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Subject[RFC PATCH v1 11/25] printk_safe: remove printk safe code
Date
vprintk variants are now NMI-safe so there is no longer a need for
the "safe" calls.

NOTE: This also removes printk flushing functionality.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
include/linux/hardirq.h | 2 -
include/linux/printk.h | 27 ---
init/main.c | 1 -
kernel/kexec_core.c | 1 -
kernel/panic.c | 3 -
kernel/printk/Makefile | 1 -
kernel/printk/internal.h | 30 +---
kernel/printk/printk.c | 13 +-
kernel/printk/printk_safe.c | 427 --------------------------------------------
kernel/trace/trace.c | 2 -
lib/nmi_backtrace.c | 6 -
11 files changed, 7 insertions(+), 506 deletions(-)
delete mode 100644 kernel/printk/printk_safe.c

diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 0fbbcdf0c178..c1effa24a71d 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -62,7 +62,6 @@ extern void irq_exit(void);

#define nmi_enter() \
do { \
- printk_nmi_enter(); \
lockdep_off(); \
ftrace_nmi_enter(); \
BUG_ON(in_nmi()); \
@@ -79,7 +78,6 @@ extern void irq_exit(void);
preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \
ftrace_nmi_exit(); \
lockdep_on(); \
- printk_nmi_exit(); \
} while (0)

#endif /* LINUX_HARDIRQ_H */
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 77740a506ebb..a79a736b54b6 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -145,18 +145,6 @@ static inline __printf(1, 2) __cold
void early_printk(const char *s, ...) { }
#endif

-#ifdef CONFIG_PRINTK_NMI
-extern void printk_nmi_enter(void);
-extern void printk_nmi_exit(void);
-extern void printk_nmi_direct_enter(void);
-extern void printk_nmi_direct_exit(void);
-#else
-static inline void printk_nmi_enter(void) { }
-static inline void printk_nmi_exit(void) { }
-static inline void printk_nmi_direct_enter(void) { }
-static inline void printk_nmi_direct_exit(void) { }
-#endif /* PRINTK_NMI */
-
#ifdef CONFIG_PRINTK
asmlinkage __printf(5, 0)
int vprintk_emit(int facility, int level,
@@ -201,9 +189,6 @@ __printf(1, 2) void dump_stack_set_arch_desc(const char *fmt, ...);
void dump_stack_print_info(const char *log_lvl);
void show_regs_print_info(const char *log_lvl);
extern asmlinkage void dump_stack(void) __cold;
-extern void printk_safe_init(void);
-extern void printk_safe_flush(void);
-extern void printk_safe_flush_on_panic(void);
#else
static inline __printf(1, 0)
int vprintk(const char *s, va_list args)
@@ -267,18 +252,6 @@ static inline void show_regs_print_info(const char *log_lvl)
static inline void dump_stack(void)
{
}
-
-static inline void printk_safe_init(void)
-{
-}
-
-static inline void printk_safe_flush(void)
-{
-}
-
-static inline void printk_safe_flush_on_panic(void)
-{
-}
#endif

extern int kptr_restrict;
diff --git a/init/main.c b/init/main.c
index e2e80ca3165a..aec02435f00b 100644
--- a/init/main.c
+++ b/init/main.c
@@ -648,7 +648,6 @@ asmlinkage __visible void __init start_kernel(void)
softirq_init();
timekeeping_init();
time_init();
- printk_safe_init();
perf_event_init();
profile_init();
call_function_init();
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index d7140447be75..bbe21da47e2e 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -972,7 +972,6 @@ void crash_kexec(struct pt_regs *regs)
old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
if (old_cpu == PANIC_CPU_INVALID) {
/* This is the 1st CPU which comes here, so go ahead. */
- printk_safe_flush_on_panic();
__crash_kexec(regs);

/*
diff --git a/kernel/panic.c b/kernel/panic.c
index f121e6ba7e11..09a836b3c687 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -223,7 +223,6 @@ void panic(const char *fmt, ...)
* Bypass the panic_cpu check and call __crash_kexec directly.
*/
if (!_crash_kexec_post_notifiers) {
- printk_safe_flush_on_panic();
__crash_kexec(NULL);

