From 61598093bbdd283a7edc367d900f223070ead8d2 Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Fri, 10 May 2024 07:43:03 +0000
Subject: [PATCH] add ax88772C AX88772C_eeprom_tools
---
kernel/kernel/printk/printk_safe.c | 422 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 422 insertions(+), 0 deletions(-)
diff --git a/kernel/kernel/printk/printk_safe.c b/kernel/kernel/printk/printk_safe.c
new file mode 100644
index 0000000..2e9e3ed
--- /dev/null
+++ b/kernel/kernel/printk/printk_safe.c
@@ -0,0 +1,422 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * printk_safe.c - Safe printk for printk-deadlock-prone contexts
+ */
+
+#include <linux/preempt.h>
+#include <linux/spinlock.h>
+#include <linux/debug_locks.h>
+#include <linux/kdb.h>
+#include <linux/smp.h>
+#include <linux/cpumask.h>
+#include <linux/irq_work.h>
+#include <linux/printk.h>
+#include <linux/kprobes.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 examining 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.
+ */
+
+#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);
+
+static DEFINE_RAW_SPINLOCK(safe_read_lock);
+
+#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_percpu_data_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)
+{
+ 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(&safe_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(&safe_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);
+ }
+
+ if (raw_spin_is_locked(&safe_read_lock)) {
+ if (num_online_cpus() > 1)
+ return;
+
+ debug_locks_off();
+ raw_spin_lock_init(&safe_read_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 noinstr printk_nmi_enter(void)
+{
+ this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
+}
+
+void noinstr printk_nmi_exit(void)
+{
+ this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
+}
+
+/*
+ * 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)
+{
+#ifdef CONFIG_KGDB_KDB
+ /* Allow to pass printk() to kdb but avoid a recursion. */
+ if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
+ return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
+#endif
+
+ /*
+ * 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, 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
+ }
+
+ /* Flush pending messages that did not have scheduled IRQ works. */
+ printk_safe_flush();
+}
--
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