[Xen-changelog] [xen staging] rcu: add assertions to debug build

[patchbot@xxxxxxx]

commit a6fe79a5979a64c86ed5e60715ddfe5090bf1963
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Thu Mar 26 12:46:48 2020 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 26 12:46:48 2020 +0100

    rcu: add assertions to debug build
    
    Xen's RCU implementation relies on no softirq handling taking place
    while being in a RCU critical section. Add ASSERT()s in debug builds
    in order to catch any violations.
    
    For that purpose modify rcu_read_[un]lock() to use a dedicated percpu
    counter additional to preempt_[en|dis]able() as this enables to test
    that condition in __do_softirq() (ASSERT_NOT_IN_ATOMIC() is not
    usable there due to __cpu_up() calling process_pending_softirqs()
    while holding the cpu hotplug lock).
    
    While at it switch the rcu_read_[un]lock() implementation to static
    inline functions instead of macros.
    
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/rcupdate.c      |  2 ++
 xen/common/softirq.c       |  4 +++-
 xen/include/xen/rcupdate.h | 37 ++++++++++++++++++++++++++++++++++---
 3 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/xen/common/rcupdate.c b/xen/common/rcupdate.c
index f3159e470f..a5a27af3de 100644
--- a/xen/common/rcupdate.c
+++ b/xen/common/rcupdate.c
@@ -46,6 +46,8 @@
 #include <xen/cpu.h>
 #include <xen/stop_machine.h>
 
+DEFINE_PER_CPU(unsigned int, rcu_lock_cnt);
+
 /* Global control variables for rcupdate callback mechanism. */
 static struct rcu_ctrlblk {
     long cur;           /* Current batch number.                      */
diff --git a/xen/common/softirq.c b/xen/common/softirq.c
index 00d676b62c..eba65c5fc0 100644
--- a/xen/common/softirq.c
+++ b/xen/common/softirq.c
@@ -31,6 +31,8 @@ static void __do_softirq(unsigned long ignore_mask)
     unsigned long pending;
     bool rcu_allowed = !(ignore_mask & (1ul << RCU_SOFTIRQ));
 
+    ASSERT(!rcu_allowed || rcu_quiesce_allowed());
+
     for ( ; ; )
     {
         /*
@@ -58,7 +60,7 @@ void process_pending_softirqs(void)
                                 (1ul << SCHED_SLAVE_SOFTIRQ);
 
     /* Block RCU processing in case of rcu_read_lock() held. */
-    if ( preempt_count() )
+    if ( !rcu_quiesce_allowed() )
         ignore_mask |= 1ul << RCU_SOFTIRQ;
 
     ASSERT(!in_irq() && local_irq_is_enabled());
diff --git a/xen/include/xen/rcupdate.h b/xen/include/xen/rcupdate.h
index 31c8b86d13..6f2587058e 100644
--- a/xen/include/xen/rcupdate.h
+++ b/xen/include/xen/rcupdate.h
@@ -32,12 +32,35 @@
 #define __XEN_RCUPDATE_H
 
 #include <xen/cache.h>
+#include <xen/compiler.h>
 #include <xen/spinlock.h>
 #include <xen/cpumask.h>
+#include <xen/percpu.h>
 #include <xen/preempt.h>
 
 #define __rcu
 
+DECLARE_PER_CPU(unsigned int, rcu_lock_cnt);
+
+static inline void rcu_quiesce_disable(void)
+{
+    preempt_disable();
+    this_cpu(rcu_lock_cnt)++;
+    barrier();
+}
+
+static inline void rcu_quiesce_enable(void)
+{
+    barrier();
+    this_cpu(rcu_lock_cnt)--;
+    preempt_enable();
+}
+
+static inline bool rcu_quiesce_allowed(void)
+{
+    return !this_cpu(rcu_lock_cnt);
+}
+
 /**
  * struct rcu_head - callback structure for use with RCU
  * @next: next update requests in a list
@@ -91,16 +114,24 @@ typedef struct _rcu_read_lock rcu_read_lock_t;
  * will be deferred until the outermost RCU read-side critical section
  * completes.
  *
- * It is illegal to block while in an RCU read-side critical section.
+ * It is illegal to process softirqs or block while in an RCU read-side
+ * critical section.
  */
-#define rcu_read_lock(x)       ({ ((void)(x)); preempt_disable(); })
+static inline void rcu_read_lock(rcu_read_lock_t *lock)
+{
+    rcu_quiesce_disable();
+}
 
 /**
  * rcu_read_unlock - marks the end of an RCU read-side critical section.
  *
  * See rcu_read_lock() for more information.
  */
-#define rcu_read_unlock(x)     ({ ((void)(x)); preempt_enable(); })
+static inline void rcu_read_unlock(rcu_read_lock_t *lock)
+{
+    ASSERT(!rcu_quiesce_allowed());
+    rcu_quiesce_enable();
+}
 
 /*
  * So where is rcu_write_lock()?  It does not exist, as there is no
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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