/*
@@ -247,8 +246,6 @@ void panic(const char *fmt, ...)
*/
atomic_notifier_call_chain(&panic_notifier_list, 0, buf);

- /* Call flush even twice. It tries harder with a single online CPU */
- printk_safe_flush_on_panic();
kmsg_dump(KMSG_DUMP_PANIC);

/*
diff --git a/kernel/printk/Makefile b/kernel/printk/Makefile
index 4a2ffc39eb95..85405bdcf2b3 100644
--- a/kernel/printk/Makefile
+++ b/kernel/printk/Makefile
@@ -1,3 +1,2 @@
obj-y = printk.o
-obj-$(CONFIG_PRINTK) += printk_safe.o
obj-$(CONFIG_A11Y_BRAILLE_CONSOLE) += braille.o
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 0f1898820cba..59ad43dba837 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -32,32 +32,6 @@ int vprintk_store(int facility, int level,
__printf(1, 0) int vprintk_default(const char *fmt, va_list args);
__printf(1, 0) int vprintk_deferred(const char *fmt, va_list args);
__printf(1, 0) int vprintk_func(const char *fmt, va_list args);
-void __printk_safe_enter(void);
-void __printk_safe_exit(void);
-
-#define printk_safe_enter_irqsave(flags) \
- do { \
- local_irq_save(flags); \
- __printk_safe_enter(); \
- } while (0)
-
-#define printk_safe_exit_irqrestore(flags) \
- do { \
- __printk_safe_exit(); \
- local_irq_restore(flags); \
- } while (0)
-
-#define printk_safe_enter_irq() \
- do { \
- local_irq_disable(); \
- __printk_safe_enter(); \
- } while (0)
-
-#define printk_safe_exit_irq() \
- do { \
- __printk_safe_exit(); \
- local_irq_enable(); \
- } while (0)

void defer_console_output(void);

@@ -70,10 +44,10 @@ __printf(1, 0) int vprintk_func(const char *fmt, va_list args) { return 0; }
* semaphore and some of console functions (console_unlock()/etc.), so
* printk-safe must preserve the existing local IRQ guarantees.
*/
+#endif /* CONFIG_PRINTK */
+
#define printk_safe_enter_irqsave(flags) local_irq_save(flags)
#define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)

#define printk_safe_enter_irq() local_irq_disable()
#define printk_safe_exit_irq() local_irq_enable()
-
-#endif /* CONFIG_PRINTK */
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index b6a6f1002741..073ff9fd6872 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1675,13 +1675,6 @@ static bool cont_add(int facility, int level, enum log_flags flags, const char *
}
#endif /* 0 */

-int vprintk_store(int facility, int level,
- const char *dict, size_t dictlen,
- const char *fmt, va_list args)
-{
- return vprintk_emit(facility, level, dict, dictlen, fmt, args);
-}
-
/* ring buffer used as memory allocator for temporary sprint buffers */
DECLARE_STATIC_PRINTKRB(sprint_rb,
ilog2(PRINTK_RECORD_MAX + sizeof(struct prb_entry) +
@@ -1752,6 +1745,11 @@ asmlinkage int vprintk_emit(int facility, int level,
}
EXPORT_SYMBOL(vprintk_emit);

