The patch titled
pm: fix suspend_console/resume_console to use only one semaphore
has been added to the -mm tree. Its filename is
pm-fix-suspend_console-resume_console-to-use-only-one-semaphore.patch
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Subject: pm: fix suspend_console/resume_console to use only one semaphore
From: Arve Hjønnevåg <arve@xxxxxxxxxxx>
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 <arve@xxxxxxxxxxx>
Cc: Brian Swetland <swetland@xxxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
Cc: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/printk.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff -puN kernel/printk.c~pm-fix-suspend_console-resume_console-to-use-only-one-semaphore kernel/printk.c
--- a/kernel/printk.c~pm-fix-suspend_console-resume_console-to-use-only-one-semaphore
+++ a/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);
@@ -891,12 +890,14 @@ 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();
}
@@ -912,11 +913,9 @@ 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;
}
@@ -926,6 +925,10 @@ 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;
@@ -979,7 +982,7 @@ void release_console_sem(void)
unsigned wake_klogd = 0;
if (console_suspended) {
- up(&secondary_console_sem);
+ up(&console_sem);
return;
}
_
Patches currently in -mm which might be from arve@xxxxxxxxxxx are
origin.patch
pm-wait-for-console-in-resume.patch
pm-fix-suspend_console-resume_console-to-use-only-one-semaphore.patch
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