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Commit 403f307576396f3362fbb65af190885b6036c72c

Authored by Arve Hjønnevåg
Committed by Linus Torvalds
1 parent b090f9fa53
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

PM: Fix suspend_console and resume_console to use only one semaphore 

This fixes a race where a thread acquires the console while the
console is suspended, and the console is resumed before this
thread releases it. In this case, the secondary console
semaphore would be left locked, and the primary semaphore would
be released twice. This in turn would cause 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. One client of try_acquire_console_sem
is acquire_console_semaphore_for_printk, which uses it to
prevent printk from using the console while it is suspended.

Signed-off-by: Arve Hjønnevåg <arve@android.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Len Brown <lenb@kernel.org>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 9 additions and 6 deletions Side-by-side Diff

... ... @@ -73,7 +73,6 @@
73 73 * driver system.
74 74 */
75 75 static DECLARE_MUTEX(console_sem);
76   -static DECLARE_MUTEX(secondary_console_sem);
77 76 struct console *console_drivers;
78 77 EXPORT_SYMBOL_GPL(console_drivers);
79 78  
80 79  
... ... @@ -891,12 +890,14 @@
891 890 printk("Suspending console(s) (use no_console_suspend to debug)\n");
892 891 acquire_console_sem();
893 892 console_suspended = 1;
  893 + up(&console_sem);
894 894 }
895 895  
896 896 void resume_console(void)
897 897 {
898 898 if (!console_suspend_enabled)
899 899 return;
  900 + down(&console_sem);
900 901 console_suspended = 0;
901 902 release_console_sem();
902 903 }
903 904  
... ... @@ -912,11 +913,9 @@
912 913 void acquire_console_sem(void)
913 914 {
914 915 BUG_ON(in_interrupt());
915   - if (console_suspended) {
916   - down(&secondary_console_sem);
917   - return;
918   - }
919 916 down(&console_sem);
  917 + if (console_suspended)
  918 + return;
920 919 console_locked = 1;
921 920 console_may_schedule = 1;
922 921 }
... ... @@ -926,6 +925,10 @@
926 925 {
927 926 if (down_trylock(&console_sem))
928 927 return -1;
  928 + if (console_suspended) {
  929 + up(&console_sem);
  930 + return -1;
  931 + }
929 932 console_locked = 1;
930 933 console_may_schedule = 0;
931 934 return 0;
... ... @@ -979,7 +982,7 @@
979 982 unsigned wake_klogd = 0;
980 983  
981 984 if (console_suspended) {
982   - up(&secondary_console_sem);
  985 + up(&console_sem);
983 986 return;
984 987 }
985 988