Merge tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Thomas Gleixner:
 "A set of locking fixes and updates:

   - Untangle the header spaghetti which causes build failures in
     various situations caused by the lockdep additions to seqcount to
     validate that the write side critical sections are non-preemptible.

   - The seqcount associated lock debug addons which were blocked by the
     above fallout.

     seqcount writers contrary to seqlock writers must be externally
     serialized, which usually happens via locking - except for strict
     per CPU seqcounts. As the lock is not part of the seqcount, lockdep
     cannot validate that the lock is held.

     This new debug mechanism adds the concept of associated locks.
     sequence count has now lock type variants and corresponding
     initializers which take a pointer to the associated lock used for
     writer serialization. If lockdep is enabled the pointer is stored
     and write_seqcount_begin() has a lockdep assertion to validate that
     the lock is held.

     Aside of the type and the initializer no other code changes are
     required at the seqcount usage sites. The rest of the seqcount API
     is unchanged and determines the type at compile time with the help
     of _Generic which is possible now that the minimal GCC version has
     been moved up.

     Adding this lockdep coverage unearthed a handful of seqcount bugs
     which have been addressed already independent of this.

     While generally useful this comes with a Trojan Horse twist: On RT
     kernels the write side critical section can become preemtible if
     the writers are serialized by an associated lock, which leads to
     the well known reader preempts writer livelock. RT prevents this by
     storing the associated lock pointer independent of lockdep in the
     seqcount and changing the reader side to block on the lock when a
     reader detects that a writer is in the write side critical section.

   - Conversion of seqcount usage sites to associated types and
     initializers"

* tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
  locking/seqlock, headers: Untangle the spaghetti monster
  locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header
  x86/headers: Remove APIC headers from <asm/smp.h>
  seqcount: More consistent seqprop names
  seqcount: Compress SEQCNT_LOCKNAME_ZERO()
  seqlock: Fold seqcount_LOCKNAME_init() definition
  seqlock: Fold seqcount_LOCKNAME_t definition
  seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g
  hrtimer: Use sequence counter with associated raw spinlock
  kvm/eventfd: Use sequence counter with associated spinlock
  userfaultfd: Use sequence counter with associated spinlock
  NFSv4: Use sequence counter with associated spinlock
  iocost: Use sequence counter with associated spinlock
  raid5: Use sequence counter with associated spinlock
  vfs: Use sequence counter with associated spinlock
  timekeeping: Use sequence counter with associated raw spinlock
  xfrm: policy: Use sequence counters with associated lock
  netfilter: nft_set_rbtree: Use sequence counter with associated rwlock
  netfilter: conntrack: Use sequence counter with associated spinlock
  sched: tasks: Use sequence counter with associated spinlock
  ...

Author: torvalds

Documentation/locking/seqlock.rst

@@ -87,6 +87,58 @@ Read path::
 	} while (read_seqcount_retry(&foo_seqcount, seq));
 
 
+.. _seqcount_locktype_t:
+
+Sequence counters with associated locks (``seqcount_LOCKTYPE_t``)
+-----------------------------------------------------------------
+
+As discussed at :ref:`seqcount_t`, sequence count write side critical
+sections must be serialized and non-preemptible. This variant of
+sequence counters associate the lock used for writer serialization at
+initialization time, which enables lockdep to validate that the write
+side critical sections are properly serialized.
+
+This lock association is a NOOP if lockdep is disabled and has neither
+storage nor runtime overhead. If lockdep is enabled, the lock pointer is
+stored in struct seqcount and lockdep's "lock is held" assertions are
+injected at the beginning of the write side critical section to validate
+that it is properly protected.
+
+For lock types which do not implicitly disable preemption, preemption
+protection is enforced in the write side function.
+
+The following sequence counters with associated locks are defined:
+
+  - ``seqcount_spinlock_t``
+  - ``seqcount_raw_spinlock_t``
+  - ``seqcount_rwlock_t``
+  - ``seqcount_mutex_t``
+  - ``seqcount_ww_mutex_t``
+
+The plain seqcount read and write APIs branch out to the specific
+seqcount_LOCKTYPE_t implementation at compile-time. This avoids kernel
+API explosion per each new seqcount LOCKTYPE.
+
+Initialization (replace "LOCKTYPE" with one of the supported locks)::
+
+	/* dynamic */
+	seqcount_LOCKTYPE_t foo_seqcount;
+	seqcount_LOCKTYPE_init(&foo_seqcount, &lock);
+
+	/* static */
+	static seqcount_LOCKTYPE_t foo_seqcount =
+		SEQCNT_LOCKTYPE_ZERO(foo_seqcount, &lock);
+
+	/* C99 struct init */
+	struct {
+		.seq   = SEQCNT_LOCKTYPE_ZERO(foo.seq, &lock),
+	} foo;
+
+Write path: same as in :ref:`seqcount_t`, while running from a context
+with the associated LOCKTYPE lock acquired.
+
+Read path: same as in :ref:`seqcount_t`.
+
 .. _seqlock_t:
 
 Sequential locks (``seqlock_t``)

arch/ia64/include/asm/smp.h

@@ -18,7 +18,6 @@
 #include <linux/bitops.h>
 #include <linux/irqreturn.h>
 
-#include <asm/io.h>
 #include <asm/param.h>
 #include <asm/processor.h>
 #include <asm/ptrace.h>
@@ -44,11 +43,6 @@ ia64_get_lid (void)
 
