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staging: fbtft: make dirty_lock IRQ-safe

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fbtft_mkdirty() can be reached from the fbcon rendering path while
processing printk() in hardirq context. Meanwhile, dirty_lock is also
taken by fbtft_deferred_io() in workqueue context with local interrupts
enabled.

Lockdep reports a possible IRQ lock inversion involving dirty_lock and
console_owner. A hardirq can interrupt a CPU holding dirty_lock and
enter the console rendering path, which can attempt to acquire
dirty_lock again.

The following lockdep report was observed on an RK3566 system with
CONFIG_PROVE_LOCKING enabled:

  WARNING: possible irq lock inversion dependency detected
  swapper/2/0 just changed the state of lock:
  (console_owner){-...}-{0:0}
  but this lock took another, HARDIRQ-unsafe lock in the past:
  (&par->dirty_lock){+.+.}-{2:2}

  CPU0                    CPU1
  ----                    ----
  lock(&par->dirty_lock);
                         local_irq_disable();
                         lock(console_owner);
                         lock(&par->dirty_lock);
  <Interrupt>
    lock(console_owner);

  *** DEADLOCK ***

Use spin_lock_irqsave() for fbtft_mkdirty() and spin_lock_irq() for
fbtft_deferred_io(). They only access the dirty line range, so the
IRQ-off regions remain short.

Fixes: c296d5f995 ("staging: fbtft: core support")
Signed-off-by: Hui Su <sh_def@163.com>
Link: https://lore.kernel.org/lkml/20260804173712.176017-1-sh_def@163.com/
Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://patch.msgid.link/20260807150953.2811933-3-sh_def@163.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Hui Su 2026-08-07 23:09:55 +08:00 • committed by Greg Kroah-Hartman
commit f576944a59
1 changed files with 5 additions and 4 deletions
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