From a9bf5c8a271b9a954709b7ada1bd258f5cadf7ff Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Tue, 1 May 2018 00:55:53 +1000
Subject: tty: hvc: use mutex instead of spinlock for hvc_structs lock
This allows hvc operations to sleep under the lock.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
drivers/tty/hvc/hvc_console.c | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 7709fcc707f4..fddb63322c67 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -73,7 +73,7 @@ static LIST_HEAD(hvc_structs);
* Protect the list of hvc_struct instances from inserts and removals during
* list traversal.
*/
-static DEFINE_SPINLOCK(hvc_structs_lock);
+static DEFINE_MUTEX(hvc_structs_mutex);
/*
* This value is used to assign a tty->index value to a hvc_struct based
@@ -83,7 +83,7 @@ static DEFINE_SPINLOCK(hvc_structs_lock);
static int last_hvc = -1;
/*
- * Do not call this function with either the hvc_structs_lock or the hvc_struct
+ * Do not call this function with either the hvc_structs_mutex or the hvc_struct
* lock held. If successful, this function increments the kref reference
* count against the target hvc_struct so it should be released when finished.
*/
@@ -92,25 +92,24 @@ static struct hvc_struct *hvc_get_by_index(int index)
struct hvc_struct *hp;
unsigned long flags;
- spin_lock(&hvc_structs_lock);
+ mutex_lock(&hvc_structs_mutex);
list_for_each_entry(hp, &hvc_structs, next) {
spin_lock_irqsave(&hp->lock, flags);
if (hp->index == index) {
tty_port_get(&hp->port);
spin_unlock_irqrestore(&hp->lock, flags);
- spin_unlock(&hvc_structs_lock);
+ mutex_unlock(&hvc_structs_mutex);
return hp;
}
spin_unlock_irqrestore(&hp->lock, flags);
}
hp = NULL;
+ mutex_unlock(&hvc_structs_mutex);
- spin_unlock(&hvc_structs_lock);
return hp;
}
-
/*
* Initial console vtermnos for console API usage prior to full console
* initialization. Any vty adapter outside this range will not have usable
@@ -224,13 +223,13 @@ static void hvc_port_destruct(struct tty_port *port)
struct hvc_struct *hp = container_of(port, struct hvc_struct, port);
unsigned long flags;
- spin_lock(&hvc_structs_lock);
+ mutex_lock(&hvc_structs_mutex);
spin_lock_irqsave(&hp->lock, flags);
list_del(&(hp->next));
spin_unlock_irqrestore(&hp->lock, flags);
- spin_unlock(&hvc_structs_lock);
+ mutex_unlock(&hvc_structs_mutex);
kfree(hp);
}
@@ -733,11 +732,11 @@ static int khvcd(void *unused)
try_to_freeze();
wmb();
if (!cpus_are_in_xmon()) {
- spin_lock(&hvc_structs_lock);
+ mutex_lock(&hvc_structs_mutex);
list_for_each_entry(hp, &hvc_structs, next) {
poll_mask |= hvc_poll(hp);
}
- spin_unlock(&hvc_structs_lock);
+ mutex_unlock(&hvc_structs_mutex);
} else
poll_mask |= HVC_POLL_READ;
if (hvc_kicked)
@@ -871,7 +870,7 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data,
INIT_WORK(&hp->tty_resize, hvc_set_winsz);
spin_lock_init(&hp->lock);
- spin_lock(&hvc_structs_lock);
+ mutex_lock(&hvc_structs_mutex);
/*
* find index to use:
@@ -891,7 +890,7 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data,
vtermnos[i] = vtermno;
list_add_tail(&(hp->next), &hvc_structs);
- spin_unlock(&hvc_structs_lock);
+ mutex_unlock(&hvc_structs_mutex);
/* check if we need to re-register the kernel console */
hvc_check_console(i);
--
cgit v1.2.3
From ec97eaad1383ab2500fcf9a07ade6044fbcc67f5 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Tue, 1 May 2018 00:55:54 +1000
Subject: tty: hvc: hvc_poll() break hv read loop
Avoid looping with the spinlock held while there is read data
being returned from the hv driver. Instead note if the entire
size returned by tty_buffer_request_room was read, and request
another read poll.