+__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
+{
+ return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
+}
+
asmlinkage int vprintk(const char *fmt, va_list args)
{
return vprintk_func(fmt, args);
@@ -3142,5 +3140,4 @@ void kmsg_dump_rewind(struct kmsg_dumper *dumper)
logbuf_unlock_irqrestore(flags);
}
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
-
#endif
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
deleted file mode 100644
index 0913b4d385de..000000000000
--- a/kernel/printk/printk_safe.c
+++ /dev/null
@@ -1,427 +0,0 @@
-/*
- * printk_safe.c - Safe printk for printk-deadlock-prone contexts
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version 2
- * of the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, see <http://www.gnu.org/licenses/>.
- */
-
-#include <linux/preempt.h>
-#include <linux/spinlock.h>
-#include <linux/debug_locks.h>
-#include <linux/smp.h>
-#include <linux/cpumask.h>
-#include <linux/irq_work.h>
-#include <linux/printk.h>
-
-#include "internal.h"
-
-/*
- * printk() could not take logbuf_lock in NMI context. Instead,
- * it uses an alternative implementation that temporary stores
- * the strings into a per-CPU buffer. The content of the buffer
- * is later flushed into the main ring buffer via IRQ work.
- *
- * The alternative implementation is chosen transparently
- * by examinig current printk() context mask stored in @printk_context
- * per-CPU variable.
- *
- * The implementation allows to flush the strings also from another CPU.
- * There are situations when we want to make sure that all buffers
- * were handled or when IRQs are blocked.
- */
-static int printk_safe_irq_ready __read_mostly;
-
-#define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) - \
- sizeof(atomic_t) - \
- sizeof(atomic_t) - \
- sizeof(struct irq_work))
-
-struct printk_safe_seq_buf {
- atomic_t len; /* length of written data */
- atomic_t message_lost;
- struct irq_work work; /* IRQ work that flushes the buffer */
- unsigned char buffer[SAFE_LOG_BUF_LEN];
-};
-
-static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
-static DEFINE_PER_CPU(int, printk_context);
-
-#ifdef CONFIG_PRINTK_NMI
-static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
-#endif
-
-/* Get flushed in a more safe context. */
-static void queue_flush_work(struct printk_safe_seq_buf *s)
-{
- if (printk_safe_irq_ready)
- irq_work_queue(&s->work);
-}
-
-/*
- * Add a message to per-CPU context-dependent buffer. NMI and printk-safe
- * have dedicated buffers, because otherwise printk-safe preempted by
- * NMI-printk would have overwritten the NMI messages.
- *
- * The messages are flushed from irq work (or from panic()), possibly,
- * from other CPU, concurrently with printk_safe_log_store(). Should this
- * happen, printk_safe_log_store() will notice the buffer->len mismatch
- * and repeat the write.
- */
-static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
- const char *fmt, va_list args)
-{
- int add;
- size_t len;
- va_list ap;
-
-again:
- len = atomic_read(&s->len);
-
- /* The trailing '\0' is not counted into len. */
- if (len >= sizeof(s->buffer) - 1) {
- atomic_inc(&s->message_lost);
- queue_flush_work(s);
- return 0;
- }
-
- /*
- * Make sure that all old data have been read before the buffer
- * was reset. This is not needed when we just append data.
- */
- if (!len)
- smp_rmb();
-
- va_copy(ap, args);
- add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
- va_end(ap);
- if (!add)
- return 0;
-
- /*
- * Do it once again if the buffer has been flushed in the meantime.
- * Note that atomic_cmpxchg() is an implicit memory barrier that
- * makes sure that the data were written before updating s->len.
- */
- if (atomic_cmpxchg(&s->len, len, len + add) != len)
- goto again;
-
- queue_flush_work(s);
- return add;
-}
-
-static inline void printk_safe_flush_line(const char *text, int len)
-{
- /*
- * Avoid any console drivers calls from here, because we may be
- * in NMI or printk_safe context (when in panic). The messages
- * must go only into the ring buffer at this stage. Consoles will
- * get explicitly called later when a crashdump is not generated.
- */
- printk_deferred("%.*s", len, text);
-}
-
-/* printk part of the temporary buffer line by line */
