2009-01-31 03:28:13

by Arve Hjønnevåg

Subject: [PATCH 1/2] PM: Wait for console in resume.

Avoids later waking up to a blinking cursor if the device
woke up and returned to sleep before the console switch happened.

Signed-off-by: Brian Swetland <[email protected]>
Signed-off-by: Arve Hjønnevåg <[email protected]>
---
kernel/power/console.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/kernel/power/console.c b/kernel/power/console.c
index b8628be..a3961b2 100644
--- a/kernel/power/console.c
+++ b/kernel/power/console.c
@@ -78,6 +78,12 @@ void pm_restore_console(void)
}
set_console(orig_fgconsole);
release_console_sem();
+
+ if (vt_waitactive(orig_fgconsole)) {
+ pr_debug("Resume: Can't switch VCs.");
+ return;
+ }
+
kmsg_redirect = orig_kmsg;
}
#endif
--
1.6.1

2009-01-31 03:28:41

by Arve Hjønnevåg

Subject: [PATCH 2/2] PM: Fix suspend_console/resume_console to use only one semaphore.

This fixes a race if another thread acquired the console
while it was suspended and released it after it was resumed
the secondary console semaphre would be left locked, and the
primary semaphore would be released twice. This in turn caused
the console switch on suspend or resume to hang forever.

Note that suspend_console does not actually lock the console
for clients that use acquire_console_sem, it only locks it for
clients that use try_acquire_console_sem. If we change
suspend_console to fully lock the console, then the kernel
may deadlock on suspend.

Signed-off-by: Arve Hjønnevåg <[email protected]>
---
kernel/printk.c | 15 +++++++++------
1 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index 7015733..118ee77 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -73,7 +73,6 @@ EXPORT_SYMBOL(oops_in_progress);
* driver system.
*/
static DECLARE_MUTEX(console_sem);
-static DECLARE_MUTEX(secondary_console_sem);
struct console *console_drivers;
EXPORT_SYMBOL_GPL(console_drivers);

@@ -896,12 +895,14 @@ void suspend_console(void)
printk("Suspending console(s) (use no_console_suspend to debug)\n");
acquire_console_sem();
console_suspended = 1;
+ up(&console_sem);
}

void resume_console(void)
{
if (!console_suspend_enabled)
return;
+ down(&console_sem);
console_suspended = 0;
release_console_sem();
}
@@ -917,11 +918,9 @@ void resume_console(void)
void acquire_console_sem(void)
{
BUG_ON(in_interrupt());
- if (console_suspended) {
- down(&secondary_console_sem);
- return;
- }
down(&console_sem);
+ if (console_suspended)
+ return;
console_locked = 1;
console_may_schedule = 1;
}
@@ -931,6 +930,10 @@ int try_acquire_console_sem(void)
{
if (down_trylock(&console_sem))
return -1;
+ if (console_suspended) {
+ up(&console_sem);
+ return -1;
+ }
console_locked = 1;
console_may_schedule = 0;
return 0;
@@ -984,7 +987,7 @@ void release_console_sem(void)
unsigned wake_klogd = 0;

if (console_suspended) {
- up(&secondary_console_sem);
+ up(&console_sem);
return;
}

--
1.6.1