Revert "workqueue: consider work function when searching for busy work items"

This reverts commit 9a621726d1c139db28b6a434c236ad55cea95010.
Revert "mm/swapfile.c: do not skip lowest_bit in scan_swap_map() scan loop"

This reverts commit 09c8ac4e646ae2df8afe3cf1974dd87a66980432.
mm/swapfile.c: do not skip lowest_bit in scan_swap_map() scan loop

In the second half of scan_swap_map()'s scan loop, offset is set to
si->lowest_bit and then incremented before entering the loop for the
first time, causing si->swap_map[si->lowest_bit] to be skipped.

Signed-off-by: Jamie Liu <jamieliu@google.com>
Cc: Shaohua Li <shli@fusionio.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: Remove get_online_cpus() usage

Remove get_online_cpus() usage from the scheduler; there's 4 sites that
use it:

 - sched_init_smp(); where its completely superfluous since we're in
   'early' boot and there simply cannot be any hotplugging.

 - sched_getaffinity(); we already take a raw spinlock to protect the
   task cpus_allowed mask, this disables preemption and therefore
   also stabilizes cpu_online_mask as that's modified using
   stop_machine. However switch to active mask for symmetry with
   sched_setaffinity()/set_cpus_allowed_ptr(). We guarantee active
   mask stability by inserting sync_rcu/sched() into _cpu_down.

 - sched_setaffinity(); we don't appear to need get_online_cpus()
   either, there's two sites where hotplug appears relevant:
    * cpuset_cpus_allowed(); for the !cpuset case we use possible_mask,
      for the cpuset case we hold task_lock, which is a spinlock and
      thus for mainline disables preemption (might cause pain on RT).
    * set_cpus_allowed_ptr(); Holds all scheduler locks and thus has
      preemption properly disabled; also it already deals with hotplug
      races explicitly where it releases them.

 - migrate_swap(); we can make stop_two_cpus() do the heavy lifting for
   us with a little trickery. By adding a sync_sched/rcu() after the
   CPU_DOWN_PREPARE notifier we can provide preempt/rcu guarantees for
   cpu_active_mask. Use these to validate that both our cpus are active
   when queueing the stop work before we queue the stop_machine works
   for take_cpu_down().

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[kaushalk@codeaurora.org: get_online_cpus has only 3 sites of usage in
 kernel/sched/core.c of msm-3.10 so migrate_swap changes are not
 applicable here. stop_two_cpus related change is not applicable to
 msm-3.10, so skip it.]
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: Fix endless sync_sched/rcu() loop inside _cpu_down()

Commit bbe68f8267e290ef4c752b84833b6222bc2ce60b:

	sched: Remove get_online_cpus() usage

tries to do sync_sched/rcu() inside _cpu_down() but triggers:

	INFO: task swapper/0:1 blocked for more than 120 seconds.
	...
	[<ffffffff811263dc>] synchronize_rcu+0x2c/0x30
	[<ffffffff81d1bd82>] _cpu_down+0x2b2/0x340
	...

It was caused by that in the rcu boost case we rely on smpboot thread to
finish the rcu callback, which has already been parked before sync in here
and leads to the endless sync_sched/rcu().

This patch exchanges the sequence of smpboot_park_threads() and
sync_sched/rcu() to fix the bug.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: Remove extra put_online_cpus() inside sched_setaffinity()

Commit bbe68f8267e290ef4c752b84833b6222bc2ce60b:

	sched: Remove get_online_cpus() usage

has left one extra put_online_cpus() inside sched_setaffinity(),
remove it to fix the WARN:

   ------------[ cut here ]------------
   WARNING: CPU: 0 PID: 3166 at kernel/cpu.c:84 put_online_cpus+0x43/0x70()
   ...
   [<ffffffff810c3fef>] put_online_cpus+0x43/0x70 [
   [<ffffffff810efd59>] sched_setaffinity+0x7d/0x1f9 [
   ...

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: Remove get_online_cpus() usage

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: core: Add some info bits

* No functional changes.

Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

Conflicts:
	kernel/sched/core.c
irq: Ensure irq_exit() code runs with interrupts disabled

We had already a few problems with code called from irq_exit() when
interrupted from a nesting interrupt. This can happen on architectures
which do not define __ARCH_IRQ_EXIT_IRQS_DISABLED.

__ARCH_IRQ_EXIT_IRQS_DISABLED should go away and we want to make it
mandatory to call irq_exit() with interrupts disabled.