This limits the critical section lengths, and provides more
even service to other consoles in case there is a pathological
condition.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
drivers/tty/hvc/hvc_console.c | 88 ++++++++++++++++++++++---------------------
1 file changed, 45 insertions(+), 43 deletions(-)
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index fddb63322c67..745ac220fce8 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -592,7 +592,7 @@ static u32 timeout = MIN_TIMEOUT;
int hvc_poll(struct hvc_struct *hp)
{
struct tty_struct *tty;
- int i, n, poll_mask = 0;
+ int i, n, count, poll_mask = 0;
char buf[N_INBUF] __ALIGNED__;
unsigned long flags;
int read_total = 0;
@@ -618,7 +618,7 @@ int hvc_poll(struct hvc_struct *hp)
/* Now check if we can get data (are we throttled ?) */
if (tty_throttled(tty))
- goto throttled;
+ goto out;
/* If we aren't notifier driven and aren't throttled, we always
* request a reschedule
@@ -627,56 +627,58 @@ int hvc_poll(struct hvc_struct *hp)
poll_mask |= HVC_POLL_READ;
/* Read data if any */
- for (;;) {
- int count = tty_buffer_request_room(&hp->port, N_INBUF);
- /* If flip is full, just reschedule a later read */
- if (count == 0) {
+ count = tty_buffer_request_room(&hp->port, N_INBUF);
+
+ /* If flip is full, just reschedule a later read */
+ if (count == 0) {
+ poll_mask |= HVC_POLL_READ;
+ goto out;
+ }
+
+ n = hp->ops->get_chars(hp->vtermno, buf, count);
+ if (n <= 0) {
+ /* Hangup the tty when disconnected from host */
+ if (n == -EPIPE) {
+ spin_unlock_irqrestore(&hp->lock, flags);
+ tty_hangup(tty);
+ spin_lock_irqsave(&hp->lock, flags);
+ } else if ( n == -EAGAIN ) {
+ /*
+ * Some back-ends can only ensure a certain min
+ * num of bytes read, which may be > 'count'.
+ * Let the tty clear the flip buff to make room.
+ */
poll_mask |= HVC_POLL_READ;
- break;
}
+ goto out;
+ }
- n = hp->ops->get_chars(hp->vtermno, buf, count);
- if (n <= 0) {
- /* Hangup the tty when disconnected from host */
- if (n == -EPIPE) {
- spin_unlock_irqrestore(&hp->lock, flags);
- tty_hangup(tty);
- spin_lock_irqsave(&hp->lock, flags);
- } else if ( n == -EAGAIN ) {
- /*
- * Some back-ends can only ensure a certain min
- * num of bytes read, which may be > 'count'.
- * Let the tty clear the flip buff to make room.
