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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-09-25 15:22:31 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-09-25 15:22:31 -0700 |
| commit | ac0a36461f5316ad98e8d7dd7d1cdaf000256a9b (patch) | |
| tree | b385a44ff05008d8a4de8c079942f253c425d77b /kernel/rcu | |
| parent | e19b205be43d11bff638cad4487008c48d21c103 (diff) | |
| parent | 15516c89acce948debc4c598e03c3fee53045797 (diff) | |
Merge tag 'trace-v4.14-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing fixes from Steven Rostedt:
"Stack tracing and RCU has been having issues with each other and
lockdep has been pointing out constant problems.
The changes have been going into the stack tracer, but it has been
discovered that the problem isn't with the stack tracer itself, but it
is with calling save_stack_trace() from within the internals of RCU.
The stack tracer is the one that can trigger the issue the easiest,
but examining the problem further, it could also happen from a WARN()
in the wrong place, or even if an NMI happened in this area and it did
an rcu_read_lock().
The critical area is where RCU is not watching. Which can happen while
going to and from idle, or bringing up or taking down a CPU.
The final fix was to put the protection in kernel_text_address() as it
is the one that requires RCU to be watching while doing the stack
trace.
To make this work properly, Paul had to allow rcu_irq_enter() happen
after rcu_nmi_enter(). This should have been done anyway, since an NMI
can page fault (reading vmalloc area), and a page fault triggers
rcu_irq_enter().
One patch is just a consolidation of code so that the fix only needed
to be done in one location"
* tag 'trace-v4.14-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
tracing: Remove RCU work arounds from stack tracer
extable: Enable RCU if it is not watching in kernel_text_address()
extable: Consolidate *kernel_text_address() functions
rcu: Allow for page faults in NMI handlers
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 1250e4bd4b85..0c44c7b42e6d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -882,6 +882,11 @@ void rcu_irq_exit(void) RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!"); rdtp = this_cpu_ptr(&rcu_dynticks); + + /* Page faults can happen in NMI handlers, so check... */ + if (READ_ONCE(rdtp->dynticks_nmi_nesting)) + return; + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && rdtp->dynticks_nesting < 1); if (rdtp->dynticks_nesting <= 1) { @@ -1015,6 +1020,11 @@ void rcu_irq_enter(void) RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!"); rdtp = this_cpu_ptr(&rcu_dynticks); + + /* Page faults can happen in NMI handlers, so check... */ + if (READ_ONCE(rdtp->dynticks_nmi_nesting)) + return; + oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting++; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && |