linux-kernel - [PATCH 7/9] kexec_core: Add and update comments regarding the KEXEC

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Message-ID: <20241216233704.3208607-8-dwmw2@infradead.org>
Date: Mon, 16 Dec 2024 23:24:14 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Eric Biederman <ebiederm@...ssion.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Sourabh Jain <sourabhjain@...ux.ibm.com>,
	Hari Bathini <hbathini@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>,
	Yuntao Wang <ytcoode@...il.com>,
	David Kaplan <david.kaplan@....com>,
	Tao Liu <ltao@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Breno Leitao <leitao@...ian.org>,
	Wei Yang <richard.weiyang@...il.com>,
	Rong Xu <xur@...gle.com>,
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
	linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org,
	Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	bsz@...zon.de,
	nathan@...nel.org
Subject: [PATCH 7/9] kexec_core: Add and update comments regarding the KEXEC_JUMP flow

From: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>

The KEXEC_JUMP flow is analogous to hibernation flows occurring before
and after creating an image and before and after jumping from the
restore kernel to the image one, which is why it uses the same device
callbacks as those hibernation flows.

Add comments explaining that to the code in question and update an
existing comment in it which appears a bit out of context.

No functional changes.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 kernel/kexec_core.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index c0caa14880c3..7cf8437e0f38 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -1001,6 +1001,12 @@ int kernel_kexec(void)
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (kexec_image->preserve_context) {
+		/*
+		 * This flow is analogous to hibernation flows that occur before
+		 * creating an image and before jumping from the restore kernel
+		 * to the image one, so it uses the same device device callbacks
+		 * as those two flows.
+		 */
 		pm_prepare_console();
 		error = freeze_processes();
 		if (error) {
@@ -1011,12 +1017,10 @@ int kernel_kexec(void)
 		error = dpm_suspend_start(PMSG_FREEZE);
 		if (error)
 			goto Resume_console;
-		/* At this point, dpm_suspend_start() has been called,
-		 * but *not* dpm_suspend_end(). We *must* call
-		 * dpm_suspend_end() now.  Otherwise, drivers for
-		 * some devices (e.g. interrupt controllers) become
-		 * desynchronized with the actual state of the
-		 * hardware at resume time, and evil weirdness ensues.
+		/*
+		 * dpm_suspend_end() must be called after dpm_suspend_start()
+		 * to complete the transition, like in the hibernation flows
+		 * mentioned above.
 		 */
 		error = dpm_suspend_end(PMSG_FREEZE);
 		if (error)
@@ -1052,6 +1056,13 @@ int kernel_kexec(void)
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (kexec_image->preserve_context) {
+		/*
+		 * This flow is analogous to hibernation flows that occur after
+		 * creating an image and after the image hernel has got control
+		 * back, and in case the devices have been reset or otherwise
+		 * manipulated in the meantime, it uses the device callbacks
+		 * used by the latter.
+		 */
 		syscore_resume();
  Enable_irqs:
 		local_irq_enable();
-- 
2.47.0