- */
- poll_mask |= HVC_POLL_READ;
- }
- break;
- }
- for (i = 0; i < n; ++i) {
+ for (i = 0; i < n; ++i) {
#ifdef CONFIG_MAGIC_SYSRQ
- if (hp->index == hvc_console.index) {
- /* Handle the SysRq Hack */
- /* XXX should support a sequence */
- if (buf[i] == '\x0f') { /* ^O */
- /* if ^O is pressed again, reset
- * sysrq_pressed and flip ^O char */
- sysrq_pressed = !sysrq_pressed;
- if (sysrq_pressed)
- continue;
- } else if (sysrq_pressed) {
- handle_sysrq(buf[i]);
- sysrq_pressed = 0;
+ if (hp->index == hvc_console.index) {
+ /* Handle the SysRq Hack */
+ /* XXX should support a sequence */
+ if (buf[i] == '\x0f') { /* ^O */
+ /* if ^O is pressed again, reset
+ * sysrq_pressed and flip ^O char */
+ sysrq_pressed = !sysrq_pressed;
+ if (sysrq_pressed)
continue;
- }
+ } else if (sysrq_pressed) {
+ handle_sysrq(buf[i]);
+ sysrq_pressed = 0;
+ continue;
}
-#endif /* CONFIG_MAGIC_SYSRQ */
- tty_insert_flip_char(&hp->port, buf[i], 0);
}
-
- read_total += n;
+#endif /* CONFIG_MAGIC_SYSRQ */
+ tty_insert_flip_char(&hp->port, buf[i], 0);
}
- throttled:
+ if (n == count)
+ poll_mask |= HVC_POLL_READ;
+ read_total = n;
+
+ out:
/* Wakeup write queue if necessary */
if (hp->do_wakeup) {
hp->do_wakeup = 0;
--
cgit v1.2.3
From cfb5946b55f1dfd19e042feae1fbff6041e25a98 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Tue, 1 May 2018 00:55:55 +1000
Subject: tty: hvc: hvc_poll() may sleep
Introduce points where hvc_poll drops the lock, enables interrupts,
and reschedules.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
drivers/tty/hvc/hvc_console.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 745ac220fce8..2abfc0b15fbb 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -589,7 +589,7 @@ static u32 timeout = MIN_TIMEOUT;
#define HVC_POLL_READ 0x00000001
#define HVC_POLL_WRITE 0x00000002
-int hvc_poll(struct hvc_struct *hp)
+static int __hvc_poll(struct hvc_struct *hp, bool may_sleep)
{
struct tty_struct *tty;
int i, n, count, poll_mask = 0;
@@ -611,6 +611,12 @@ int hvc_poll(struct hvc_struct *hp)
timeout = (written_total) ? 0 : MIN_TIMEOUT;
}
+ if (may_sleep) {
+ spin_unlock_irqrestore(&hp->lock, flags);
+ cond_resched();
+ spin_lock_irqsave(&hp->lock, flags);
+ }
+
/* No tty attached, just skip */
tty = tty_port_tty_get(&hp->port);
if (tty == NULL)
@@ -698,6 +704,11 @@ int hvc_poll(struct hvc_struct *hp)
return poll_mask;
}
+
+int hvc_poll(struct hvc_struct *hp)
+{
+ return __hvc_poll(hp, false);
+}
EXPORT_SYMBOL_GPL(hvc_poll);
/**
@@ -736,7 +747,8 @@ static int khvcd(void *unused)
if (!cpus_are_in_xmon()) {
mutex_lock(&hvc_structs_mutex);
list_for_each_entry(hp, &hvc_structs, next) {
- poll_mask |= hvc_poll(hp);
+ poll_mask |= __hvc_poll(hp, true);
+ cond_resched();
}
mutex_unlock(&hvc_structs_mutex);
} else
--
cgit v1.2.3
From 550ddadcc7580ec2a6c22d4ed04291bc6e2428fb Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Tue, 1 May 2018 00:55:56 +1000
Subject: tty: hvc: hvc_write() may sleep
Rework the hvc_write loop to drop and re-take the spinlock on each
iteration, add a cond_resched. Don't bother with an initial hvc_push
initially, which makes the logic simpler -- just do a hvc_push on
each time around the loop.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
drivers/tty/hvc/hvc_console.c | 36 +++++++++++++++++++++---------------
1 file changed, 21 insertions(+), 15 deletions(-)
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 2abfc0b15fbb..6131d5084c42 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -493,23 +493,29 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
if (hp->port.count <= 0)
return -EIO;
- spin_lock_irqsave(&hp->lock, flags);
+ while (count > 0) {
+ spin_lock_irqsave(&hp->lock, flags);
- /* Push pending writes */
- if (hp->n_outbuf > 0)
- hvc_push(hp);
-
- while (count > 0 && (rsize = hp->outbuf_size - hp->n_outbuf) > 0) {
- if (rsize > count)
- rsize = count;
- memcpy(hp->outbuf + hp->n_outbuf, buf, rsize);
- count -= rsize;
- buf += rsize;
- hp->n_outbuf += rsize;
- written += rsize;
- hvc_push(hp);
+ rsize = hp->outbuf_size - hp->n_outbuf;
+
+ if (rsize) {
+ if (rsize > count)
+ rsize = count;
+ memcpy(hp->outbuf + hp->n_outbuf, buf, rsize);
+ count -= rsize;
+ buf += rsize;
+ hp->n_outbuf += rsize;
+ written += rsize;
+ }
+
+ if (hp->n_outbuf > 0)
+ hvc_push(hp);
+
+ spin_unlock_irqrestore(&hp->lock, flags);
+
+ if (count)
+ cond_resched();
}
- spin_unlock_irqrestore(&hp->lock, flags);
/*
* Racy, but harmless, kick thread if there is still pending data.
