[PATCH] pacct: add pacct_struct to fix some pacct bugs.

The pacct facility need an i/o operation when an accounting record is
generated.  There is a possibility to wake OOM killer up.  If OOM killer is
activated, it kills some processes to make them release process memory
regions.

But acct_process() is called in the killed processes context before calling
exit_mm(), so those processes cannot release own memory.  In the results, any
processes stop in this point and it finally cause a system stall.

include/linux/sched.h

@@ -358,6 +358,10 @@ struct sighand_struct {
 	spinlock_t		siglock;
 };
 
+struct pacct_struct {
+	unsigned long		ac_mem;
+};
+
 /*
  * NOTE! "signal_struct" does not have it's own
  * locking, because a shared signal_struct always
@@ -449,6 +453,9 @@ struct signal_struct {
 	struct key *session_keyring;	/* keyring inherited over fork */
 	struct key *process_keyring;	/* keyring private to this process */
 #endif
+#ifdef CONFIG_BSD_PROCESS_ACCT
+	struct pacct_struct pacct;	/* per-process accounting information */
+#endif
 };
 
 /* Context switch must be unlocked if interrupts are to be enabled */