srcu: Create CPP macros for normal and NMI-safe SRCU readers

This commit creates SRCU_READ_FLAVOR_NORMAL and SRCU_READ_FLAVOR_NMI
C-preprocessor macros for srcu_read_lock() and srcu_read_lock_nmisafe(),
respectively.  These replace the old true/false values that were
previously passed to srcu_check_read_flavor().  In addition, the
srcu_check_read_flavor() function itself requires a bit of rework to
handle bitmasks instead of true/false values.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 46fd06b212baa5136d4135e1c71267f12c410e31..84daaa33ea0abf4301efd7f0bb7805b828372423 100644 (file)
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -176,10 +176,6 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp)
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
-#define SRCU_NMI_UNKNOWN       0x0
-#define SRCU_NMI_UNSAFE                0x1
-#define SRCU_NMI_SAFE          0x2
-
 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)
 void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor);
 #else
@@ -247,7 +243,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
 {
        int retval;
 
-       srcu_check_read_flavor(ssp, false);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
        retval = __srcu_read_lock(ssp);
        srcu_lock_acquire(&ssp->dep_map);
        return retval;
@@ -268,7 +264,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp
 {
        int retval;
 
-       srcu_check_read_flavor(ssp, true);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
        retval = __srcu_read_lock_nmisafe(ssp);
        rcu_try_lock_acquire(&ssp->dep_map);
        return retval;
@@ -280,7 +276,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
 {
        int retval;
 
-       srcu_check_read_flavor(ssp, false);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
        retval = __srcu_read_lock(ssp);
        return retval;
 }
@@ -309,7 +305,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
 static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
 {
        WARN_ON_ONCE(in_nmi());
-       srcu_check_read_flavor(ssp, false);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
        return __srcu_read_lock(ssp);
 }
 
@@ -324,7 +320,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
        __releases(ssp)
 {
        WARN_ON_ONCE(idx & ~0x1);
-       srcu_check_read_flavor(ssp, false);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
        srcu_lock_release(&ssp->dep_map);
        __srcu_read_unlock(ssp, idx);
 }
@@ -340,7 +336,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
        __releases(ssp)
 {
        WARN_ON_ONCE(idx & ~0x1);
-       srcu_check_read_flavor(ssp, true);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
        rcu_lock_release(&ssp->dep_map);
        __srcu_read_unlock_nmisafe(ssp, idx);
 }
@@ -349,7 +345,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
 static inline notrace void
 srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
 {
-       srcu_check_read_flavor(ssp, false);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
        __srcu_read_unlock(ssp, idx);
 }
 
@@ -366,7 +362,7 @@ static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
 {
        WARN_ON_ONCE(idx & ~0x1);
        WARN_ON_ONCE(in_nmi());
-       srcu_check_read_flavor(ssp, false);
+       srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
        __srcu_read_unlock(ssp, idx);
 }
 

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index ab7d8d215b84ba343d763a168d171eb9e2716dac..79ad809c7f03556899970d8349ffe8ce497f6753 100644 (file)
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -43,6 +43,10 @@ struct srcu_data {
        struct srcu_struct *ssp;
 };
 
+/* Values for ->srcu_reader_flavor. */
+#define SRCU_READ_FLAVOR_NORMAL        0x1             // srcu_read_lock().
+#define SRCU_READ_FLAVOR_NMI   0x2             // srcu_read_lock_nmisafe().
+
 /*
  * Node in SRCU combining tree, similar in function to rcu_data.
  */

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index b85da944d794a5cb8b850c7eabdaa6fa5a97ee26..602b4b8c4b8910ded74ff1ee014f56889d2ccb31 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -463,7 +463,7 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
                        mask = mask | READ_ONCE(sdp->srcu_reader_flavor);
        }
        WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)),
-                 "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
+                 "Mixed reader flavors for srcu_struct at %ps.\n", ssp);
        return sum;
 }
 
@@ -703,20 +703,21 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
  */
 void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
 {
-       int reader_flavor_mask = 1 << read_flavor;
-       int old_reader_flavor_mask;
+       int old_read_flavor;
        struct srcu_data *sdp;
 
-       /* NMI-unsafe use in NMI is a bad sign */
-       WARN_ON_ONCE(!read_flavor && in_nmi());
+       /* NMI-unsafe use in NMI is a bad sign, as is multi-bit read_flavor values. */
+       WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi());
+       WARN_ON_ONCE(read_flavor & (read_flavor - 1));
+
        sdp = raw_cpu_ptr(ssp->sda);
-       old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor);
-       if (!old_reader_flavor_mask) {
-               old_reader_flavor_mask = cmpxchg(&sdp->srcu_reader_flavor, 0, reader_flavor_mask);
-               if (!old_reader_flavor_mask)
+       old_read_flavor = READ_ONCE(sdp->srcu_reader_flavor);
+       if (!old_read_flavor) {
+               old_read_flavor = cmpxchg(&sdp->srcu_reader_flavor, 0, read_flavor);
+               if (!old_read_flavor)
                        return;
        }
-       WARN_ONCE(old_reader_flavor_mask != reader_flavor_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_reader_flavor_mask, reader_flavor_mask);
+       WARN_ONCE(old_read_flavor != read_flavor, "CPU %d old state %d new state %d\n", sdp->cpu, old_read_flavor, read_flavor);
 }
 EXPORT_SYMBOL_GPL(srcu_check_read_flavor);
 #endif /* CONFIG_PROVE_RCU */