From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934040AbcI3PUA (ORCPT ); Fri, 30 Sep 2016 11:20:00 -0400 Received: from mail-pa0-f66.google.com ([209.85.220.66]:34804 "EHLO mail-pa0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933921AbcI3PT0 (ORCPT ); Fri, 30 Sep 2016 11:19:26 -0400 From: Sergey Senozhatsky To: Petr Mladek , Jan Kara Cc: Andrew Morton , Tejun Heo , Calvin Owens , Thomas Gleixner , Mel Gorman , Steven Rostedt , linux-kernel@vger.kernel.org, Sergey Senozhatsky , Sergey Senozhatsky Subject: [RFC][PATCHv2 6/7] printk: report printk recursion from alt_printk flush Date: Sat, 1 Oct 2016 00:17:57 +0900 Message-Id: <20160930151758.8965-7-sergey.senozhatsky@gmail.com> X-Mailer: git-send-email 2.10.0.372.g6fe1b14 In-Reply-To: <20160930151758.8965-1-sergey.senozhatsky@gmail.com> References: <20160930151758.8965-1-sergey.senozhatsky@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we end up executing vprintk_alt() then we have a printk recursion. Set alt_printk_ctx `ALT_PRINTK_RECURSION_MASK' bit in vprintk_alt() to indicate that recutsion and report the "BUG: recent printk recursion!" problem later from __alt_printk_flush(). Example: BUG: recent printk recursion! ------------[ cut here ]------------ WARNING: CPU: 3 PID: 366 at kernel/printk/printk.c:1803 vprintk_emit+0x139/0x38c CPU: 3 PID: 366 Comm: bash Call Trace: [] dump_stack+0x4d/0x63 [] __warn+0xb8/0xd3 [] warn_slowpath_null+0x18/0x1a [] vprintk_emit+0x139/0x38c [] vprintk_default+0x18/0x1a [] vprintk_func+0x65/0x67 [] printk+0x3e/0x46 [..] [] entry_SYSCALL_64_fastpath+0x13/0x94 ---[ end trace ]--- Signed-off-by: Sergey Senozhatsky --- kernel/printk/alt_printk.c | 9 +++++++++ kernel/printk/internal.h | 1 + 2 files changed, 10 insertions(+) diff --git a/kernel/printk/alt_printk.c b/kernel/printk/alt_printk.c index db0bfc8..0010089 100644 --- a/kernel/printk/alt_printk.c +++ b/kernel/printk/alt_printk.c @@ -150,6 +150,13 @@ static void __alt_printk_flush(struct irq_work *work) more: len = atomic_read(&s->len); + if (this_cpu_read(alt_printk_ctx) & ALT_PRINTK_RECURSION_MASK) { + const char *msg = "BUG: recent printk recursion!\n"; + + this_cpu_and(alt_printk_ctx, ~ALT_PRINTK_RECURSION_MASK); + alt_printk_flush_line(msg, strlen(msg)); + } + /* * This is just a paranoid check that nobody has manipulated * the buffer an unexpected way. If we printed something then @@ -290,6 +297,8 @@ static int vprintk_alt(const char *fmt, va_list args) { struct alt_printk_seq_buf *s = this_cpu_ptr(&alt_print_seq); + /* There is only one way to get here -- a printk recursion. */ + this_cpu_or(alt_printk_ctx, ALT_PRINTK_RECURSION_MASK); return alt_printk_log_store(s, fmt, args); } diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h index 6338f5b..403b6ed 100644 --- a/kernel/printk/internal.h +++ b/kernel/printk/internal.h @@ -37,6 +37,7 @@ static inline int get_nmi_message_lost(void) #define ALT_PRINTK_CONTEXT_MASK 0x07ffffff #define ALT_PRINTK_NMI_CONTEXT_MASK 0x08000000 +#define ALT_PRINTK_RECURSION_MASK 0x10000000 extern raw_spinlock_t logbuf_lock; -- 2.10.0.372.g6fe1b14