• Paul E. McKenney's avatar
    arm: Use _rcuidle for smp_cross_call() tracepoints · 7c64cc05
    Paul E. McKenney authored
    Further testing with false negatives suppressed by commit 293e2421
    ("rcu: Remove superfluous versions of rcu_read_lock_sched_held()")
    identified another unprotected use of RCU from the idle loop.  Because RCU
    actively ignores idle-loop code (for energy-efficiency reasons, among
    other things), using RCU from the idle loop can result in too-short
    grace periods, in turn resulting in arbitrary misbehavior.
    
    The resulting lockdep-RCU splat is as follows:
    
    ------------------------------------------------------------------------
    
    ===============================
    [ INFO: suspicious RCU usage. ]
    4.6.0-rc5-next-20160426+ #1112 Not tainted
    -------------------------------
    include/trace/events/ipi.h:35 suspicious rcu_dereference_check() usage!
    
    other info that might help us debug this:
    
    RCU used illegally from idle CPU!
    rcu_scheduler_active = 1, debug_locks = 0
    RCU used illegally from extended quiescent state!
    no locks held by swapper/0/0.
    
    stack backtrace:
    CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.6.0-rc5-next-20160426+ #1112
    Hardware name: Generic OMAP4 (Flattened Device Tree)
    [<c0110308>] (unwind_backtrace) from [<c010c3a8>] (show_stack+0x10/0x14)
    [<c010c3a8>] (show_stack) from [<c047fec8>] (dump_stack+0xb0/0xe4)
    [<c047fec8>] (dump_stack) from [<c010dcfc>] (smp_cross_call+0xbc/0x188)
    [<c010dcfc>] (smp_cross_call) from [<c01c9e28>] (generic_exec_single+0x9c/0x15c)
    [<c01c9e28>] (generic_exec_single) from [<c01ca0a0>] (smp_call_function_single_async+0 x38/0x9c)
    [<c01ca0a0>] (smp_call_function_single_async) from [<c0603728>] (cpuidle_coupled_poke_others+0x8c/0xa8)
    [<c0603728>] (cpuidle_coupled_poke_others) from [<c0603c10>] (cpuidle_enter_state_coupled+0x26c/0x390)
    [<c0603c10>] (cpuidle_enter_state_coupled) from [<c0183c74>] (cpu_startup_entry+0x198/0x3a0)
    [<c0183c74>] (cpu_startup_entry) from [<c0b00c0c>] (start_kernel+0x354/0x3c8)
    [<c0b00c0c>] (start_kernel) from [<8000807c>] (0x8000807c)
    
    ------------------------------------------------------------------------
    Reported-by: default avatarTony Lindgren <tony@atomide.com>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Tested-by: default avatarTony Lindgren <tony@atomide.com>
    Tested-by: default avatarGuenter Roeck <linux@roeck-us.net>
    Cc: Russell King <linux@arm.linux.org.uk>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: <linux-omap@vger.kernel.org>
    Cc: <linux-arm-kernel@lists.infradead.org>
    7c64cc05
smp.c 17.1 KB