linux.git/include/linux/hardirq.h, branch v7.3-rc2

preempt: Introduce HAS_SEPARATE_PREEMPT_RESCHED_BITS

2026-08-10T08:50:19+00:00

With the changes that enable preempt count to track IRQ disabling
nesting, we don't have enough bits in 32-bit preempt count
implementation, as a result we move NMI nesting bits out of the 32-bit
preempt count. However on the architectures that can support 64-bit
preempt count implementation, we can keep the NMI nesting bits in the
32-bit preempt count and avoid maintaining NMI nesting bits outside of
the same cache line.

Therefore HAS_SEPARATE_PREEMPT_RESCHED_BITS is introduced to allow
architectures to select this. Note that under this Kconfig, preempt
count is maintained in a 64-bit word however preempt_count() still
remains as an int because all the effective bits still fit in
(previously we mask out NEED_RESCHED bit in preempt_count()). This
should make no functional changes for existing preempt_count() users.

Enable this for x86_64 along with the introduction of the Kconfig.

[boqun: Undo the __preempt_count_{add,sub}() optimization in 32-bit
preempt count since it may introduce {over,under}flow]

Originally-by: Peter Zijlstra 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://patch.msgid.link/20260804161447.84806-11-boqun@kernel.org

preempt: Track NMI nesting to separate per-CPU counter

2026-08-08T20:44:05+00:00

Move NMI nesting tracking from the preempt_count bits to a separate
per-CPU counter (nmi_nesting). This is to free up the NMI bits in the
preempt_count, allowing those bits to be repurposed for other uses.

Reduce NMI_BITS from 4 to 1, using it only to detect if we're in an NMI.
The per-CPU counter currently caps nesting at 15.

[boqun: Address Steven Rostedt's comment on the BUG_ON() condition]
[boqun: Use preempt_count_set() in __nmi_exit() to avoid underflow]

Suggested-by: Boqun Feng 
Signed-off-by: Joel Fernandes 
Signed-off-by: Lyude Paul 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://patch.msgid.link/20260121223933.1568682-3-lyude@redhat.com
Link: https://patch.msgid.link/20260804161447.84806-2-boqun@kernel.org

rcu/context-tracking: Remove unused and/or unecessary middle functions

2022-07-05T20:33:00+00:00

Some eqs functions are now only used internally by context tracking, so
their public declarations can be removed.

Also middle functions such as rcu_user_*() and rcu_idle_*()
which now directly call to rcu_eqs_enter() and rcu_eqs_exit() can be
wiped out as well.

Signed-off-by: Frederic Weisbecker 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Neeraj Upadhyay 
Cc: Uladzislau Rezki 
Cc: Joel Fernandes 
Cc: Boqun Feng 
Cc: Nicolas Saenz Julienne 
Cc: Marcelo Tosatti 
Cc: Xiongfeng Wang 
Cc: Yu Liao 
Cc: Phil Auld 
Cc: Paul Gortmaker
Cc: Alex Belits 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Nicolas Saenz Julienne 
Tested-by: Nicolas Saenz Julienne

context_tracking: Take NMI eqs entrypoints over RCU

2022-07-05T20:32:59+00:00

The RCU dynticks counter is going to be merged into the context tracking
subsystem. Prepare with moving the NMI extended quiescent states
entrypoints to context tracking. For now those are dumb redirection to
existing RCU calls.

Acked-by: Paul E. McKenney 
Signed-off-by: Frederic Weisbecker 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Neeraj Upadhyay 
Cc: Uladzislau Rezki 
Cc: Joel Fernandes 
Cc: Boqun Feng 
Cc: Nicolas Saenz Julienne 
Cc: Marcelo Tosatti 
Cc: Xiongfeng Wang 
Cc: Yu Liao 
Cc: Phil Auld 
Cc: Paul Gortmaker
Cc: Alex Belits 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Nicolas Saenz Julienne 
Tested-by: Nicolas Saenz Julienne

printk: remove NMI tracking

2021-07-26T13:09:44+00:00

All NMI contexts are handled the same as the safe context: store the
message and defer printing. There is no need to have special NMI
context tracking for this. Using in_nmi() is enough.

