path: root/kernel/debug/kdb
diff options
authorSumit Garg <sumit.garg@linaro.org>2020-06-04 15:31:19 +0530
committerDaniel Thompson <daniel.thompson@linaro.org>2020-06-26 15:40:16 +0100
commit5946d1f5b309381805bad3ddc3054c04f4ae9c24 (patch)
treecc5d93c6b074be806bd226223ebe4ec4fdca9f2c /kernel/debug/kdb
parent2a78b85b70f9c3d450619d369d349ba861320510 (diff)
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 <daniel.thompson@linaro.org> Signed-off-by: Sumit Garg <sumit.garg@linaro.org> Link: https://lore.kernel.org/r/1591264879-25920-5-git-send-email-sumit.garg@linaro.org Reviewed-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Diffstat (limited to 'kernel/debug/kdb')
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 0e4f2eda96d8..683a799618ad 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)
- 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))
+ 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

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