--
cgit v1.2.3
From 9f65b81f36e31563c5a5e4df3b3b8bc7550b6030 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Tue, 1 May 2018 00:55:57 +1000
Subject: tty: hvc: introduce the hv_ops.flush operation for hvc drivers
Use .flush to wait for drivers to flush their console outside of
the spinlock, to reduce lock/irq latencies.
Flush the hvc console driver after each write, which can help
messages make it out to the console after a crash.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
drivers/tty/hvc/hvc_console.c | 35 +++++++++++++++++++++++++++++++++--
drivers/tty/hvc/hvc_console.h | 1 +
2 files changed, 34 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 6131d5084c42..5414c4a87bea 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -110,6 +110,29 @@ static struct hvc_struct *hvc_get_by_index(int index)
return hp;
}
+static int __hvc_flush(const struct hv_ops *ops, uint32_t vtermno, bool wait)
+{
+ if (wait)
+ might_sleep();
+
+ if (ops->flush)
+ return ops->flush(vtermno, wait);
+ return 0;
+}
+
+static int hvc_console_flush(const struct hv_ops *ops, uint32_t vtermno)
+{
+ return __hvc_flush(ops, vtermno, false);
+}
+
+/*
+ * Wait for the console to flush before writing more to it. This sleeps.
+ */
+static int hvc_flush(struct hvc_struct *hp)
+{
+ return __hvc_flush(hp->ops, hp->vtermno, true);
+}
+
/*
* Initial console vtermnos for console API usage prior to full console
* initialization. Any vty adapter outside this range will not have usable
@@ -155,8 +178,12 @@ static void hvc_console_print(struct console *co, const char *b,
if (r <= 0) {
/* throw away characters on error
* but spin in case of -EAGAIN */
- if (r != -EAGAIN)
+ if (r != -EAGAIN) {
i = 0;
+ } else {
+ hvc_console_flush(cons_ops[index],
+ vtermnos[index]);
+ }
} else if (r > 0) {
i -= r;
if (i > 0)
@@ -164,6 +191,7 @@ static void hvc_console_print(struct console *co, const char *b,
}
}
}
+ hvc_console_flush(cons_ops[index], vtermnos[index]);
}
static struct tty_driver *hvc_console_device(struct console *c, int *index)
@@ -513,8 +541,11 @@ static int hvc_write(struct tty_struct *tty, const unsigned char *buf, int count
spin_unlock_irqrestore(&hp->lock, flags);
- if (count)
+ if (count) {
+ if (hp->n_outbuf > 0)
+ hvc_flush(hp);
cond_resched();
+ }
}
/*
diff --git a/drivers/tty/hvc/hvc_console.h b/drivers/tty/hvc/hvc_console.h
index ea63090e013f..e9319954c832 100644
--- a/drivers/tty/hvc/hvc_console.h
+++ b/drivers/tty/hvc/hvc_console.h
@@ -54,6 +54,7 @@ struct hvc_struct {
struct hv_ops {
int (*get_chars)(uint32_t vtermno, char *buf, int count);
int (*put_chars)(uint32_t vtermno, const char *buf, int count);
+ int (*flush)(uint32_t vtermno, bool wait);
/* Callbacks for notification. Called in open, close and hangup */
int (*notifier_add)(struct hvc_struct *hp, int irq);
--
cgit v1.2.3