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rcu: Fix unrecovered RCU user mode in syscall_trace_leave()

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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>
This commit is contained in:
Frederic Weisbecker 2012-10-26 11:40:28 +02:00 committed by Paul E. McKenney
parent 6f0c0580b7
commit 2c5594df34
1 changed files with 7 additions and 0 deletions
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7
arch/x86/kernel/ptrace.c
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@ -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)))