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printk changes for 6.14

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Merge tag 'printk-for-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Prevent possible deadlocks, caused by the lock serializing per-CPU
   backtraces, by entering the deferred printk context

 - Enforce the right casting in LOG_BUF_LEN_MAX definition

* tag 'printk-for-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  printk: Defer legacy printing when holding printk_cpu_sync
  printk: Remove redundant deferred check in vprintk()
  printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX
This commit is contained in:
Linus Torvalds 2025-01-21 13:09:29 -08:00
commit 4ca6c02227
3 changed files with 18 additions and 11 deletions
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6
kernel/printk/internal.h
View file

@ -338,3 +338,9 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped);
void console_prepend_replay(struct printk_message *pmsg);
#endif
#ifdef CONFIG_SMP
bool is_printk_cpu_sync_owner(void);
#else
static inline bool is_printk_cpu_sync_owner(void) { return false; }
#endif

7
kernel/printk/printk.c
View file

@ -523,7 +523,7 @@ static struct latched_seq clear_seq = {
/* record buffer */
#define LOG_ALIGN __alignof__(unsigned long)
#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
#define LOG_BUF_LEN_MAX (u32)(1 << 31)
#define LOG_BUF_LEN_MAX ((u32)1 << 31)
static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
static char *log_buf = __log_buf;
static u32 log_buf_len = __LOG_BUF_LEN;
@ -4922,6 +4922,11 @@ void console_try_replay_all(void)
static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
bool is_printk_cpu_sync_owner(void)
{
return (atomic_read(&printk_cpu_sync_owner) == raw_smp_processor_id());
}
/**
* __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
* spinning lock is not owned by any CPU.

16
kernel/printk/printk_safe.c
View file

@ -61,10 +61,15 @@ bool is_printk_legacy_deferred(void)
/*
* The per-CPU variable @printk_context can be read safely in any
* context. CPU migration is always disabled when set.
*
* A context holding the printk_cpu_sync must not spin waiting for
* another CPU. For legacy printing, it could be the console_lock
* or the port lock.
*/
return (force_legacy_kthread() ||
this_cpu_read(printk_context) ||
in_nmi());
in_nmi() ||
is_printk_cpu_sync_owner());
}
asmlinkage int vprintk(const char *fmt, va_list args)
@ -74,15 +79,6 @@ asmlinkage int vprintk(const char *fmt, va_list args)
if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
#endif
/*
* Use the main logbuf even in NMI. But avoid calling console
* drivers that might have their own locks.
*/
if (is_printk_legacy_deferred())
return vprintk_deferred(fmt, args);
/* No obstacles. */
return vprintk_default(fmt, args);
}
EXPORT_SYMBOL(vprintk);