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printk: Avoid false positive lockdep report for legacy printing

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BugLink: https://bugs.launchpad.net/bugs/2060704

Legacy console printing from printk() caller context may invoke
the console driver from atomic context. This leads to a lockdep
splat because the console driver will acquire a sleeping lock
and the caller may already hold a spinning lock. This is noticed
by lockdep on !PREEMPT_RT configurations because it will lead to
a problem on PREEMPT_RT.

However, on PREEMPT_RT the printing path from atomic context is
always avoided and the console driver is always invoked from a
dedicated thread. Thus the lockdep splat on !PREEMPT_RT is a
false positive.

For !PREEMPT_RT override the lock-context before invoking the
console driver to avoid the false positive.

Do not override the lock-context for PREEMPT_RT in order to
allow lockdep to catch any real locking context issues related
to the write callback usage.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kevin Becker <kevin.becker@canonical.com>
This commit is contained in:
John Ogness
2023-12-11 09:34:16 +00:00
committed by Kevin Becker
parent cdd67ae59b
commit 26331faec8
1 changed files with 30 additions and 1 deletions
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kernel/printk/printk.c
+30 -1
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@@ -2990,6 +2990,33 @@ out:
return true;
}
/*
* Legacy console printing from printk() caller context does not respect
* raw_spinlock/spinlock nesting. For !PREEMPT_RT the lockdep warning is a
* false positive. For PREEMPT_RT the false positive condition does not
* occur.
*
* This map is used to establish LD_WAIT_SLEEP context for the console write
* callbacks when legacy printing to avoid false positive lockdep complaints,
* thus allowing lockdep to continue to function for real issues.
*/
#ifdef CONFIG_PREEMPT_RT
static inline void printk_legacy_lock_map_acquire_try(void) { }
static inline void printk_legacy_lock_map_release(void) { }
#else
static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP);
static inline void printk_legacy_lock_map_acquire_try(void)
{
lock_map_acquire_try(&printk_legacy_map);
}
static inline void printk_legacy_lock_map_release(void)
{
lock_map_release(&printk_legacy_map);
}
#endif /* CONFIG_PREEMPT_RT */
/*
* Used as the printk buffers for non-panic, serialized console printing.
* This is for legacy (!CON_NBCON) as well as all boot (CON_BOOT) consoles.
@@ -3045,7 +3072,7 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co
/*
* With forced threading this function is either in a thread
* or panic context. So there is no need for concern about
* printk reentrance or handovers.
* printk reentrance, handovers, or lockdep complaints.
*/
con->write(con, outbuf, pmsg.outbuf_len);
@@ -3067,7 +3094,9 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co
/* Do not trace print latency. */
stop_critical_timings();
printk_legacy_lock_map_acquire_try();
con->write(con, outbuf, pmsg.outbuf_len);
printk_legacy_lock_map_release();
start_critical_timings();