As a temporary protection disable interrupts for those architectures
which do not define __ARCH_IRQ_EXIT_IRQS_DISABLED and add a WARN_ONCE
when an architecture which defines __ARCH_IRQ_EXIT_IRQS_DISABLED calls
irq_exit() with interrupts enabled.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Sanitize invoke_softirq

With the irq protection in irq_exit, we can remove the #ifdeffery and
the bh_disable/enable dance in invoke_softirq()

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Remove IRQ_EXIT_OFFSET workaround

The IRQ_EXIT_OFFSET trick was used to make sure the irq
doesn't get preempted after we substract the HARDIRQ_OFFSET
until we are entirely done with any code in irq_exit().

This workaround was necessary because some archs may call
irq_exit() with irqs enabled and there is still some code
in the end of this function that is not covered by the
HARDIRQ_OFFSET but want to stay non-preemptible.

Now that irq are always disabled in irq_exit(), the whole code
is guaranteed not to be preempted. We can thus remove this hack.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Don't re-enable interrupts at the end of irq_exit

Commit "irq: Ensure irq_exit() code runs with interrupts disabled"
restore interrupts flags in the end of irq_exit() for archs
that don't define __ARCH_IRQ_EXIT_IRQS_DISABLED.

However always returning from irq_exit() with interrupts
disabled should not be a problem for these archs. Prior to
this commit this was already happening anytime we processed
pending softirqs anyway.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Fix lockup related to stop_machine being stuck in __do_softirq.

The stop machine logic can lock up if all but one of the migration
threads make it through the disable-irq step and the one remaining
thread gets stuck in __do_softirq.  The reason __do_softirq can hang is
that it has a bail-out based on jiffies timeout, but in the lockup case,
jiffies itself is not incremented.

To work around this, re-add the max_restart counter in __do_irq and stop
processing irqs after 10 restarts.

Thanks to Tejun Heo and Rusty Russell and others for helping me track
this down.

This was introduced in 3.9 by commit ("softirq: reduce latencies").

It may be worth looking into ath9k to see if it has issues with its irq
handler at a later date.

The hang stack traces look something like this:

    ------------[ cut here ]------------
    WARNING: at kernel/watchdog.c:245 watchdog_overflow_callback+0x9c/0xa7()
    Watchdog detected hard LOCKUP on cpu 2
    Modules linked in: ath9k ath9k_common ath9k_hw ath mac80211 cfg80211 nfsv4 auth_rpcgss nfs fscache nf_nat_ipv4 nf_nat veth 8021q garp stp mrp llc pktgen lockd sunrpc]
    Pid: 23, comm: migration/2 Tainted: G         C   3.9.4+ #11
    Call Trace:
     <NMI>   warn_slowpath_common+0x85/0x9f
      warn_slowpath_fmt+0x46/0x48
      watchdog_overflow_callback+0x9c/0xa7
      __perf_event_overflow+0x137/0x1cb
      perf_event_overflow+0x14/0x16
      intel_pmu_handle_irq+0x2dc/0x359
      perf_event_nmi_handler+0x19/0x1b
      nmi_handle+0x7f/0xc2
      do_nmi+0xbc/0x304
      end_repeat_nmi+0x1e/0x2e
     <<EOE>>
      cpu_stopper_thread+0xae/0x162
      smpboot_thread_fn+0x258/0x260
      kthread+0xc7/0xcf
      ret_from_fork+0x7c/0xb0
    ---[ end trace 4947dfa9b0a4cec3 ]---
    BUG: soft lockup - CPU#1 stuck for 22s! [migration/1:17]
    Modules linked in: ath9k ath9k_common ath9k_hw ath mac80211 cfg80211 nfsv4 auth_rpcgss nfs fscache nf_nat_ipv4 nf_nat veth 8021q garp stp mrp llc pktgen lockd sunrpc]
    irq event stamp: 835637905
    hardirqs last  enabled at (835637904): __do_softirq+0x9f/0x257
    hardirqs last disabled at (835637905): apic_timer_interrupt+0x6d/0x80
    softirqs last  enabled at (5654720): __do_softirq+0x1ff/0x257
    softirqs last disabled at (5654725): irq_exit+0x5f/0xbb
    CPU 1
    Pid: 17, comm: migration/1 Tainted: G        WC   3.9.4+ #11 To be filled by O.E.M. To be filled by O.E.M./To be filled by O.E.M.
    RIP: tasklet_hi_action+0xf0/0xf0
    Process migration/1
    Call Trace:
     <IRQ>
      __do_softirq+0x117/0x257
      irq_exit+0x5f/0xbb
      smp_apic_timer_interrupt+0x8a/0x98
      apic_timer_interrupt+0x72/0x80
     <EOI>
      printk+0x4d/0x4f
      stop_machine_cpu_stop+0x22c/0x274
      cpu_stopper_thread+0xae/0x162
      smpboot_thread_fn+0x258/0x260
      kthread+0xc7/0xcf
      ret_from_fork+0x7c/0xb0

Signed-off-by: Ben Greear <greearb@candelatech.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Pekka Riikonen <priikone@iki.fi>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Force hardirq exit's softirq processing on its own stack

The commit facd8b80c67a3cf64a467c4a2ac5fb31f2e6745b
("irq: Sanitize invoke_softirq") converted irq exit
calls of do_softirq() to __do_softirq() on all architectures,
assuming it was only used there for its irq disablement
properties.

