Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754199AbaDYQeU (ORCPT ); Fri, 25 Apr 2014 12:34:20 -0400 Received: from mail-we0-f177.google.com ([74.125.82.177]:49606 "EHLO mail-we0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751314AbaDYQ3t (ORCPT ); Fri, 25 Apr 2014 12:29:49 -0400 From: Daniel Thompson To: kgdb-bugreport@lists.sourceforge.net, Jason Wessel Cc: patches@linaro.org, linaro-kernel@lists.linaro.org, Daniel Thompson , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Jiri Slaby , Steven Rostedt , Frederic Weisbecker , Ingo Molnar , John Stultz , Anton Vorontsov , Colin Cross , kernel-team@android.com Subject: [RFC v3 1/9] sysrq: Implement __handle_sysrq_nolock to avoid recursive locking in kdb Date: Fri, 25 Apr 2014 17:29:22 +0100 Message-Id: <1398443370-12668-2-git-send-email-daniel.thompson@linaro.org> X-Mailer: git-send-email 1.9.0 In-Reply-To: <1398443370-12668-1-git-send-email-daniel.thompson@linaro.org> References: <1396453440-16445-1-git-send-email-daniel.thompson@linaro.org> <1398443370-12668-1-git-send-email-daniel.thompson@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If kdb is triggered using SysRq-g then any use of the sr command results in the SysRq key table lock being recursively acquired, killing the debug session. That patch resolves the problem by introducing a _nolock alternative for __handle_sysrq. Strictly speaking this approach risks racing on the key table when kdb is triggered by something other than SysRq-g however in that case any other CPU involved should release the spin lock before kgdb parks the slave CPUs. Signed-off-by: Daniel Thompson --- drivers/tty/sysrq.c | 11 ++++++++--- include/linux/sysrq.h | 1 + kernel/debug/kdb/kdb_main.c | 2 +- 3 files changed, 10 insertions(+), 4 deletions(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index ce396ec..7b47b2d 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -505,14 +505,12 @@ static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p) sysrq_key_table[i] = op_p; } -void __handle_sysrq(int key, bool check_mask) +void __handle_sysrq_nolock(int key, bool check_mask) { struct sysrq_key_op *op_p; int orig_log_level; int i; - unsigned long flags; - spin_lock_irqsave(&sysrq_key_table_lock, flags); /* * Raise the apparent loglevel to maximum so that the sysrq header * is shown to provide the user with positive feedback. We do not @@ -554,6 +552,13 @@ void __handle_sysrq(int key, bool check_mask) printk("\n"); console_loglevel = orig_log_level; } +} + +void __handle_sysrq(int key, bool check_mask) +{ + unsigned long flags; + spin_lock_irqsave(&sysrq_key_table_lock, flags); + __handle_sysrq_nolock(key, check_mask); spin_unlock_irqrestore(&sysrq_key_table_lock, flags); } diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h index 387fa7d..1d51d64 100644 --- a/include/linux/sysrq.h +++ b/include/linux/sysrq.h @@ -44,6 +44,7 @@ struct sysrq_key_op { void handle_sysrq(int key); void __handle_sysrq(int key, bool check_mask); +void __handle_sysrq_nolock(int key, bool check_mask); int register_sysrq_key(int key, struct sysrq_key_op *op); int unregister_sysrq_key(int key, struct sysrq_key_op *op); struct sysrq_key_op *__sysrq_get_key_op(int key); diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c index 0b097c8..f39f926 100644 --- a/kernel/debug/kdb/kdb_main.c +++ b/kernel/debug/kdb/kdb_main.c @@ -1924,7 +1924,7 @@ static int kdb_sr(int argc, const char **argv) if (argc != 1) return KDB_ARGCOUNT; kdb_trap_printk++; - __handle_sysrq(*argv[1], false); + __handle_sysrq_nolock(*argv[1], false); kdb_trap_printk--; return 0; -- 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/