netdev - [PATCH V3 08/11] EDAC/altera: Skip the panic notifier if kdump is loaded

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Date:   Fri, 19 Aug 2022 19:17:28 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     akpm@...ux-foundation.org, bhe@...hat.com, pmladek@...e.com,
        kexec@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        netdev@...r.kernel.org, x86@...nel.org, kernel-dev@...lia.com,
        kernel@...ccoli.net, halves@...onical.com, fabiomirmar@...il.com,
        alejandro.j.jimenez@...cle.com, andriy.shevchenko@...ux.intel.com,
        arnd@...db.de, bp@...en8.de, corbet@....net,
        d.hatayama@...fujitsu.com, dave.hansen@...ux.intel.com,
        dyoung@...hat.com, feng.tang@...el.com, gregkh@...uxfoundation.org,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de, keescook@...omium.org,
        luto@...nel.org, mhiramat@...nel.org, mingo@...hat.com,
        paulmck@...nel.org, peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, stern@...land.harvard.edu,
        tglx@...utronix.de, vgoyal@...hat.com, vkuznets@...hat.com,
        will@...nel.org, xuqiang36@...wei.com,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        linux-edac@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
        Dinh Nguyen <dinguyen@...nel.org>
Subject: [PATCH V3 08/11] EDAC/altera: Skip the panic notifier if kdump is loaded

The altera_edac panic notifier performs some data collection with
regards errors detected; such code relies in the regmap layer to
perform reads/writes, so the code is abstracted and there is some
risk level to execute that, since the panic path runs in atomic
context, with interrupts/preemption and secondary CPUs disabled.

Users want the information collected in this panic notifier though,
so in order to balance the risk/benefit, let's skip the altera panic
notifier if kdump is loaded. While at it, remove a useless header
and encompass a macro inside the sole ifdef block it is used.

Cc: Borislav Petkov <bp@...en8.de>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Tony Luck <tony.luck@...el.com>
Acked-by: Dinh Nguyen <dinguyen@...nel.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>

---

V3:
- added the ack tag from Dinh - thanks!
- had a good discussion with Boris about that in V2 [0],
hopefully we can continue and reach a consensus in this V3.
[0] https://lore.kernel.org/lkml/46137c67-25b4-6657-33b7-cffdc7afc0d7@igalia.com/

V2:
- new patch, based on the discussion in [1].
[1] https://lore.kernel.org/lkml/62a63fc2-346f-f375-043a-fa21385279df@igalia.com/


 drivers/edac/altera_edac.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/edac/altera_edac.c b/drivers/edac/altera_edac.c
index e7e8e624a436..741fe5539154 100644
--- a/drivers/edac/altera_edac.c
+++ b/drivers/edac/altera_edac.c
@@ -16,7 +16,6 @@
 #include <linux/kernel.h>
 #include <linux/mfd/altera-sysmgr.h>
 #include <linux/mfd/syscon.h>
-#include <linux/notifier.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
@@ -24,6 +23,7 @@
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
 #include <linux/types.h>
+#include <linux/kexec.h>
 #include <linux/uaccess.h>
 
 #include "altera_edac.h"
@@ -2063,22 +2063,30 @@ static const struct irq_domain_ops a10_eccmgr_ic_ops = {
 };
 
 /************** Stratix 10 EDAC Double Bit Error Handler ************/
-#define to_a10edac(p, m) container_of(p, struct altr_arria10_edac, m)
-
 #ifdef CONFIG_64BIT
 /* panic routine issues reboot on non-zero panic_timeout */
 extern int panic_timeout;
 
+#define to_a10edac(p, m) container_of(p, struct altr_arria10_edac, m)
+
 /*
  * The double bit error is handled through SError which is fatal. This is
  * called as a panic notifier to printout ECC error info as part of the panic.
+ *
+ * Notice that if kdump is set, we take the risk avoidance approach and
+ * skip the notifier, given that users are expected to have access to a
+ * full vmcore.
  */
 static int s10_edac_dberr_handler(struct notifier_block *this,
 				  unsigned long event, void *ptr)
 {
-	struct altr_arria10_edac *edac = to_a10edac(this, panic_notifier);
+	struct altr_arria10_edac *edac;
 	int err_addr, dberror;
 
+	if (kexec_crash_loaded())
+		return NOTIFY_DONE;
+
+	edac = to_a10edac(this, panic_notifier);
 	regmap_read(edac->ecc_mgr_map, S10_SYSMGR_ECC_INTSTAT_DERR_OFST,
 		    &dberror);
 	regmap_write(edac->ecc_mgr_map, S10_SYSMGR_UE_VAL_OFST, dberror);
-- 
2.37.2