linux-kernel - [PATCH RESEND v2] kexec/crash: no crash update when kexec in progress

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Message-ID: <20240911112111.108056-1-sourabhjain@linux.ibm.com>
Date: Wed, 11 Sep 2024 16:51:11 +0530
From: Sourabh Jain <sourabhjain@...ux.ibm.com>
To: bhe@...hat.com
Cc: Hari Bathini <hbathini@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, Sachin P Bappalige <sachinpb@...ux.vnet.ibm.com>
Subject: [PATCH RESEND v2] kexec/crash: no crash update when kexec in progress

The following errors are observed when kexec is done with SMT=off on
powerpc.

[  358.458385] Removing IBM Power 842 compression device
[  374.795734] kexec_core: Starting new kernel
[  374.795748] kexec: Waking offline cpu 1.
[  374.875695] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
[  374.935833] kexec: Waking offline cpu 2.
[  375.015664] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
snip..
[  375.515823] kexec: Waking offline cpu 6.
[  375.635667] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
[  375.695836] kexec: Waking offline cpu 7.

To avoid kexec kernel boot failure on PowerPC, all the present CPUs that
are offline are brought online during kexec. For more information, refer
to commit e8e5c2155b00 ("powerpc/kexec: Fix orphaned offline CPUs across
kexec"). Bringing the CPUs online triggers the crash hotplug handler,
crash_handle_hotplug_event(), to update the kdump image. Since the
system is on the kexec kernel boot path and the kexec lock is held, the
crash_handle_hotplug_event() function fails to acquire the same lock to
update the kdump image, resulting in the error messages mentioned above.

To fix this, return from crash_handle_hotplug_event() without printing
the error message if kexec is in progress.

The same applies to the crash_check_hotplug_support() function. Return
0 if kexec is in progress because kernel is not in a position to update
the kdump image.

Cc: Hari Bathini <hbathini@...ux.ibm.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: kexec@...ts.infradead.org
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: linux-kernel@...r.kernel.org
Cc: x86@...nel.org
Reported-by: Sachin P Bappalige <sachinpb@...ux.vnet.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
---
Changelog:

Since v1:
 - Keep the kexec_in_progress check within kexec_trylock() - Baoquan He
 - Include the reason why PowerPC brings offline CPUs online
   during the kexec kernel boot path - Baoquan He
 - Rebased on top of #next-20240910 to avoid conflict with the patch below
   https://lore.kernel.org/all/20240812041651.703156-1-sourabhjain@linux.ibm.com/T/#u

V2 RESEND:
 - Update linuxppc-dev mailing list address
---
 kernel/crash_core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index c1048893f4b6..078fe5bc5a74 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -505,7 +505,8 @@ int crash_check_hotplug_support(void)
 	crash_hotplug_lock();
 	/* Obtain lock while reading crash information */
 	if (!kexec_trylock()) {
-		pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
+		if (!kexec_in_progress)
+			pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
 		crash_hotplug_unlock();
 		return 0;
 	}
@@ -547,7 +548,8 @@ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu,
 	crash_hotplug_lock();
 	/* Obtain lock while changing crash information */
 	if (!kexec_trylock()) {
-		pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
+		if (!kexec_in_progress)
+			pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
 		crash_hotplug_unlock();
 		return;
 	}
-- 
2.46.0