path: root/Documentation/RCU/whatisRCU.txt
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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 /Documentation/RCU/whatisRCU.txt
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>
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