From: Michal Januszewski <[EMAIL PROTECTED]>
On a multiprocessor machine the VT_WAITACTIVE ioctl call may return 0
if fg_console has already been updated in redraw_screen() but the
console switch itself hasn't been completed. Fix this by checking
fg_console in vt_waitactive() with the console sem held.
Signed-off-by: Michal Januszewski <[EMAIL PROTECTED]>
---
This is the 2nd version of this patch. It incorporates Andrew's
suggestions, ie. calls set_current_state() after down() and adds
a comment explaining why acquiring the console sem is necessary.
drivers/char/vt_ioctl.c | 14 ++++++++++++--
1 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index 1fa2da8..0508293 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -1039,10 +1039,20 @@ int vt_waitactive(int vt)
add_wait_queue(&vt_activate_queue, &wait);
for (;;) {
- set_current_state(TASK_INTERRUPTIBLE);
retval = 0;
- if (vt == fg_console)
+
+ /* Synchronize with redraw_screen(). By acquiring the console
+ * semaphore we make sure that the console switch is completed
+ * before we return. If we didn't wait for the semaphore, we
+ * could return at a point where fg_console has already been
+ * updated, but the console switch hasn't been completed. */
+ acquire_console_sem();
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (vt == fg_console) {
+ release_console_sem();
break;
+ }
+ release_console_sem();
retval = -EINTR;
if (signal_pending(current))
break;
-
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