gic_raise_softirq() walks the list of cpus using for_each_cpu(), it calls
gic_compute_target_list() which advances the iterator by the number of
CPUs in the cluster.
If gic_compute_target_list() reaches the last CPU it leaves the iterator
pointing at the last CPU. This means the next time round the for_each_cpu()
loop cpumask_next() will be called with an invalid CPU.
This triggers a warning when built with CONFIG_DEBUG_PER_CPU_MAPS:
[ 3.077738] GICv3: CPU1: found redistributor 1 region 0:0x000000002f120000
[ 3.077943] CPU1: Booted secondary processor [410fd0f0]
[ 3.078542] ------------[ cut here ]------------
[ 3.078746] WARNING: CPU: 1 PID: 0 at ../include/linux/cpumask.h:121 gic_raise_softirq+0x12c/0x170
[ 3.078812] Modules linked in:
[ 3.078869]
[ 3.078930] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.8.0-rc5+ #5188
[ 3.078994] Hardware name: Foundation-v8A (DT)
[ 3.079059] task: ffff80087a1a0080 task.stack: ffff80087a19c000
[ 3.079145] PC is at gic_raise_softirq+0x12c/0x170
[ 3.079226] LR is at gic_raise_softirq+0xa4/0x170
[ 3.079296] pc : [<ffff0000083ead24>] lr : [<ffff0000083eac9c>] pstate: 200001c9
[ 3.081139] Call trace:
[ 3.081202] Exception stack(0xffff80087a19fbe0 to 0xffff80087a19fd10)
[ 3.082269] [<ffff0000083ead24>] gic_raise_softirq+0x12c/0x170
[ 3.082354] [<ffff00000808e614>] smp_send_reschedule+0x34/0x40
[ 3.082433] [<ffff0000080e80a0>] resched_curr+0x50/0x88
[ 3.082512] [<ffff0000080e89d0>] check_preempt_curr+0x60/0xd0
[ 3.082593] [<ffff0000080e8a60>] ttwu_do_wakeup+0x20/0xe8
[ 3.082672] [<ffff0000080e8bb8>] ttwu_do_activate+0x90/0xc0
[ 3.082753] [<ffff0000080ea9a4>] try_to_wake_up+0x224/0x370
[ 3.082836] [<ffff0000080eabc8>] default_wake_function+0x10/0x18
[ 3.082920] [<ffff000008103134>] __wake_up_common+0x5c/0xa0
[ 3.083003] [<ffff0000081031f4>] __wake_up_locked+0x14/0x20
[ 3.083086] [<ffff000008103f80>] complete+0x40/0x60
[ 3.083168] [<ffff00000808df7c>] secondary_start_kernel+0x15c/0x1d0
[ 3.083240] [<00000000808911a4>] 0x808911a4
[ 3.113401] Detected PIPT I-cache on CPU2
Avoid updating the iterator if the next call to cpumask_next() would
cause the for_each_cpu() loop to exit.
There is no change to gic_raise_softirq()'s behaviour, (cpumask_next()s
eventual call to _find_next_bit() will return early as start >= nbits),
this patch just silences the warning.
Fixes: 021f653791 ("irqchip: gic-v3: Initial support for GICv3")
Signed-off-by: James Morse <james.morse@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1474306155-3303-1-git-send-email-james.morse@arm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
727653d6ce