Messages in this thread Patch in this message | | | From | Sumit Garg <> | Subject | [PATCH v5 4/4] kdb: Switch to use safer dbg_io_ops over console APIs | Date | Wed, 3 Jun 2020 12:52:15 +0530 |
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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 <daniel.thompson@linaro.org> Signed-off-by: Sumit Garg <sumit.garg@linaro.org> Reviewed-by: Douglas Anderson <dianders@chromium.org> --- drivers/tty/serial/kgdb_nmi.c | 2 +- drivers/tty/serial/kgdboc.c | 6 +++--- drivers/usb/early/ehci-dbgp.c | 3 ++- include/linux/kgdb.h | 5 ++--- kernel/debug/kdb/kdb_io.c | 4 +++- 5 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c index 5022447..6004c0c 100644 --- a/drivers/tty/serial/kgdb_nmi.c +++ b/drivers/tty/serial/kgdb_nmi.c @@ -50,7 +50,7 @@ static int kgdb_nmi_console_setup(struct console *co, char *options) * I/O utilities that messages sent to the console will automatically * be displayed on the dbg_io. */ - dbg_io_ops->is_console = true; + dbg_io_ops->cons = co; return 0; } diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 4139698..6e182aa 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -178,7 +178,7 @@ 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 +198,7 @@ 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; } } @@ -511,7 +511,6 @@ 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) @@ -558,6 +557,7 @@ static int __init kgdboc_earlycon_init(char *opt) } 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; diff --git a/drivers/usb/early/ehci-dbgp.c b/drivers/usb/early/ehci-dbgp.c index ea0d531..775cf70 100644 --- a/drivers/usb/early/ehci-dbgp.c +++ b/drivers/usb/early/ehci-dbgp.c @@ -1058,7 +1058,8 @@ static int __init kgdbdbgp_parse_config(char *str) kgdbdbgp_wait_time = simple_strtoul(ptr, &ptr, 10); } kgdb_register_io_module(&kgdbdbgp_io_ops); - kgdbdbgp_io_ops.is_console = early_dbgp_console.index != -1; + if (early_dbgp_console.index != -1) + kgdbdbgp_io_ops.cons = &early_dbgp_console; return 0; } diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h index c62d764..529116b 100644 --- a/include/linux/kgdb.h +++ b/include/linux/kgdb.h @@ -276,8 +276,7 @@ struct kgdb_arch { * the I/O driver. * @post_exception: Pointer to a function that will do any cleanup work * for the I/O driver. - * @is_console: 1 if the end device is a console 0 if the I/O device is - * not a console + * @cons: valid if the I/O device is a console; else NULL. */ struct kgdb_io { const char *name; @@ -288,7 +287,7 @@ struct kgdb_io { void (*deinit) (void); void (*pre_exception) (void); void (*post_exception) (void); - int is_console; + struct console *cons; }; extern const struct kgdb_arch arch_kgdb_ops; diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c index 0e4f2ed..683a799 100644 --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -549,7 +549,7 @@ static void kdb_msg_write(const char *msg, int msg_len) if (msg_len == 0) return; - if (dbg_io_ops && !dbg_io_ops->is_console) { + if (dbg_io_ops) { const char *cp = msg; int len = msg_len; @@ -562,6 +562,8 @@ static void kdb_msg_write(const char *msg, int msg_len) for_each_console(c) { if (!(c->flags & CON_ENABLED)) continue; + if (c == dbg_io_ops->cons) + continue; /* * Set oops_in_progress to encourage the console drivers to * disregard their internal spin locks: in the current calling -- 2.7.4
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