There are several parts of the kernel that are manually calling into
the printk NMI context tracking in order to cause general printk
deferred printing:

    arch/arm/kernel/smp.c
    arch/powerpc/kexec/crash.c
    kernel/trace/trace.c

For arm/kernel/smp.c and powerpc/kexec/crash.c, provide a new
function pair printk_deferred_enter/exit that explicitly achieves the
same objective.

For ftrace, remove the printk context manipulation completely. It was
added in commit 03fc7f9c99c1 ("printk/nmi: Prevent deadlock when
accessing the main log buffer in NMI"). The purpose was to enforce
storing messages directly into the ring buffer even in NMI context.
It really should have only modified the behavior in NMI context.
There is no need for a special behavior any longer. All messages are
always stored directly now. The console deferring is handled
transparently in vprintk().

Signed-off-by: John Ogness 
[pmladek@suse.com: Remove special handling in ftrace.c completely.
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20210715193359.25946-5-john.ogness@linutronix.de

softirq: Add RT specific softirq accounting

2021-03-17T15:34:08+00:00

RT requires the softirq processing and local bottomhalf disabled regions to
be preemptible. Using the normal preempt count based serialization is
therefore not possible because this implicitely disables preemption.

RT kernels use a per CPU local lock to serialize bottomhalfs. As
local_bh_disable() can nest the lock can only be acquired on the outermost
invocation of local_bh_disable() and released when the nest count becomes
zero. Tasks which hold the local lock can be preempted so its required to
keep track of the nest count per task.

Add a RT only counter to task struct and adjust the relevant macros in
preempt.h.

Signed-off-by: Thomas Gleixner 
Tested-by: Sebastian Andrzej Siewior 
Tested-by: Paul E. McKenney 
Reviewed-by: Frederic Weisbecker 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20210309085726.983627589@linutronix.de

irqtime: Move irqtime entry accounting after irq offset incrementation

2020-12-02T19:20:05+00:00

IRQ time entry is currently accounted before HARDIRQ_OFFSET or
SOFTIRQ_OFFSET are incremented. This is convenient to decide to which
index the cputime to account is dispatched.

Unfortunately it prevents tick_irq_enter() from being called under
HARDIRQ_OFFSET because tick_irq_enter() has to be called before the IRQ
entry accounting due to the necessary clock catch up. As a result we
don't benefit from appropriate lockdep coverage on tick_irq_enter().

To prepare for fixing this, move the IRQ entry cputime accounting after
the preempt offset is incremented. This requires the cputime dispatch
code to handle the extra offset.

Signed-off-by: Frederic Weisbecker 
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20201202115732.27827-5-frederic@kernel.org

x86/entry: Fix NMI vs IRQ state tracking

2020-07-10T10:00:01+00:00

While the nmi_enter() users did
trace_hardirqs_{off_prepare,on_finish}() there was no matching
lockdep_hardirqs_*() calls to complete the picture.

Introduce idtentry_{enter,exit}_nmi() to enable proper IRQ state
tracking across the NMIs.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Ingo Molnar 
Link: https://lkml.kernel.org/r/20200623083721.216740948@infradead.org

genirq: Provide __irq_enter/exit_raw()

2020-06-11T13:15:06+00:00

Like __irq_enter/exit() but without time accounting. To be used for "empty"
system vectors like the scheduler IPI to avoid the overhead.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Ingo Molnar 
Reviewed-by: Andy Lutomirski 
Link: https://lore.kernel.org/r/20200521202117.671682341@linutronix.de

genirq: Provide irq_enter/exit_rcu()

2020-06-11T13:15:06+00:00

irq_enter()/exit() currently include RCU handling. To properly separate the RCU
handling code, provide variants which contain only the non-RCU related
functionality.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Ingo Molnar 
Reviewed-by: Andy Lutomirski 
Link: https://lore.kernel.org/r/20200521202117.567023613@linutronix.de