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From 87c43f41a3330539e982f9e874704b04765ab4aa Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Fri, 11 Dec 2020 00:55:25 +0106
Subject: [PATCH 097/296] printk: track/limit recursion
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.35-rt39.tar.xz
Limit printk() recursion to 1 level. This is enough to print a
stacktrace for the printk call, should a WARN or BUG occur.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk.c | 74 ++++++++++++++++++++++++++++++++++++++++--
1 file changed, 71 insertions(+), 3 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f097f78b84e6..26b59e8fd2a0 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1941,6 +1941,65 @@ static void call_console_drivers(const char *ext_text, size_t ext_len,
}
}
+#ifdef CONFIG_PRINTK_NMI
+#define NUM_RECURSION_CTX 2
+#else
+#define NUM_RECURSION_CTX 1
+#endif
+
+struct printk_recursion {
+ char count[NUM_RECURSION_CTX];
+};
+
+static DEFINE_PER_CPU(struct printk_recursion, percpu_printk_recursion);
+static char printk_recursion_count[NUM_RECURSION_CTX];
+
+static char *printk_recursion_counter(void)
+{
+ struct printk_recursion *rec;
+ char *count;
+
+ if (!printk_percpu_data_ready()) {
+ count = &printk_recursion_count[0];
+ } else {
+ rec = this_cpu_ptr(&percpu_printk_recursion);
+
+ count = &rec->count[0];
+ }
+
+#ifdef CONFIG_PRINTK_NMI
+ if (in_nmi())
+ count++;
+#endif
+
+ return count;
+}
+
+static bool printk_enter_irqsave(unsigned long *flags)
+{
+ char *count;
+
+ local_irq_save(*flags);
+ count = printk_recursion_counter();
+ /* Only 1 level of recursion allowed. */
+ if (*count > 1) {
+ local_irq_restore(*flags);
+ return false;
+ }
+ (*count)++;
+
+ return true;
+}
+
+static void printk_exit_irqrestore(unsigned long flags)
+{
+ char *count;
+
+ count = printk_recursion_counter();
+ (*count)--;
+ local_irq_restore(flags);
+}
+
int printk_delay_msec __read_mostly;
static inline void printk_delay(void)
@@ -2041,11 +2100,13 @@ int vprintk_store(int facility, int level,
struct prb_reserved_entry e;
enum log_flags lflags = 0;
struct printk_record r;
+ unsigned long irqflags;
u16 trunc_msg_len = 0;
char prefix_buf[8];
u16 reserve_size;
va_list args2;
u16 text_len;
+ int ret = 0;
u64 ts_nsec;
/*
@@ -2056,6 +2117,9 @@ int vprintk_store(int facility, int level,
*/
ts_nsec = local_clock();
+ if (!printk_enter_irqsave(&irqflags))
+ return 0;
+
/*
* The sprintf needs to come first since the syslog prefix might be
* passed in as a parameter. An extra byte must be reserved so that
@@ -2093,7 +2157,8 @@ int vprintk_store(int facility, int level,
prb_commit(&e);
}
- return text_len;
+ ret = text_len;
+ goto out;
}
}
@@ -2109,7 +2174,7 @@ int vprintk_store(int facility, int level,
prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
if (!prb_reserve(&e, prb, &r))
- return 0;
+ goto out;
}
/* fill message */
@@ -2131,7 +2196,10 @@ int vprintk_store(int facility, int level,
else
prb_final_commit(&e);
- return (text_len + trunc_msg_len);
+ ret = text_len + trunc_msg_len;
+out:
+ printk_exit_irqrestore(irqflags);
+ return ret;
}
asmlinkage int vprintk_emit(int facility, int level,
--
2.30.2
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