From fbd1b769b3f7f77b4de8c2e0145a64c2d158c3cb Mon Sep 17 00:00:00 2001 From: John Ogness Date: Fri, 11 Dec 2020 00:55:25 +0106 Subject: [PATCH 096/323] printk: track/limit recursion Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.215-rt107.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 Signed-off-by: Sebastian Andrzej Siewior --- 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 1e7ab017be193..08a49c8e7239e 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1949,6 +1949,65 @@ 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) @@ -2049,11 +2108,13 @@ 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; /* @@ -2064,6 +2125,9 @@ 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 @@ -2101,7 +2165,8 @@ int vprintk_store(int facility, int level, prb_commit(&e); } - return text_len; + ret = text_len; + goto out; } } @@ -2117,7 +2182,7 @@ 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 */ @@ -2139,7 +2204,10 @@ 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, -- 2.44.0