linux-kernel - Re: linux-next: Tree for Aug 1

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Date:   Tue, 1 Aug 2017 21:42:04 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: linux-next: Tree for Aug 1

Hello,


seems that commit 979990c6284814617 ("tty: improve tty_insert_flip_char()
fast path") panics my kernel.

in particular, this part

@@ -26,7 +27,7 @@ static inline int tty_insert_flip_char(struct tty_port *port,
                *char_buf_ptr(tb, tb->used++) = ch;
                return 1;
        }
-       return tty_insert_flip_string_flags(port, &ch, &flag, 1);
+       return __tty_insert_flip_char(port, ch, flag);
 }



I see various callstacks, but all endup in llist_del_first() -> fatal exception
in interrupt -> panic()


...
uart_insert_char()
  __tty_insert_flip_char()
    __tty_buffer_request_room()
      llist_del_first()

or

...
kdb_event()
  puts_queue()
    __tty_insert_flip_char()
      __tty_buffer_request_room()
        llist_del_first()



to reproduce:

1) screen /dev/ttyS0 115200
2) send several chars down to /dev/ttyS0, enough to panic() the kernel.


reverting that __tty_insert_flip_char(port, ch, flag) seems to work
on my side.

	-ss