-static int printk_safe_flush_buffer(const char *start, size_t len)
-{
- const char *c, *end;
- bool header;
-
- c = start;
- end = start + len;
- header = true;
-
- /* Print line by line. */
- while (c < end) {
- if (*c == '\n') {
- printk_safe_flush_line(start, c - start + 1);
- start = ++c;
- header = true;
- continue;
- }
-
- /* Handle continuous lines or missing new line. */
- if ((c + 1 < end) && printk_get_level(c)) {
- if (header) {
- c = printk_skip_level(c);
- continue;
- }
-
- printk_safe_flush_line(start, c - start);
- start = c++;
- header = true;
- continue;
- }
-
- header = false;
- c++;
- }
-
- /* Check if there was a partial line. Ignore pure header. */
- if (start < end && !header) {
- static const char newline[] = KERN_CONT "\n";
-
- printk_safe_flush_line(start, end - start);
- printk_safe_flush_line(newline, strlen(newline));
- }
-
- return len;
-}
-
-static void report_message_lost(struct printk_safe_seq_buf *s)
-{
- int lost = atomic_xchg(&s->message_lost, 0);
-
- if (lost)
- printk_deferred("Lost %d message(s)!\n", lost);
-}
-
-/*
- * Flush data from the associated per-CPU buffer. The function
- * can be called either via IRQ work or independently.
- */
-static void __printk_safe_flush(struct irq_work *work)
-{
- static raw_spinlock_t read_lock =
- __RAW_SPIN_LOCK_INITIALIZER(read_lock);
- struct printk_safe_seq_buf *s =
- container_of(work, struct printk_safe_seq_buf, work);
- unsigned long flags;
- size_t len;
- int i;
-
- /*
- * The lock has two functions. First, one reader has to flush all
- * available message to make the lockless synchronization with
- * writers easier. Second, we do not want to mix messages from
- * different CPUs. This is especially important when printing
- * a backtrace.
- */
- raw_spin_lock_irqsave(&read_lock, flags);
-
- i = 0;
-more:
- len = atomic_read(&s->len);
-
- /*
- * This is just a paranoid check that nobody has manipulated
- * the buffer an unexpected way. If we printed something then
- * @len must only increase. Also it should never overflow the
- * buffer size.
- */
- if ((i && i >= len) || len > sizeof(s->buffer)) {
- const char *msg = "printk_safe_flush: internal error\n";
-
- printk_safe_flush_line(msg, strlen(msg));
- len = 0;
- }
-
- if (!len)
- goto out; /* Someone else has already flushed the buffer. */
-
- /* Make sure that data has been written up to the @len */
- smp_rmb();
- i += printk_safe_flush_buffer(s->buffer + i, len - i);
-
- /*
- * Check that nothing has got added in the meantime and truncate
- * the buffer. Note that atomic_cmpxchg() is an implicit memory
- * barrier that makes sure that the data were copied before
- * updating s->len.
- */
- if (atomic_cmpxchg(&s->len, len, 0) != len)
- goto more;
-
-out:
- report_message_lost(s);
- raw_spin_unlock_irqrestore(&read_lock, flags);
-}
-
-/**
- * printk_safe_flush - flush all per-cpu nmi buffers.
- *
- * The buffers are flushed automatically via IRQ work. This function
- * is useful only when someone wants to be sure that all buffers have
- * been flushed at some point.
- */
-void printk_safe_flush(void)
-{
- int cpu;
-
- for_each_possible_cpu(cpu) {
-#ifdef CONFIG_PRINTK_NMI
- __printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);
-#endif
- __printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);
- }
-}
-
-/**
- * printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system
- * goes down.
- *
- * Similar to printk_safe_flush() but it can be called even in NMI context when
- * the system goes down. It does the best effort to get NMI messages into
- * the main ring buffer.
- *
- * Note that it could try harder when there is only one CPU online.
- */
-void printk_safe_flush_on_panic(void)
-{
- /*
- * Make sure that we could access the main ring buffer.
- * Do not risk a double release when more CPUs are up.
- */
- if (raw_spin_is_locked(&logbuf_lock)) {
- if (num_online_cpus() > 1)
- return;
-
- debug_locks_off();
- raw_spin_lock_init(&logbuf_lock);
- }
-
- printk_safe_flush();
-}
-
-#ifdef CONFIG_PRINTK_NMI
-/*
- * Safe printk() for NMI context. It uses a per-CPU buffer to
- * store the message. NMIs are not nested, so there is always only
- * one writer running. But the buffer might get flushed from another
- * CPU, so we need to be careful.
