
+ io_worker_release(worker);
+ return true;
+@@ -341,7 +344,7 @@ static void io_wqe_dec_running(struct io_worker *worker)
+ if (!(worker->flags & IO_WORKER_F_UP))
+ return;
+
+- if (atomic_dec_and_test(&acct->nr_running) && io_wqe_run_queue(wqe)) {
++ if (atomic_dec_and_test(&acct->nr_running) && io_acct_run_queue(acct)) {
+ atomic_inc(&acct->nr_running);
+ atomic_inc(&wqe->wq->worker_refs);
+ io_queue_worker_create(wqe, worker, acct);
+@@ -356,29 +359,10 @@ static void __io_worker_busy(struct io_wqe *wqe, struct io_worker *worker,
+ struct io_wq_work *work)
+ __must_hold(wqe->lock)
+ {
+- bool worker_bound, work_bound;
+-
+- BUILD_BUG_ON((IO_WQ_ACCT_UNBOUND ^ IO_WQ_ACCT_BOUND) != 1);
+-
+ if (worker->flags & IO_WORKER_F_FREE) {
+ worker->flags &= ~IO_WORKER_F_FREE;
+ hlist_nulls_del_init_rcu(&worker->nulls_node);
+ }
+-
+- /*
+- * If worker is moving from bound to unbound (or vice versa), then
+- * ensure we update the running accounting.
+- */
+- worker_bound = (worker->flags & IO_WORKER_F_BOUND) != 0;
+- work_bound = (work->flags & IO_WQ_WORK_UNBOUND) == 0;
+- if (worker_bound != work_bound) {
+- int index = work_bound ? IO_WQ_ACCT_UNBOUND : IO_WQ_ACCT_BOUND;
+- io_wqe_dec_running(worker);
+- worker->flags ^= IO_WORKER_F_BOUND;
+- wqe->acct[index].nr_workers--;
+- wqe->acct[index ^ 1].nr_workers++;
+- io_wqe_inc_running(worker);
+- }
+ }
+
+ /*
+@@ -417,44 +401,23 @@ static void io_wait_on_hash(struct io_wqe *wqe, unsigned int hash)
+ spin_unlock(&wq->hash->wait.lock);
+ }
+
+-/*
+- * We can always run the work if the worker is currently the same type as
+- * the work (eg both are bound, or both are unbound). If they are not the
+- * same, only allow it if incrementing the worker count would be allowed.
+- */
+-static bool io_worker_can_run_work(struct io_worker *worker,
+- struct io_wq_work *work)
+-{
+- struct io_wqe_acct *acct;
+-
+- if (!(worker->flags & IO_WORKER_F_BOUND) !=
+- !(work->flags & IO_WQ_WORK_UNBOUND))
+- return true;
+-
+- /* not the same type, check if we'd go over the limit */
+- acct = io_work_get_acct(worker->wqe, work);
+- return acct->nr_workers < acct->max_workers;
+-}
+-
+-static struct io_wq_work *io_get_next_work(struct io_wqe *wqe,
++static struct io_wq_work *io_get_next_work(struct io_wqe_acct *acct,
+ struct io_worker *worker)
+ __must_hold(wqe->lock)
+ {
+ struct io_wq_work_node *node, *prev;
+ struct io_wq_work *work, *tail;
+ unsigned int stall_hash = -1U;
++ struct io_wqe *wqe = worker->wqe;
+
+- wq_list_for_each(node, prev, &wqe->work_list) {
++ wq_list_for_each(node, prev, &acct->work_list) {
+ unsigned int hash;
+
+ work = container_of(node, struct io_wq_work, list);
+
+- if (!io_worker_can_run_work(worker, work))
+- break;
+-
+ /* not hashed, can run anytime */
+ if (!io_wq_is_hashed(work)) {
+- wq_list_del(&wqe->work_list, node, prev);
++ wq_list_del(&acct->work_list, node, prev);
+ return work;
+ }
+
+@@ -465,7 +428,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe,
+ /* hashed, can run if not already running */
+ if (!test_and_set_bit(hash, &wqe->wq->hash->map)) {
+ wqe->hash_tail[hash] = NULL;
+- wq_list_cut(&wqe->work_list, &tail->list, prev);
++ wq_list_cut(&acct->work_list, &tail->list, prev);
+ return work;
+ }
+ if (stall_hash == -1U)
+@@ -479,7 +442,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe,
+ * Set this before dropping the lock to avoid racing with new
+ * work being added and clearing the stalled bit.
