From 5946d1f5b309381805bad3ddc3054c04f4ae9c24 Mon Sep 17 00:00:00 2001 From: Sumit Garg Date: Thu, 4 Jun 2020 15:31:19 +0530 Subject: kdb: Switch to use safer dbg_io_ops over console APIs In kgdb context, calling console handlers aren't safe due to locks used in those handlers which could in turn lead to a deadlock. Although, using oops_in_progress increases the chance to bypass locks in most console handlers but it might not be sufficient enough in case a console uses more locks (VT/TTY is good example). Currently when a driver provides both polling I/O and a console then kdb will output using the console. We can increase robustness by using the currently active polling I/O driver (which should be lockless) instead of the corresponding console. For several common cases (e.g. an embedded system with a single serial port that is used both for console output and debugger I/O) this will result in no console handler being used. In order to achieve this we need to reverse the order of preference to use dbg_io_ops (uses polling I/O mode) over console APIs. So we just store "struct console" that represents debugger I/O in dbg_io_ops and while emitting kdb messages, skip console that matches dbg_io_ops console in order to avoid duplicate messages. After this change, "is_console" param becomes redundant and hence removed. Suggested-by: Daniel Thompson Signed-off-by: Sumit Garg Link: https://lore.kernel.org/r/1591264879-25920-5-git-send-email-sumit.garg@linaro.org Reviewed-by: Douglas Anderson Reviewed-by: Petr Mladek Acked-by: Greg Kroah-Hartman Signed-off-by: Daniel Thompson --- drivers/tty/serial/kgdboc.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) (limited to 'drivers/tty/serial/kgdboc.c') diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 41396982e9e0..84ffede27f23 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -45,7 +45,6 @@ static struct platform_device *kgdboc_pdev; #if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) static struct kgdb_io kgdboc_earlycon_io_ops; -static struct console *earlycon; static int (*earlycon_orig_exit)(struct console *con); #endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */ @@ -145,7 +144,7 @@ static void kgdboc_unregister_kbd(void) #if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) static void cleanup_earlycon(void) { - if (earlycon) + if (kgdboc_earlycon_io_ops.cons) kgdb_unregister_io_module(&kgdboc_earlycon_io_ops); } #else /* !IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */ @@ -178,7 +177,7 @@ static int configure_kgdboc(void) goto noconfig; } - kgdboc_io_ops.is_console = 0; + kgdboc_io_ops.cons = NULL; kgdb_tty_driver = NULL; kgdboc_use_kms = 0; @@ -198,7 +197,7 @@ static int configure_kgdboc(void) int idx; if (cons->device && cons->device(cons, &idx) == p && idx == tty_line) { - kgdboc_io_ops.is_console = 1; + kgdboc_io_ops.cons = cons; break; } } @@ -433,7 +432,8 @@ static int kgdboc_earlycon_get_char(void) { char c; - if (!earlycon->read(earlycon, &c, 1)) + if (!kgdboc_earlycon_io_ops.cons->read(kgdboc_earlycon_io_ops.cons, + &c, 1)) return NO_POLL_CHAR; return c; @@ -441,7 +441,8 @@ static int kgdboc_earlycon_get_char(void) static void kgdboc_earlycon_put_char(u8 chr) { - earlycon->write(earlycon, &chr, 1); + kgdboc_earlycon_io_ops.cons->write(kgdboc_earlycon_io_ops.cons, &chr, + 1); } static void kgdboc_earlycon_pre_exp_handler(void) @@ -461,7 +462,7 @@ static void kgdboc_earlycon_pre_exp_handler(void) * boot if we detect this case. */ for_each_console(con) - if (con == earlycon) + if (con == kgdboc_earlycon_io_ops.cons) return; already_warned = true; @@ -484,25 +485,25 @@ static int kgdboc_earlycon_deferred_exit(struct console *con) static void kgdboc_earlycon_deinit(void) { - if (!earlycon) + if (!kgdboc_earlycon_io_ops.cons) return; - if (earlycon->exit == kgdboc_earlycon_deferred_exit) + if (kgdboc_earlycon_io_ops.cons->exit == kgdboc_earlycon_deferred_exit) /* * kgdboc_earlycon is exiting but original boot console exit * was never called (AKA kgdboc_earlycon_deferred_exit() * didn't ever run). Undo our trap. */ - earlycon->exit = earlycon_orig_exit; - else if (earlycon->exit) + kgdboc_earlycon_io_ops.cons->exit = earlycon_orig_exit; + else if (kgdboc_earlycon_io_ops.cons->exit) /* * We skipped calling the exit() routine so we could try to * keep using the boot console even after it went away. We're * finally done so call the function now. */ - earlycon->exit(earlycon); + kgdboc_earlycon_io_ops.cons->exit(kgdboc_earlycon_io_ops.cons); - earlycon = NULL; + kgdboc_earlycon_io_ops.cons = NULL; } static struct kgdb_io kgdboc_earlycon_io_ops = { @@ -511,7 +512,6 @@ static struct kgdb_io kgdboc_earlycon_io_ops = { .write_char = kgdboc_earlycon_put_char, .pre_exception = kgdboc_earlycon_pre_exp_handler, .deinit = kgdboc_earlycon_deinit, - .is_console = true, }; #define MAX_CONSOLE_NAME_LEN (sizeof((struct console *) 0)->name) @@ -557,10 +557,10 @@ static int __init kgdboc_earlycon_init(char *opt) goto unlock; } - earlycon = con; + kgdboc_earlycon_io_ops.cons = con; pr_info("Going to register kgdb with earlycon '%s'\n", con->name); if (kgdb_register_io_module(&kgdboc_earlycon_io_ops) != 0) { - earlycon = NULL; + kgdboc_earlycon_io_ops.cons = NULL; pr_info("Failed to register kgdb with earlycon\n"); } else { /* Trap exit so we can keep earlycon longer if needed. */ -- cgit v1.2.3-59-g8ed1b