This fixes a race if another thread acquired the consolewhile it was suspended and released it after it was resumedthe secondary console semaphre would be left locked, and theprimary semaphore would be released twice. This in turn causedthe console switch on suspend or resume to hang forever.
Note that suspend_console does not actually lock the consolefor clients that use acquire_console_sem, it only locks it forclients that use try_acquire_console_sem. If we changesuspend_console to fully lock the console, then the kernelmay deadlock on suspend.
Signed-off-by: Arve Hjønnevåg <arve@xxxxxxxxxxx>--- kernel/printk.c | 15 +++++++++------ 1 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/kernel/printk.c b/kernel/printk.cindex 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
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