- */
-static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
-{
- struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
-
- return printk_safe_log_store(s, fmt, args);
-}
-
-void notrace printk_nmi_enter(void)
-{
- this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
-}
-
-void notrace printk_nmi_exit(void)
-{
- this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
-}
-
-/*
- * Marks a code that might produce many messages in NMI context
- * and the risk of losing them is more critical than eventual
- * reordering.
- *
- * It has effect only when called in NMI context. Then printk()
- * will try to store the messages into the main logbuf directly
- * and use the per-CPU buffers only as a fallback when the lock
- * is not available.
- */
-void printk_nmi_direct_enter(void)
-{
- if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
- this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
-}
-
-void printk_nmi_direct_exit(void)
-{
- this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK);
-}
-
-#else
-
-static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
-{
- return 0;
-}
-
-#endif /* CONFIG_PRINTK_NMI */
-
-/*
- * Lock-less printk(), to avoid deadlocks should the printk() recurse
- * into itself. It uses a per-CPU buffer to store the message, just like
- * NMI.
- */
-static __printf(1, 0) int vprintk_safe(const char *fmt, va_list args)
-{
- struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
-
- return printk_safe_log_store(s, fmt, args);
-}
-
-/* Can be preempted by NMI. */
-void __printk_safe_enter(void)
-{
- this_cpu_inc(printk_context);
-}
-
-/* Can be preempted by NMI. */
-void __printk_safe_exit(void)
-{
- this_cpu_dec(printk_context);
-}
-
-__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
-{
- /*
- * Try to use the main logbuf even in NMI. But avoid calling console
- * drivers that might have their own locks.
- */
- if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
- raw_spin_trylock(&logbuf_lock)) {
- int len;
-
- len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, 0, fmt, args);
- raw_spin_unlock(&logbuf_lock);
- defer_console_output();
- return len;
- }
-
- /* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
- if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
- return vprintk_nmi(fmt, args);
-
- /* Use extra buffer to prevent a recursion deadlock in safe mode. */
- if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
- return vprintk_safe(fmt, args);
-
- /* No obstacles. */
- return vprintk_default(fmt, args);
-}
-
-void __init printk_safe_init(void)
-{
- int cpu;
-
- for_each_possible_cpu(cpu) {
- struct printk_safe_seq_buf *s;
-
- s = &per_cpu(safe_print_seq, cpu);
- init_irq_work(&s->work, __printk_safe_flush);
-
-#ifdef CONFIG_PRINTK_NMI
- s = &per_cpu(nmi_print_seq, cpu);
- init_irq_work(&s->work, __printk_safe_flush);
-#endif
- }
-
- /*
- * In the highly unlikely event that a NMI were to trigger at
- * this moment. Make sure IRQ work is set up before this
- * variable is set.
- */
- barrier();
- printk_safe_irq_ready = 1;
-
- /* Flush pending messages that did not have scheduled IRQ works. */
- printk_safe_flush();
-}
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c521b7347482..cfce391621c0 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8363,7 +8363,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
tracing_off();

local_irq_save(flags);
- printk_nmi_direct_enter();

/* Simulate the iterator */
trace_init_global_iter(&iter);
@@ -8444,7 +8443,6 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)
atomic_dec(&per_cpu_ptr(iter.trace_buffer->data, cpu)->disabled);
}
atomic_dec(&dump_running);
- printk_nmi_direct_exit();
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(ftrace_dump);
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index 15ca78e1c7d4..77bf84987cda 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -75,12 +75,6 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
touch_softlockup_watchdog();
}

- /*
- * Force flush any remote buffers that might be stuck in IRQ context
- * and therefore could not run their irq_work.
- */
- printk_safe_flush();
-
clear_bit_unlock(0, &backtrace_flag);
put_cpu();
}
--
2.11.0
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