linux-kernel - [PATCH 8/9] s390/bug: Skip __WARN

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Message-ID: <20251209121701.1856271-9-hca@linux.ibm.com>
Date: Tue,  9 Dec 2025 13:17:00 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>, Arnd Bergmann <arnd@...db.de>,
        Jens Remus <jremus@...ux.ibm.com>,
        Stefan Schulze Frielinghaus <stefansf@...ux.ibm.com>,
        Juergen Christ <jchrist@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: [PATCH 8/9] s390/bug: Skip __WARN_trap() in call traces

In order to avoid rather pointless warning disassemblies of __WARN_trap()
set the PSW address to the return address of the function which called
__WARN_trap(). This is the address to which __WARN_trap() would return
in any case.

The result is a disassembly of the function which called __WARN_trap(),
which is much more helpful.

Before:

WARNING: arch/s390/kernel/setup.c:1017 at foobar+0x2c/0x20, CPU#0: swapper/0/0
...
Krnl PSW : 0704c00180000000 000003ffe0f675f4 (__WARN_trap+0x4/0x10)
...
Krnl Code: 000003ffe0f675ec: 0707                bcr     0,%r7
           000003ffe0f675ee: 0707                bcr     0,%r7
          *000003ffe0f675f0: af000001            mc      1,0
          >000003ffe0f675f4: 07fe                bcr     15,%r14
           000003ffe0f675f6: 47000700            bc      0,1792
           000003ffe0f675fa: 0707                bcr     0,%r7
           000003ffe0f675fc: 0707                bcr     0,%r7
           000003ffe0f675fe: 0707                bcr     0,%r7
Call Trace:
 [<000003ffe0f675f4>] __WARN_trap+0x4/0x10
 [<000003ffe185bc2e>] arch_cpu_finalize_init+0x26/0x60
 [<000003ffe185654c>] start_kernel+0x53c/0x5d8
 [<000003ffe010002e>] startup_continue+0x2e/0x40

Afterwards:

WARNING: arch/s390/kernel/setup.c:1017 at foobar+0x12/0x30, CPU#0: swapper/0/0
...
Krnl PSW : 0704c00180000000 000003ffe185bc2e (arch_cpu_finalize_init+0x26/0x60)
...
Krnl Code: 000003ffe185bc1c: e3f0ff98ff71        lay     %r15,-104(%r15)
           000003ffe185bc22: e3e0f0980024        stg     %r14,152(%r15)
          *000003ffe185bc28: c0e5ff45ed94        brasl   %r14,000003ffe0119750
          >000003ffe185bc2e: c0e5ffa052b9        brasl   %r14,000003ffe0c661a0
           000003ffe185bc34: c020fffe86d6        larl    %r2,000003ffe182c9e0
           000003ffe185bc3a: e548f0a80006        mvghi   168(%r15),6
           000003ffe185bc40: e548f0a00005        mvghi   160(%r15),5
           000003ffe185bc46: a7690004            lghi    %r6,4
Call Trace:
 [<000003ffe185bc2e>] arch_cpu_finalize_init+0x26/0x60
 [<000003ffe185654c>] start_kernel+0x53c/0x5d8
 [<000003ffe010002e>] startup_continue+0x2e/0x40

Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
---
 arch/s390/kernel/traps.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
index 8aca5858b403..5ed6ebe823bd 100644
--- a/arch/s390/kernel/traps.c
+++ b/arch/s390/kernel/traps.c
@@ -252,10 +252,12 @@ static void monitor_event_exception(struct pt_regs *regs)
 
 	if (user_mode(regs))
 		return;
-	if (regs->monitor_code == MONCODE_BUG_ARG)
+	if (regs->monitor_code == MONCODE_BUG_ARG) {
+		regs->psw.addr = regs->gprs[14];
 		btt = report_bug_entry((struct bug_entry *)regs->gprs[2], regs);
-	else
+	} else {
 		btt = report_bug(regs->psw.addr - (regs->int_code >> 16), regs);
+	}
 	switch (btt) {
 	case BUG_TRAP_TYPE_NONE:
 		fixup_exception(regs);
-- 
2.51.0