+ */
+- wqe->flags |= IO_WQE_FLAG_STALLED;
++ set_bit(IO_ACCT_STALLED_BIT, &acct->flags);
+ raw_spin_unlock(&wqe->lock);
+ io_wait_on_hash(wqe, stall_hash);
+ raw_spin_lock(&wqe->lock);
+@@ -516,6 +479,7 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work);
+ static void io_worker_handle_work(struct io_worker *worker)
+ __releases(wqe->lock)
+ {
++ struct io_wqe_acct *acct = io_wqe_get_acct(worker);
+ struct io_wqe *wqe = worker->wqe;
+ struct io_wq *wq = wqe->wq;
+ bool do_kill = test_bit(IO_WQ_BIT_EXIT, &wq->state);
+@@ -530,7 +494,7 @@ static void io_worker_handle_work(struct io_worker *worker)
+ * can't make progress, any work completion or insertion will
+ * clear the stalled flag.
+ */
+- work = io_get_next_work(wqe, worker);
++ work = io_get_next_work(acct, worker);
+ if (work)
+ __io_worker_busy(wqe, worker, work);
+
+@@ -564,10 +528,10 @@ static void io_worker_handle_work(struct io_worker *worker)
+
+ if (hash != -1U && !next_hashed) {
+ clear_bit(hash, &wq->hash->map);
++ clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
+ if (wq_has_sleeper(&wq->hash->wait))
+ wake_up(&wq->hash->wait);
+ raw_spin_lock_irq(&wqe->lock);
+- wqe->flags &= ~IO_WQE_FLAG_STALLED;
+ /* skip unnecessary unlock-lock wqe->lock */
+ if (!work)
+ goto get_next;
+@@ -582,6 +546,7 @@ static void io_worker_handle_work(struct io_worker *worker)
+ static int io_wqe_worker(void *data)
+ {
+ struct io_worker *worker = data;
++ struct io_wqe_acct *acct = io_wqe_get_acct(worker);
+ struct io_wqe *wqe = worker->wqe;
+ struct io_wq *wq = wqe->wq;
+ char buf[TASK_COMM_LEN];
+@@ -597,7 +562,7 @@ static int io_wqe_worker(void *data)
+ set_current_state(TASK_INTERRUPTIBLE);
+ loop:
+ raw_spin_lock_irq(&wqe->lock);
+- if (io_wqe_run_queue(wqe)) {
++ if (io_acct_run_queue(acct)) {
+ io_worker_handle_work(worker);
+ goto loop;
+ }
+@@ -623,7 +588,7 @@ static int io_wqe_worker(void *data)
+
+ if (test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
+ raw_spin_lock_irq(&wqe->lock);
+- if (!wq_list_empty(&wqe->work_list))
++ if (!wq_list_empty(&acct->work_list))
+ io_worker_handle_work(worker);
+ else
+ raw_spin_unlock_irq(&wqe->lock);
+@@ -769,12 +734,13 @@ static void io_run_cancel(struct io_wq_work *work, struct io_wqe *wqe)
+
+ static void io_wqe_insert_work(struct io_wqe *wqe, struct io_wq_work *work)
+ {
++ struct io_wqe_acct *acct = io_work_get_acct(wqe, work);
+ unsigned int hash;
+ struct io_wq_work *tail;
+
+ if (!io_wq_is_hashed(work)) {
+ append:
+- wq_list_add_tail(&work->list, &wqe->work_list);
++ wq_list_add_tail(&work->list, &acct->work_list);
+ return;
+ }
+
+@@ -784,7 +750,7 @@ static void io_wqe_insert_work(struct io_wqe *wqe, struct io_wq_work *work)
+ if (!tail)
+ goto append;
+
+- wq_list_add_after(&work->list, &tail->list, &wqe->work_list);
++ wq_list_add_after(&work->list, &tail->list, &acct->work_list);
+ }
+
+ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
+@@ -806,10 +772,10 @@ static void io_wqe_enqueue(struct io_wqe *wqe, struct io_wq_work *work)
+
+ raw_spin_lock_irqsave(&wqe->lock, flags);
+ io_wqe_insert_work(wqe, work);
+- wqe->flags &= ~IO_WQE_FLAG_STALLED;
++ clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
+
+ rcu_read_lock();
+- do_create = !io_wqe_activate_free_worker(wqe);
++ do_create = !io_wqe_activate_free_worker(wqe, acct);
+ rcu_read_unlock();
+
+ raw_spin_unlock_irqrestore(&wqe->lock, flags);
+@@ -862,6 +828,7 @@ static inline void io_wqe_remove_pending(struct io_wqe *wqe,
