linux-kernel - [RFC][PATCH v4 -next 4/4] Skip spin_lock of efi_pstore

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Date:	Thu, 5 Jan 2012 12:41:21 -0500
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	"Luck, Tony" <tony.luck@...el.com>, Don Zickus <dzickus@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Brown, Len" <len.brown@...el.com>,
	"'ying.huang@...el.com'" <'ying.huang@...el.com'>,
	"'ak@...ux.intel.com'" <'ak@...ux.intel.com'>,
	"'hughd@...omium.org'" <'hughd@...omium.org'>,
	"'mingo@...e.hu'" <'mingo@...e.hu'>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"namhyung@...il.com" <namhyung@...il.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: [RFC][PATCH v4 -next 4/4] Skip spin_lock of efi_pstore_write() in
 panic case

This patch skips spin_lock of efi_pstore_write() in panic path for these reasons.
 - efi_pstore_write() is serialized via smp_send_stop().
 - SetVariable runtime service is guaranteed to work correctly if you call
   it a second time when you have taken an exception in trying
   to execute them already.

We can avoid deadlock of spin_lock(&efivars->lock) in panic path and get panic log
reliably.


 Signed-off-by: Seiji Aguchi <seiji.aguchi@....com>

---
 drivers/firmware/efivars.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index d25599f..657e6f1 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -510,7 +510,15 @@ static int efi_pstore_write(enum pstore_type_id type,
 	sprintf(stub_name, "dump-type%u-%u-", type, part);
 	sprintf(name, "%s%lu", stub_name, get_seconds());
 
-	spin_lock(&efivars->lock);
+	/*
+	 * We don't need to take any locks in panic path for these reasons.
+	 *  - efi_pstore_write() is serialized via smp_send_stop().
+	 *  - SetVariable runtime service is guaranteed to work correctly
+	 *    if you call it a second time when you have taken an exception
+	 *    in trying to execute them already.
+	 */
+	if (reason != KMSG_DUMP_PANIC)
+		spin_lock(&efivars->lock);
 
 	for (i = 0; i < DUMP_NAME_LEN; i++)
 		efi_name[i] = stub_name[i];
@@ -548,7 +556,8 @@ static int efi_pstore_write(enum pstore_type_id type,
 	efivars->ops->set_variable(efi_name, &vendor, PSTORE_EFI_ATTRIBUTES,
 				   size, psi->buf);
 
-	spin_unlock(&efivars->lock);
+	if (reason != KMSG_DUMP_PANIC)
+		spin_unlock(&efivars->lock);
 
 	if (found)
 		efivar_unregister(found);
-- 
1.7.1



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