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| H A D | serial_core.c | diff d72402145ace0697a6a9e8e75a3de5bf3375f78d Thu Dec 13 05:58:39 CET 2018 Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> tty/serial: do not free trasnmit buffer page under port lock
LKP has hit yet another circular locking dependency between uart
console drivers and debugobjects [1]:
CPU0 CPU1
rhltable_init()
__init_work()
debug_object_init
uart_shutdown() /* db->lock */
/* uart_port->lock */ debug_print_object()
free_page() printk()
call_console_drivers()
debug_check_no_obj_freed() /* uart_port->lock */
/* db->lock */
debug_print_object()
So there are two dependency chains:
uart_port->lock -> db->lock
And
db->lock -> uart_port->lock
This particular circular locking dependency can be addressed in several
ways:
a) One way would be to move debug_print_object() out of db->lock scope
and, thus, break the db->lock -> uart_port->lock chain.
b) Another one would be to free() transmit buffer page out of db->lock
in UART code; which is what this patch does.
It makes sense to apply a) and b) independently: there are too many things
going on behind free(), none of which depend on uart_port->lock.
The patch fixes transmit buffer page free() in uart_shutdown() and,
additionally, in uart_port_startup() (as was suggested by Dmitry Safonov).
[1] https://lore.kernel.org/lkml/20181211091154.GL23332@shao2-debian/T/#u
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Dmitry Safonov <dima@arista.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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