But as a side effect, the softirqs processed in the end
of the hardirq are always called on the inline current
stack that is used by irq_exit() instead of the softirq
stack provided by the archs that override do_softirq().

The result is mostly safe if the architecture runs irq_exit()
on a separate irq stack because then softirqs are processed
on that same stack that is near empty at this stage (assuming
hardirq aren't nesting).

Otherwise irq_exit() runs in the task stack and so does the softirq
too. The interrupted call stack can be randomly deep already and
the softirq can dig through it even further. To add insult to the
injury, this softirq can be interrupted by a new hardirq, maximizing
the chances for a stack overrun as reported in powerpc for example:

	do_IRQ: stack overflow: 1920
	CPU: 0 PID: 1602 Comm: qemu-system-ppc Not tainted 3.10.4-300.1.fc19.ppc64p7 #1
	Call Trace:
	[c0000000050a8740] .show_stack+0x130/0x200 (unreliable)
	[c0000000050a8810] .dump_stack+0x28/0x3c
	[c0000000050a8880] .do_IRQ+0x2b8/0x2c0
	[c0000000050a8930] hardware_interrupt_common+0x154/0x180
	--- Exception: 501 at .cp_start_xmit+0x3a4/0x820 [8139cp]
		LR = .cp_start_xmit+0x390/0x820 [8139cp]
	[c0000000050a8d40] .dev_hard_start_xmit+0x394/0x640
	[c0000000050a8e00] .sch_direct_xmit+0x110/0x260
	[c0000000050a8ea0] .dev_queue_xmit+0x260/0x630
	[c0000000050a8f40] .br_dev_queue_push_xmit+0xc4/0x130 [bridge]
	[c0000000050a8fc0] .br_dev_xmit+0x198/0x270 [bridge]
	[c0000000050a9070] .dev_hard_start_xmit+0x394/0x640
	[c0000000050a9130] .dev_queue_xmit+0x428/0x630
	[c0000000050a91d0] .ip_finish_output+0x2a4/0x550
	[c0000000050a9290] .ip_local_out+0x50/0x70
	[c0000000050a9310] .ip_queue_xmit+0x148/0x420
	[c0000000050a93b0] .tcp_transmit_skb+0x4e4/0xaf0
	[c0000000050a94a0] .__tcp_ack_snd_check+0x7c/0xf0
	[c0000000050a9520] .tcp_rcv_established+0x1e8/0x930
	[c0000000050a95f0] .tcp_v4_do_rcv+0x21c/0x570
	[c0000000050a96c0] .tcp_v4_rcv+0x734/0x930
	[c0000000050a97a0] .ip_local_deliver_finish+0x184/0x360
	[c0000000050a9840] .ip_rcv_finish+0x148/0x400
	[c0000000050a98d0] .__netif_receive_skb_core+0x4f8/0xb00
	[c0000000050a99d0] .netif_receive_skb+0x44/0x110
	[c0000000050a9a70] .br_handle_frame_finish+0x2bc/0x3f0 [bridge]
	[c0000000050a9b20] .br_nf_pre_routing_finish+0x2ac/0x420 [bridge]
	[c0000000050a9bd0] .br_nf_pre_routing+0x4dc/0x7d0 [bridge]
	[c0000000050a9c70] .nf_iterate+0x114/0x130
	[c0000000050a9d30] .nf_hook_slow+0xb4/0x1e0
	[c0000000050a9e00] .br_handle_frame+0x290/0x330 [bridge]
	[c0000000050a9ea0] .__netif_receive_skb_core+0x34c/0xb00
	[c0000000050a9fa0] .netif_receive_skb+0x44/0x110
	[c0000000050aa040] .napi_gro_receive+0xe8/0x120
	[c0000000050aa0c0] .cp_rx_poll+0x31c/0x590 [8139cp]
	[c0000000050aa1d0] .net_rx_action+0x1dc/0x310
	[c0000000050aa2b0] .__do_softirq+0x158/0x330
	[c0000000050aa3b0] .irq_exit+0xc8/0x110
	[c0000000050aa430] .do_IRQ+0xdc/0x2c0
	[c0000000050aa4e0] hardware_interrupt_common+0x154/0x180
	 --- Exception: 501 at .bad_range+0x1c/0x110
		 LR = .get_page_from_freelist+0x908/0xbb0
	[c0000000050aa7d0] .list_del+0x18/0x50 (unreliable)
	[c0000000050aa850] .get_page_from_freelist+0x908/0xbb0
	[c0000000050aa9e0] .__alloc_pages_nodemask+0x21c/0xae0
	[c0000000050aaba0] .alloc_pages_vma+0xd0/0x210
	[c0000000050aac60] .handle_pte_fault+0x814/0xb70
	[c0000000050aad50] .__get_user_pages+0x1a4/0x640
	[c0000000050aae60] .get_user_pages_fast+0xec/0x160
	[c0000000050aaf10] .__gfn_to_pfn_memslot+0x3b0/0x430 [kvm]
	[c0000000050aafd0] .kvmppc_gfn_to_pfn+0x64/0x130 [kvm]
	[c0000000050ab070] .kvmppc_mmu_map_page+0x94/0x530 [kvm]
	[c0000000050ab190] .kvmppc_handle_pagefault+0x174/0x610 [kvm]
	[c0000000050ab270] .kvmppc_handle_exit_pr+0x464/0x9b0 [kvm]
	[c0000000050ab320]  kvm_start_lightweight+0x1ec/0x1fc [kvm]
	[c0000000050ab4f0] .kvmppc_vcpu_run_pr+0x168/0x3b0 [kvm]
	[c0000000050ab9c0] .kvmppc_vcpu_run+0xc8/0xf0 [kvm]
	[c0000000050aba50] .kvm_arch_vcpu_ioctl_run+0x5c/0x1a0 [kvm]
	[c0000000050abae0] .kvm_vcpu_ioctl+0x478/0x730 [kvm]
	[c0000000050abc90] .do_vfs_ioctl+0x4ec/0x7c0
	[c0000000050abd80] .SyS_ioctl+0xd4/0xf0
	[c0000000050abe30] syscall_exit+0x0/0x98

