From: Sumit Garg <sumit.garg@linaro.org>
To: daniel.thompson@linaro.org
Cc: kgdb-bugreport@lists.sourceforge.net, jason.wessel@windriver.com,
dianders@chromium.org, pmladek@suse.com,
sergey.senozhatsky@gmail.com, gregkh@linuxfoundation.org,
jslaby@suse.com, linux-kernel@vger.kernel.org,
Sumit Garg <sumit.garg@linaro.org>
Subject: [PATCH v5 3/4] kdb: Make kdb_printf() console handling more robust
Date: Wed, 3 Jun 2020 12:52:14 +0530 [thread overview]
Message-ID: <1591168935-6382-4-git-send-email-sumit.garg@linaro.org> (raw)
In-Reply-To: <1591168935-6382-1-git-send-email-sumit.garg@linaro.org>
While rounding up CPUs via NMIs, its possible that a rounded up CPU
maybe holding a console port lock leading to kgdb master CPU stuck in
a deadlock during invocation of console write operations. A similar
deadlock could also be possible while using synchronous breakpoints.
So in order to avoid such a deadlock, set oops_in_progress to encourage
the console drivers to disregard their internal spin locks: in the
current calling context the risk of deadlock is a bigger problem than
risks due to re-entering the console driver. We operate directly on
oops_in_progress rather than using bust_spinlocks() because the calls
bust_spinlocks() makes on exit are not appropriate for this calling
context.
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
---
kernel/debug/kdb/kdb_io.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 58b7d25..0e4f2ed 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -562,7 +562,18 @@ static void kdb_msg_write(const char *msg, int msg_len)
for_each_console(c) {
if (!(c->flags & CON_ENABLED))
continue;
+ /*
+ * Set oops_in_progress to encourage the console drivers to
+ * disregard their internal spin locks: in the current calling
+ * context the risk of deadlock is a bigger problem than risks
+ * due to re-entering the console driver. We operate directly on
+ * oops_in_progress rather than using bust_spinlocks() because
+ * the calls bust_spinlocks() makes on exit are not appropriate
+ * for this calling context.
+ */
+ ++oops_in_progress;
c->write(c, msg, msg_len);
+ --oops_in_progress;
touch_nmi_watchdog();
}
}
--
2.7.4
next prev parent reply other threads:[~2020-06-03 7:22 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-03 7:22 [PATCH v5 0/4] kdb: Improve console handling Sumit Garg
2020-06-03 7:22 ` [PATCH v5 1/4] kdb: Re-factor kdb_printf() message write code Sumit Garg
2020-06-03 8:07 ` Petr Mladek
2020-06-03 7:22 ` [PATCH v5 2/4] kdb: Check status of console prior to invoking handlers Sumit Garg
2020-06-03 8:08 ` Petr Mladek
2020-06-03 7:22 ` Sumit Garg [this message]
2020-06-03 8:10 ` [PATCH v5 3/4] kdb: Make kdb_printf() console handling more robust Petr Mladek
2020-06-03 7:22 ` [PATCH v5 4/4] kdb: Switch to use safer dbg_io_ops over console APIs Sumit Garg
2020-06-03 8:25 ` Petr Mladek
2020-06-03 9:18 ` Daniel Thompson
2020-06-03 11:59 ` Petr Mladek
2020-06-03 9:32 ` Sumit Garg
2020-06-03 11:42 ` Daniel Thompson
2020-06-03 13:05 ` Sumit Garg
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