Ingo, is this patch acceptable?
On 2018/07/07 22:54, Tetsuo Handa wrote:
>From 61752cef56fad2a910f6bfd277e1b9b028aeab43 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
> Date: Sat, 7 Jul 2018 22:45:30 +0900
> Subject: [PATCH v2] x86: Avoid pr_cont() in show_opcodes()
>
> Since syzbot is confused by concurrent printk() messages [1], this patch
> changes show_opcodes() to use snprintf(). By this change, the Code: line
> will always be printed as one line even if multiple threads concurrently
> called printk().
>
> To save on-stack footprint, this patch shares opcodes[] and buf[] because
> we sequentially reads from opcodes[] and sequentially writes to buf[].
>
> 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-ker...@i-love.skaura.ne.jp>
> Cc: Borislav Petkov <b...@suse.de>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Josh Poimboeuf <jpoim...@redhat.com>
> Cc: Linus Torvalds <torva...@linux-foundation.org>
> Cc: Andy Lutomirski <l...@amacapital.net>
> ---
> arch/x86/kernel/dumpstack.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 666a284..6408123 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -94,25 +94,27 @@ static void printk_stack_address(unsigned long address,
> int reliable,
> void show_opcodes(u8 *rip, const char *loglvl)
> {
> unsigned int code_prologue = OPCODE_BUFSIZE * 2 / 3;
> - u8 opcodes[OPCODE_BUFSIZE];
> u8 *ip;
> int i;
> -
> - printk("%sCode: ", loglvl);
> + int pos = 0;
> + char buf[(3 * OPCODE_BUFSIZE + 2) + 1];
> + u8 *opcodes = (u8 *) buf + sizeof(buf) - OPCODE_BUFSIZE;
>
> 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)
>
