From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Alexander Potapenko <glider@google.com>,
Stephen Boyd <swboyd@chromium.org>,
Randy Dunlap <rdunlap@infradead.org>,
Nicholas Piggin <npiggin@gmail.com>
Subject: [PATCH printk v3 01/15] printk: rename cpulock functions
Date: Wed, 20 Apr 2022 01:52:23 +0206 [thread overview]
Message-ID: <20220419234637.357112-2-john.ogness@linutronix.de> (raw)
In-Reply-To: <20220419234637.357112-1-john.ogness@linutronix.de>
Since the printk cpulock is CPU-reentrant and since it is used
in all contexts, its usage must be carefully considered and
most likely will require programming locklessly. To avoid
mistaking the printk cpulock as a typical lock, rename it to
cpu_sync. The main functions then become:
printk_cpu_sync_get_irqsave(flags);
printk_cpu_sync_put_irqrestore(flags);
Add extra notes of caution in the function description to help
developers understand the requirements for correct usage.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
include/linux/printk.h | 54 +++++++++++++++++++-------------
kernel/printk/printk.c | 71 +++++++++++++++++++++---------------------
lib/dump_stack.c | 4 +--
lib/nmi_backtrace.c | 4 +--
4 files changed, 73 insertions(+), 60 deletions(-)
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 1522df223c0f..859323a52985 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -277,43 +277,55 @@ static inline void printk_trigger_flush(void)
#endif
#ifdef CONFIG_SMP
-extern int __printk_cpu_trylock(void);
-extern void __printk_wait_on_cpu_lock(void);
-extern void __printk_cpu_unlock(void);
+extern int __printk_cpu_sync_try_get(void);
+extern void __printk_cpu_sync_wait(void);
+extern void __printk_cpu_sync_put(void);
/**
- * printk_cpu_lock_irqsave() - Acquire the printk cpu-reentrant spinning
- * lock and disable interrupts.
+ * printk_cpu_sync_get_irqsave() - Acquire the printk cpu-reentrant spinning
+ * lock and disable interrupts.
* @flags: Stack-allocated storage for saving local interrupt state,
- * to be passed to printk_cpu_unlock_irqrestore().
+ * to be passed to printk_cpu_sync_put_irqrestore().
*
* If the lock is owned by another CPU, spin until it becomes available.
* Interrupts are restored while spinning.
+ *
+ * CAUTION: This function must be used carefully. It does not behave like a
+ * typical lock. Here are important things to watch out for...
+ *
+ * * This function is reentrant on the same CPU. Therefore the calling
+ * code must not assume exclusive access to data if code accessing the
+ * data can run reentrant or within NMI context on the same CPU.
+ *
+ * * If there exists usage of this function from NMI context, it becomes
+ * unsafe to perform any type of locking or spinning to wait for other
+ * CPUs after calling this function from any context. This includes
+ * using spinlocks or any other busy-waiting synchronization methods.
*/
-#define printk_cpu_lock_irqsave(flags) \
- for (;;) { \
- local_irq_save(flags); \
- if (__printk_cpu_trylock()) \
- break; \
- local_irq_restore(flags); \
- __printk_wait_on_cpu_lock(); \
+#define printk_cpu_sync_get_irqsave(flags) \
+ for (;;) { \
+ local_irq_save(flags); \
+ if (__printk_cpu_sync_try_get()) \
+ break; \
+ local_irq_restore(flags); \
+ __printk_cpu_sync_wait(); \
}
/**
- * printk_cpu_unlock_irqrestore() - Release the printk cpu-reentrant spinning
- * lock and restore interrupts.
- * @flags: Caller's saved interrupt state, from printk_cpu_lock_irqsave().
+ * printk_cpu_sync_put_irqrestore() - Release the printk cpu-reentrant spinning
+ * lock and restore interrupts.
+ * @flags: Caller's saved interrupt state, from printk_cpu_sync_get_irqsave().
*/
-#define printk_cpu_unlock_irqrestore(flags) \
+#define printk_cpu_sync_put_irqrestore(flags) \
do { \
- __printk_cpu_unlock(); \
+ __printk_cpu_sync_put(); \
local_irq_restore(flags); \
- } while (0) \
+ } while (0)
#else
-#define printk_cpu_lock_irqsave(flags) ((void)flags)
-#define printk_cpu_unlock_irqrestore(flags) ((void)flags)
+#define printk_cpu_sync_get_irqsave(flags) ((void)flags)
+#define printk_cpu_sync_put_irqrestore(flags) ((void)flags)
#endif /* CONFIG_SMP */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index da03c15ecc89..13a1eebe72af 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3667,26 +3667,26 @@ EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
#endif
#ifdef CONFIG_SMP
-static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1);
-static atomic_t printk_cpulock_nested = ATOMIC_INIT(0);
+static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
+static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
/**
- * __printk_wait_on_cpu_lock() - Busy wait until the printk cpu-reentrant
- * spinning lock is not owned by any CPU.
+ * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
+ * spinning lock is not owned by any CPU.
*
* Context: Any context.
*/
-void __printk_wait_on_cpu_lock(void)
+void __printk_cpu_sync_wait(void)
{
do {
cpu_relax();
- } while (atomic_read(&printk_cpulock_owner) != -1);
+ } while (atomic_read(&printk_cpu_sync_owner) != -1);
}
-EXPORT_SYMBOL(__printk_wait_on_cpu_lock);
+EXPORT_SYMBOL(__printk_cpu_sync_wait);
/**
- * __printk_cpu_trylock() - Try to acquire the printk cpu-reentrant
- * spinning lock.
+ * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
+ * spinning lock.
*
* If no processor has the lock, the calling processor takes the lock and
* becomes the owner. If the calling processor is already the owner of the
@@ -3695,7 +3695,7 @@ EXPORT_SYMBOL(__printk_wait_on_cpu_lock);
* Context: Any context. Expects interrupts to be disabled.
* Return: 1 on success, otherwise 0.
*/
-int __printk_cpu_trylock(void)
+int __printk_cpu_sync_try_get(void)
{
int cpu;
int old;
@@ -3705,79 +3705,80 @@ int __printk_cpu_trylock(void)
/*
* Guarantee loads and stores from this CPU when it is the lock owner
* are _not_ visible to the previous lock owner. This pairs with
- * __printk_cpu_unlock:B.
+ * __printk_cpu_sync_put:B.
*
* Memory barrier involvement:
*
- * If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B, then
- * __printk_cpu_unlock:A can never read from __printk_cpu_trylock:B.
+ * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
+ * then __printk_cpu_sync_put:A can never read from
+ * __printk_cpu_sync_try_get:B.
*
* Relies on:
*
- * RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
+ * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
* of the previous CPU
* matching
- * ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
- * of this CPU
+ * ACQUIRE from __printk_cpu_sync_try_get:A to
+ * __printk_cpu_sync_try_get:B of this CPU
*/
- old = atomic_cmpxchg_acquire(&printk_cpulock_owner, -1,
- cpu); /* LMM(__printk_cpu_trylock:A) */
+ old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
+ cpu); /* LMM(__printk_cpu_sync_try_get:A) */
if (old == -1) {
/*
* This CPU is now the owner and begins loading/storing
- * data: LMM(__printk_cpu_trylock:B)
+ * data: LMM(__printk_cpu_sync_try_get:B)
*/
return 1;
} else if (old == cpu) {
/* This CPU is already the owner. */
- atomic_inc(&printk_cpulock_nested);
+ atomic_inc(&printk_cpu_sync_nested);
return 1;
}
return 0;
}
-EXPORT_SYMBOL(__printk_cpu_trylock);
+EXPORT_SYMBOL(__printk_cpu_sync_try_get);
/**
- * __printk_cpu_unlock() - Release the printk cpu-reentrant spinning lock.
+ * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
*
* The calling processor must be the owner of the lock.
*
* Context: Any context. Expects interrupts to be disabled.
*/
-void __printk_cpu_unlock(void)
+void __printk_cpu_sync_put(void)
{
- if (atomic_read(&printk_cpulock_nested)) {
- atomic_dec(&printk_cpulock_nested);
+ if (atomic_read(&printk_cpu_sync_nested)) {
+ atomic_dec(&printk_cpu_sync_nested);
return;
}
/*
* This CPU is finished loading/storing data:
- * LMM(__printk_cpu_unlock:A)
+ * LMM(__printk_cpu_sync_put:A)
*/
/*
* Guarantee loads and stores from this CPU when it was the
* lock owner are visible to the next lock owner. This pairs
- * with __printk_cpu_trylock:A.
+ * with __printk_cpu_sync_try_get:A.
*
* Memory barrier involvement:
*
- * If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B,
- * then __printk_cpu_trylock:B reads from __printk_cpu_unlock:A.
+ * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
+ * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
*
* Relies on:
*
- * RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
+ * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
* of this CPU
* matching
- * ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
- * of the next CPU
+ * ACQUIRE from __printk_cpu_sync_try_get:A to
+ * __printk_cpu_sync_try_get:B of the next CPU
*/
- atomic_set_release(&printk_cpulock_owner,
- -1); /* LMM(__printk_cpu_unlock:B) */
+ atomic_set_release(&printk_cpu_sync_owner,
+ -1); /* LMM(__printk_cpu_sync_put:B) */
}
-EXPORT_SYMBOL(__printk_cpu_unlock);
+EXPORT_SYMBOL(__printk_cpu_sync_put);
#endif /* CONFIG_SMP */
diff --git a/lib/dump_stack.c b/lib/dump_stack.c
index 6b7f1bf6715d..83471e81501a 100644
--- a/lib/dump_stack.c
+++ b/lib/dump_stack.c
@@ -102,9 +102,9 @@ asmlinkage __visible void dump_stack_lvl(const char *log_lvl)
* Permit this cpu to perform nested stack dumps while serialising
* against other CPUs
*/
- printk_cpu_lock_irqsave(flags);
+ printk_cpu_sync_get_irqsave(flags);
__dump_stack(log_lvl);
- printk_cpu_unlock_irqrestore(flags);
+ printk_cpu_sync_put_irqrestore(flags);
}
EXPORT_SYMBOL(dump_stack_lvl);
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index 199ab201d501..d01aec6ae15c 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -99,7 +99,7 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
* Allow nested NMI backtraces while serializing
* against other CPUs.
*/
- printk_cpu_lock_irqsave(flags);
+ printk_cpu_sync_get_irqsave(flags);
if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
cpu, (void *)instruction_pointer(regs));
@@ -110,7 +110,7 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
else
dump_stack();
}
- printk_cpu_unlock_irqrestore(flags);
+ printk_cpu_sync_put_irqrestore(flags);
cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
return true;
}
--
2.30.2
next prev parent reply other threads:[~2022-04-19 23:47 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-19 23:46 [PATCH printk v3 00/15] printk/for-next John Ogness
2022-04-19 23:46 ` John Ogness [this message]
2022-04-19 23:46 ` [PATCH printk v3 02/15] printk: cpu sync always disable interrupts John Ogness
2022-04-19 23:46 ` [PATCH printk v3 03/15] printk: add missing memory barrier to wake_up_klogd() John Ogness
2022-04-20 12:34 ` Petr Mladek
2022-04-19 23:46 ` [PATCH printk v3 04/15] printk: wake up all waiters John Ogness
2022-04-20 12:36 ` Petr Mladek
2022-04-19 23:46 ` [PATCH printk v3 05/15] printk: wake waiters for safe and NMI contexts John Ogness
2022-04-20 13:55 ` Petr Mladek
2022-04-19 23:46 ` [PATCH printk v3 06/15] printk: get caller_id/timestamp after migration disable John Ogness
2022-04-19 23:46 ` [PATCH printk v3 07/15] printk: call boot_delay_msec() in printk_delay() John Ogness
2022-04-19 23:46 ` [PATCH printk v3 08/15] printk: add con_printk() macro for console details John Ogness
2022-04-20 14:01 ` Petr Mladek
2022-04-19 23:46 ` [PATCH printk v3 09/15] printk: refactor and rework printing logic John Ogness
2022-04-20 14:55 ` Petr Mladek
2022-04-19 23:46 ` [PATCH printk v3 10/15] printk: move buffer definitions into console_emit_next_record() caller John Ogness
2022-04-19 23:46 ` [PATCH printk v3 11/15] printk: add pr_flush() John Ogness
2022-04-20 15:10 ` Petr Mladek
2022-04-19 23:46 ` [PATCH printk v3 12/15] printk: add functions to prefer direct printing John Ogness
2022-04-19 23:46 ` [PATCH printk v3 13/15] printk: add kthread console printers John Ogness
2022-04-20 17:53 ` Petr Mladek
2022-04-20 20:02 ` John Ogness
2022-04-21 14:25 ` Petr Mladek
2022-04-19 23:46 ` [PATCH printk v3 14/15] printk: extend console_lock for proper kthread support John Ogness
2022-04-20 2:13 ` kernel test robot
2022-04-20 13:32 ` John Ogness
2022-04-20 4:04 ` kernel test robot
2022-04-21 12:41 ` Petr Mladek
2022-04-21 14:30 ` John Ogness
2022-04-22 13:03 ` Petr Mladek
2022-04-22 14:14 ` John Ogness
2022-04-22 15:15 ` Petr Mladek
2022-04-22 21:25 ` John Ogness
2022-04-25 15:18 ` Petr Mladek
2022-04-25 19:10 ` John Ogness
2022-04-19 23:46 ` [PATCH printk v3 15/15] printk: remove @console_locked John Ogness
2022-04-21 12:46 ` Petr Mladek
2022-04-21 14:40 ` [PATCH printk v3 00/15] printk/for-next Petr Mladek
2022-04-21 15:02 ` John Ogness
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