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Hui Su
f576944a59
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 <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]/
Reviewed-by: Nam Cao <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
FBTFT ========= Linux Framebuffer drivers for small TFT LCD display modules. The module 'fbtft' makes writing drivers for some of these displays very easy. Development is done on a Raspberry Pi running the Raspbian "wheezy" distribution. For new hardware support consider using DRM subsystem (see TODO). NOTE: The driver is in maintenance mode, only performance issue or bug fixes are accepted, which effectively means the patches must be tested on the real hardware (the patch must be accompanied with the information what hardware is that). The treewide changes may also be accepted as an exception.