 #ifdef CONFIG_SMP
 
-#define XTP_OFFSET		0x1e0008
-
-#define SMP_IRQ_REDIRECTION	(1 << 0)
-#define SMP_IPI_REDIRECTION	(1 << 1)
-
 #define raw_smp_processor_id() (current_thread_info()->cpu)
 
 extern struct smp_boot_data {
@@ -62,7 +56,6 @@ extern cpumask_t cpu_core_map[NR_CPUS];
 DECLARE_PER_CPU_SHARED_ALIGNED(cpumask_t, cpu_sibling_map);
 extern int smp_num_siblings;
 extern void __iomem *ipi_base_addr;
-extern unsigned char smp_int_redirect;
 
 extern volatile int ia64_cpu_to_sapicid[];
 #define cpu_physical_id(i)	ia64_cpu_to_sapicid[i]
@@ -84,34 +77,6 @@ cpu_logical_id (int cpuid)
 	return i;
 }
 
-/*
- * XTP control functions:
- *	min_xtp   : route all interrupts to this CPU
- *	normal_xtp: nominal XTP value
- *	max_xtp   : never deliver interrupts to this CPU.
- */
-
-static inline void
-min_xtp (void)
-{
-	if (smp_int_redirect & SMP_IRQ_REDIRECTION)
-		writeb(0x00, ipi_base_addr + XTP_OFFSET); /* XTP to min */
-}
-
-static inline void
-normal_xtp (void)
-{
-	if (smp_int_redirect & SMP_IRQ_REDIRECTION)
-		writeb(0x08, ipi_base_addr + XTP_OFFSET); /* XTP normal */
-}
-
-static inline void
-max_xtp (void)
-{
-	if (smp_int_redirect & SMP_IRQ_REDIRECTION)
-		writeb(0x0f, ipi_base_addr + XTP_OFFSET); /* Set XTP to max */
-}
-
 /* Upping and downing of CPUs */
 extern int __cpu_disable (void);
 extern void __cpu_die (unsigned int cpu);

arch/ia64/include/asm/xtp.h

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_IA64_XTP_H
+#define _ASM_IA64_XTP_H
+
+#include <asm/io.h>
+
+#ifdef CONFIG_SMP
+
+#define XTP_OFFSET		0x1e0008
+
+#define SMP_IRQ_REDIRECTION	(1 << 0)
+#define SMP_IPI_REDIRECTION	(1 << 1)
+
+extern unsigned char smp_int_redirect;
+
+/*
+ * XTP control functions:
+ *	min_xtp   : route all interrupts to this CPU
+ *	normal_xtp: nominal XTP value
+ *	max_xtp   : never deliver interrupts to this CPU.
+ */
+
+static inline void
+min_xtp (void)
+{
+	if (smp_int_redirect & SMP_IRQ_REDIRECTION)
+		writeb(0x00, ipi_base_addr + XTP_OFFSET); /* XTP to min */
+}
+
+static inline void
+normal_xtp (void)
+{
+	if (smp_int_redirect & SMP_IRQ_REDIRECTION)
+		writeb(0x08, ipi_base_addr + XTP_OFFSET); /* XTP normal */
+}
+
+static inline void
+max_xtp (void)
+{
+	if (smp_int_redirect & SMP_IRQ_REDIRECTION)
+		writeb(0x0f, ipi_base_addr + XTP_OFFSET); /* Set XTP to max */
+}
+
+#endif /* CONFIG_SMP */
+
+#endif /* _ASM_IA64_XTP_Hy */

arch/ia64/kernel/iosapic.c

@@ -95,6 +95,7 @@
 #include <asm/iosapic.h>
 #include <asm/processor.h>
 #include <asm/ptrace.h>
+#include <asm/xtp.h>
 
 #undef DEBUG_INTERRUPT_ROUTING
 

arch/ia64/kernel/irq.c

@@ -25,6 +25,7 @@
 #include <linux/kernel_stat.h>
 
 #include <asm/mca.h>
+#include <asm/xtp.h>
 
 /*
  * 'what should we do if we get a hw irq event on an illegal vector'.

arch/ia64/kernel/process.c

@@ -47,6 +47,7 @@
 #include <linux/uaccess.h>
 #include <asm/unwind.h>
 #include <asm/user.h>
+#include <asm/xtp.h>
 
 #include "entry.h"
 

arch/ia64/kernel/sal.c

@@ -18,6 +18,7 @@
 #include <asm/page.h>
 #include <asm/sal.h>
 #include <asm/pal.h>
+#include <asm/xtp.h>
 
  __cacheline_aligned DEFINE_SPINLOCK(sal_lock);
 unsigned long sal_platform_features;

arch/ia64/kernel/setup.c

@@ -65,6 +65,7 @@
 #include <asm/tlbflush.h>
 #include <asm/unistd.h>
 #include <asm/uv/uv.h>
+#include <asm/xtp.h>
 
 #if defined(CONFIG_SMP) && (IA64_CPU_SIZE > PAGE_SIZE)
 # error "struct cpuinfo_ia64 too big!"

arch/ia64/kernel/smp.c

@@ -45,6 +45,7 @@
 #include <asm/tlbflush.h>
 #include <asm/unistd.h>
 #include <asm/mca.h>
+#include <asm/xtp.h>
 
 /*
  * Note: alignment of 4 entries/cacheline was empirically determined

arch/parisc/include/asm/timex.h

@@ -7,6 +7,7 @@
 #ifndef _ASMPARISC_TIMEX_H
 #define _ASMPARISC_TIMEX_H
 
+#include <asm/special_insns.h>
 
 #define CLOCK_TICK_RATE	1193180 /* Underlying HZ */