[PATCH 1/4] speakup: Stop catch_up when the synth is not alive

[Hongyu Xie]

When the synth output cannot make progress, the catch-up loop in
_spk_do_catch_up() (and in its local copies in the serial synth
drivers) can spin forever: nothing tells it that the synth is dead.
This happens

- when the tty write keeps returning 0 (no room) because nothing
  consumes the data, e.g. a serial port with no device attached that
  keeps flow control asserted, or
- when an I/O error deactivates the synth: synth_out() then keeps
  returning 0 and the loop never notices that synth->alive became 0.

While speakup_thread() holds spk_mutex across the whole loop, any
synth_add(), synth_remove() or synth_init() then blocks forever,
which gets reported as a hung task on module unload:

 INFO: task modprobe:2999919 blocked for more than 120 seconds.
  mutex_lock+0x54/0x68
  synth_remove+0x28/0xb8 [speakup]
 INFO: task modprobe:2999919 is blocked on a mutex likely owned
  by task speakup:
  schedule_timeout+...
  _spk_do_catch_up+...
  speakup_thread+...

Check synth->alive in the loops as well, so that catch_up() stops as
soon as the synth is dead.  synth_release() writes it under
speakup_info.spinlock, while the I/O error paths write it without the
lock; that is fine, since the loops only need to eventually observe
the change.

On its own this fixes the I/O error case, where the synth is already
deactivated when the loop retries.  In the no-room case nothing
clears synth->alive, and speakup_thread() still holds spk_mutex
across the loop, so nothing can get in to deactivate the synth; the
follow-up patch completes the fix by clearing synth->alive from
synth_release() and by dropping spk_mutex from the catch_up() call.

Fixes: 2067fd92d75b6 ("staging/speakup: Move out of staging")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
Signed-off-by: Hongyu Xie <xiehongyu1@xxxxxxxxxx>
---
 drivers/accessibility/speakup/speakup_acntpc.c | 4 ++++
 drivers/accessibility/speakup/speakup_apollo.c | 4 ++++
 drivers/accessibility/speakup/speakup_decext.c | 4 ++++
 drivers/accessibility/speakup/speakup_decpc.c  | 4 ++++
 drivers/accessibility/speakup/speakup_dectlk.c | 4 ++++
 drivers/accessibility/speakup/speakup_dtlk.c   | 4 ++++
 drivers/accessibility/speakup/speakup_keypc.c  | 4 ++++
 drivers/accessibility/speakup/synth.c          | 4 ++++
 8 files changed, 32 insertions(+)

diff --git a/drivers/accessibility/speakup/speakup_acntpc.c b/drivers/accessibility/speakup/speakup_acntpc.c
index a27e6bbf05da3..fe19ba3f00053 100644
--- a/drivers/accessibility/speakup/speakup_acntpc.c
+++ b/drivers/accessibility/speakup/speakup_acntpc.c
@@ -192,6 +192,10 @@ static void do_catch_up(struct spk_synth *synth)
 	jiff_max = jiffies + jiffy_delta_val;
 	while (!kthread_should_stop()) {
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
diff --git a/drivers/accessibility/speakup/speakup_apollo.c b/drivers/accessibility/speakup/speakup_apollo.c
index d2fbb3f572219..b62696e050fc0 100644
--- a/drivers/accessibility/speakup/speakup_apollo.c
+++ b/drivers/accessibility/speakup/speakup_apollo.c
@@ -157,6 +157,10 @@ static void do_catch_up(struct spk_synth *synth)
 
 	while (!kthread_should_stop()) {
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		jiffy_delta_val = jiffy_delta->u.n.value;
 		full_time_val = full_time->u.n.value;
 		delay_time_val = delay_time->u.n.value;
diff --git a/drivers/accessibility/speakup/speakup_decext.c b/drivers/accessibility/speakup/speakup_decext.c
index 271bcf279bf9b..e6be5a99670bd 100644
--- a/drivers/accessibility/speakup/speakup_decext.c
+++ b/drivers/accessibility/speakup/speakup_decext.c
@@ -171,6 +171,10 @@ static void do_catch_up(struct spk_synth *synth)
 
 	while (!kthread_should_stop()) {
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
diff --git a/drivers/accessibility/speakup/speakup_decpc.c b/drivers/accessibility/speakup/speakup_decpc.c
index 1bf36d1e54773..cfafd94759639 100644
--- a/drivers/accessibility/speakup/speakup_decpc.c
+++ b/drivers/accessibility/speakup/speakup_decpc.c
@@ -391,6 +391,10 @@ static void do_catch_up(struct spk_synth *synth)
 
 	while (!kthread_should_stop()) {
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
diff --git a/drivers/accessibility/speakup/speakup_dectlk.c b/drivers/accessibility/speakup/speakup_dectlk.c
index 56334405d865c..d9247c53d3275 100644
--- a/drivers/accessibility/speakup/speakup_dectlk.c
+++ b/drivers/accessibility/speakup/speakup_dectlk.c
@@ -246,6 +246,10 @@ static void do_catch_up(struct spk_synth *synth)
 		spin_unlock_irqrestore(&flush_lock, flags);
 
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
diff --git a/drivers/accessibility/speakup/speakup_dtlk.c b/drivers/accessibility/speakup/speakup_dtlk.c
index fa826568937bf..73cd39e781b86 100644
--- a/drivers/accessibility/speakup/speakup_dtlk.c
+++ b/drivers/accessibility/speakup/speakup_dtlk.c
@@ -206,6 +206,10 @@ static void do_catch_up(struct spk_synth *synth)
 	jiff_max = jiffies + jiffy_delta_val;
 	while (!kthread_should_stop()) {
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
diff --git a/drivers/accessibility/speakup/speakup_keypc.c b/drivers/accessibility/speakup/speakup_keypc.c
index 9356f63795603..e229009107f75 100644
--- a/drivers/accessibility/speakup/speakup_keypc.c
+++ b/drivers/accessibility/speakup/speakup_keypc.c
@@ -193,6 +193,10 @@ static void do_catch_up(struct spk_synth *synth)
 	jiff_max = jiffies + jiffy_delta_val;
 	while (!kthread_should_stop()) {
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
diff --git a/drivers/accessibility/speakup/synth.c b/drivers/accessibility/speakup/synth.c
index 11cba1fd8715d..6a49ff475c16a 100644
--- a/drivers/accessibility/speakup/synth.c
+++ b/drivers/accessibility/speakup/synth.c
@@ -75,6 +75,10 @@ static void _spk_do_catch_up(struct spk_synth *synth, int unicode)
 	jiff_max = jiffies + jiffy_delta_val;
 	while (!kthread_should_stop()) {
 		spin_lock_irqsave(&speakup_info.spinlock, flags);
+		if (!synth->alive) {
+			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
+			break;
+		}
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			spin_unlock_irqrestore(&speakup_info.spinlock, flags);
-- 
2.25.1