Since this is a regression, this patch proposes a minimalistic
and low-risk solution by blindly forcing the hardirq exit processing of
softirqs on the softirq stack. This way we should reduce significantly
the opportunities for task stack overflow dug by softirqs.

Longer term solutions may involve extending the hardirq stack coverage to
irq_exit(), etc...

Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: #3.9.. <stable@vger.kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Consolidate do_softirq() arch overriden implementations

All arch overriden implementations of do_softirq() share the following
common code: disable irqs (to avoid races with the pending check),
check if there are softirqs pending, then execute __do_softirq() on
a specific stack.

Consolidate the common parts such that archs only worry about the
stack switch.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

Conflicts:
	kernel/softirq.c
irq: Optimize call to softirq on hardirq exit

Before processing softirqs on hardirq exit, we already
do the check for pending softirqs while hardirqs are
guaranteed to be disabled.

So we can take a shortcut and safely jump to the arch
specific implementation directly.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Improve a bit softirq debugging

do_softirq() has a debug check that verifies that it is not nesting
on softirqs processing, nor miscounting the softirq part of the preempt
count.

But making sure that softirqs processing don't nest is actually a more
generic concern that applies to any caller of __do_softirq().

Do take it one step further and generalize that debug check to
any softirq processing.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Justify the various softirq stack choices

For clarity, comment the various stack choices for softirqs
processing, whether we execute them from ksoftirqd or
local_irq_enable() calls.

Their use on irq_exit() is already commented.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
irq: Optimize softirq stack selection in irq exit

If irq_exit() is called on the arch's specified irq stack,
it should be safe to run softirqs inline under that same
irq stack as it is near empty by the time we call irq_exit().

For example if we use the same stack for both hard and soft irqs here,
the worst case scenario is:
hardirq -> softirq -> hardirq. But then the softirq supersedes the
first hardirq as the stack user since irq_exit() is called in
a mostly empty stack. So the stack merge in this case looks acceptable.

Stack overrun still have a chance to happen if hardirqs have more
opportunities to nest, but then it's another problem to solve.

So lets adapt the irq exit's softirq stack on top of a new Kconfig symbol
that can be defined when irq_exit() runs on the irq stack. That way
we can spare some stack switch on irq processing and all the cache
issues that come along.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@au1.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
sched: Introduce preempt_count accessor functions

Replace the single preempt_count() 'function' that's an lvalue with
two proper functions:

 preempt_count() - returns the preempt_count value as rvalue
 preempt_count_set() - Allows setting the preempt-count value

Also provide preempt_count_ptr() as a convenience wrapper to implement
all modifying operations.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>