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kdb: Switch to use safer dbg_io_ops over console APIs

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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>
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>
This commit is contained in:
Sumit Garg
2020-06-04 15:31:19 +05:30
committed by Daniel Thompson
parent 2a78b85b70
commit 5946d1f5b3
5 changed files with 24 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
kernel/debug/kdb/kdb_io.c
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@@ -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