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Subject[PATCH] x86: Avoid pr_cont() in show_opcodes()
Date
From: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>

Since syzbot is confused by concurrent printk() messages [1],
this patch changes show_opcodes() to use snprintf().

When we start adding prefix to each line of printk() output,
we will be able to handle concurrent printk() messages.

[1] https://syzkaller.appspot.com/text?tag=CrashReport&x=139d342c400000

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SKAURA.ne.jp>
Cc: Borislav Petkov <bp@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
---
arch/x86/kernel/dumpstack.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 666a284..bb47426 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -97,22 +97,24 @@ void show_opcodes(u8 *rip, const char *loglvl)
u8 opcodes[OPCODE_BUFSIZE];
u8 *ip;
int i;
-
- printk("%sCode: ", loglvl);
+ int pos = 0;
+ char buf[(3 * OPCODE_BUFSIZE + 2) + 1];

ip = (u8 *)rip - code_prologue;
if (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) {
- pr_cont("Bad RIP value.\n");
+ printk("%sCode: Bad RIP value.\n", loglvl);
return;
}

for (i = 0; i < OPCODE_BUFSIZE; i++, ip++) {
if (ip == rip)
- pr_cont("<%02x> ", opcodes[i]);
+ pos += snprintf(buf + pos, sizeof(buf) - pos,
+ "<%02x> ", opcodes[i]);
else
- pr_cont("%02x ", opcodes[i]);
+ pos += snprintf(buf + pos, sizeof(buf) - pos,
+ "%02x ", opcodes[i]);
}
- pr_cont("\n");
+ printk("%sCode: %s\n", loglvl, buf);
}

void show_ip(struct pt_regs *regs, const char *loglvl)
--
2.7.4
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