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authorFrederic Weisbecker <fweisbec@gmail.com>2012-10-26 11:40:28 +0200
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-10-27 15:42:00 -0700
commit2c5594df344cd1ff0cc9bf007dea3235582b3acf (patch)
treec41a0f3ca974f722d517ee87b956c716b2c69a11
parent6f0c0580b70c89094b3422ba81118c7b959c7556 (diff)
rcu: Fix unrecovered RCU user mode in syscall_trace_leave()
On x86-64 syscall exit, 3 non exclusive events may happen looping in the following order: 1) Check if we need resched for user preemption, if so call schedule_user() 2) Check if we have pending signals, if so call do_notify_resume() 3) Check if we do syscall tracing, if so call syscall_trace_leave() However syscall_trace_leave() has been written assuming it directly follows the syscall and forget about the above possible 1st and 2nd steps. Now schedule_user() and do_notify_resume() exit in RCU user mode because they have most chances to resume userspace immediately and this avoids an rcu_user_enter() call in the syscall fast path. So by the time we call syscall_trace_leave(), we may well be in RCU user mode. To fix this up, simply call rcu_user_exit() in the beginning of this function. This fixes some reported RCU uses in extended quiescent state. Reported-by: Dave Jones <davej@redhat.com> Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Tested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
-rw-r--r--arch/x86/kernel/ptrace.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index b00b33a18390..eff5b8c68652 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1511,6 +1511,13 @@ void syscall_trace_leave(struct pt_regs *regs)
{
bool step;
+ /*
+ * We may come here right after calling schedule_user()
+ * or do_notify_resume(), in which case we can be in RCU
+ * user mode.
+ */
+ rcu_user_exit();
+
audit_syscall_exit(regs);
if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))