• Peter Zijlstra's avatar
    perf: Fix perf_lock_task_context() vs RCU · 058ebd0e
    Peter Zijlstra authored
    Jiri managed to trigger this warning:
    
     [] ======================================================
     [] [ INFO: possible circular locking dependency detected ]
     [] 3.10.0+ #228 Tainted: G        W
     [] -------------------------------------------------------
     [] p/6613 is trying to acquire lock:
     []  (rcu_node_0){..-...}, at: [<ffffffff810ca797>] rcu_read_unlock_special+0xa7/0x250
     []
     [] but task is already holding lock:
     []  (&ctx->lock){-.-...}, at: [<ffffffff810f2879>] perf_lock_task_context+0xd9/0x2c0
     []
     [] which lock already depends on the new lock.
     []
     [] the existing dependency chain (in reverse order) is:
     []
     [] -> #4 (&ctx->lock){-.-...}:
     [] -> #3 (&rq->lock){-.-.-.}:
     [] -> #2 (&p->pi_lock){-.-.-.}:
     [] -> #1 (&rnp->nocb_gp_wq[1]){......}:
     [] -> #0 (rcu_node_0){..-...}:
    
    Paul was quick to explain that due to preemptible RCU we cannot call
    rcu_read_unlock() while holding scheduler (or nested) locks when part
    of the read side critical section was preemptible.
    
    Therefore solve it by making the entire RCU read side non-preemptible.
    
    Also pull out the retry from under the non-preempt to play nice with RT.
    Reported-by: default avatarJiri Olsa <jolsa@redhat.com>
    Helped-out-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: <stable@kernel.org>
    Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    058ebd0e
core.c 183 KB