+ struct io_wq_work *work,
+ struct io_wq_work_node *prev)
+ {
++ struct io_wqe_acct *acct = io_work_get_acct(wqe, work);
+ unsigned int hash = io_get_work_hash(work);
+ struct io_wq_work *prev_work = NULL;
+
+@@ -873,7 +840,7 @@ static inline void io_wqe_remove_pending(struct io_wqe *wqe,
+ else
+ wqe->hash_tail[hash] = NULL;
+ }
+- wq_list_del(&wqe->work_list, &work->list, prev);
++ wq_list_del(&acct->work_list, &work->list, prev);
+ }
+
+ static void io_wqe_cancel_pending_work(struct io_wqe *wqe,
+@@ -882,22 +849,27 @@ static void io_wqe_cancel_pending_work(struct io_wqe *wqe,
+ struct io_wq_work_node *node, *prev;
+ struct io_wq_work *work;
+ unsigned long flags;
++ int i;
+
+ retry:
+ raw_spin_lock_irqsave(&wqe->lock, flags);
+- wq_list_for_each(node, prev, &wqe->work_list) {
+- work = container_of(node, struct io_wq_work, list);
+- if (!match->fn(work, match->data))
+- continue;
+- io_wqe_remove_pending(wqe, work, prev);
+- raw_spin_unlock_irqrestore(&wqe->lock, flags);
+- io_run_cancel(work, wqe);
+- match->nr_pending++;
+- if (!match->cancel_all)
+- return;
++ for (i = 0; i < IO_WQ_ACCT_NR; i++) {
++ struct io_wqe_acct *acct = io_get_acct(wqe, i == 0);
+
+- /* not safe to continue after unlock */
+- goto retry;
++ wq_list_for_each(node, prev, &acct->work_list) {
++ work = container_of(node, struct io_wq_work, list);
++ if (!match->fn(work, match->data))
++ continue;
++ io_wqe_remove_pending(wqe, work, prev);
++ raw_spin_unlock_irqrestore(&wqe->lock, flags);
++ io_run_cancel(work, wqe);
++ match->nr_pending++;
++ if (!match->cancel_all)
++ return;
++
++ /* not safe to continue after unlock */
++ goto retry;
++ }
+ }
+ raw_spin_unlock_irqrestore(&wqe->lock, flags);
+ }
+@@ -958,18 +930,24 @@ static int io_wqe_hash_wake(struct wait_queue_entry *wait, unsigned mode,
+ int sync, void *key)
+ {
+ struct io_wqe *wqe = container_of(wait, struct io_wqe, wait);
++ int i;
+
+ list_del_init(&wait->entry);
+
+ rcu_read_lock();
+- io_wqe_activate_free_worker(wqe);
++ for (i = 0; i < IO_WQ_ACCT_NR; i++) {
++ struct io_wqe_acct *acct = &wqe->acct[i];
++
++ if (test_and_clear_bit(IO_ACCT_STALLED_BIT, &acct->flags))
++ io_wqe_activate_free_worker(wqe, acct);
++ }
+ rcu_read_unlock();
+ return 1;
+ }
+
+ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
+ {
+- int ret = -ENOMEM, node;
++ int ret, node, i;
+ struct io_wq *wq;
+
+ if (WARN_ON_ONCE(!data->free_work || !data->do_work))
+@@ -1006,18 +984,20 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
+ goto err;
+ wq->wqes[node] = wqe;
+ wqe->node = alloc_node;
+- wqe->acct[IO_WQ_ACCT_BOUND].index = IO_WQ_ACCT_BOUND;
+- wqe->acct[IO_WQ_ACCT_UNBOUND].index = IO_WQ_ACCT_UNBOUND;
+ wqe->acct[IO_WQ_ACCT_BOUND].max_workers = bounded;
+- atomic_set(&wqe->acct[IO_WQ_ACCT_BOUND].nr_running, 0);
+ wqe->acct[IO_WQ_ACCT_UNBOUND].max_workers =
+ task_rlimit(current, RLIMIT_NPROC);
+- atomic_set(&wqe->acct[IO_WQ_ACCT_UNBOUND].nr_running, 0);
+- wqe->wait.func = io_wqe_hash_wake;
+ INIT_LIST_HEAD(&wqe->wait.entry);
++ wqe->wait.func = io_wqe_hash_wake;
++ for (i = 0; i < IO_WQ_ACCT_NR; i++) {
++ struct io_wqe_acct *acct = &wqe->acct[i];
++
++ acct->index = i;
++ atomic_set(&acct->nr_running, 0);
++ INIT_WQ_LIST(&acct->work_list);
++ }
+ wqe->wq = wq;
+ raw_spin_lock_init(&wqe->lock);
+- INIT_WQ_LIST(&wqe->work_list);
+ INIT_HLIST_NULLS_HEAD(&wqe->free_list, 0);
+ INIT_LIST_HEAD(&wqe->all_list);
+ }
+--
+2.30.2
+
--
2.30.2
More information about the pve-devel
mailing list