From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E3EFEB64DD for ; Wed, 9 Aug 2023 11:07:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233118AbjHILG7 (ORCPT ); Wed, 9 Aug 2023 07:06:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47458 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233144AbjHILG5 (ORCPT ); Wed, 9 Aug 2023 07:06:57 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18D061724 for ; Wed, 9 Aug 2023 04:06:57 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A311762BD5 for ; Wed, 9 Aug 2023 11:06:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0F5FC433C8; Wed, 9 Aug 2023 11:06:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1691579216; bh=wVIFm+c24cNwlC5s5rWH9/DEdjQ+6jthcsPCVtEmbwQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YJ7k0atnCDVTiLutu9kstMUU0KoiXccP9GI2ZgO43qDPCQof/j1lEUgkRO7dhwqmL tW+CMSYTaod2rNScLxWXtoEqc/yx7yvseTB4Kec8X6Wq1eFmJSpppJ7ij3X/H/aLxD SnDpaimo/E5NcxZEzjPUeGuuc2fivgal/U27Av4w= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Zheng Yejian , "Steven Rostedt (Google)" Subject: [PATCH 4.14 117/204] ring-buffer: Fix deadloop issue on reading trace_pipe Date: Wed, 9 Aug 2023 12:40:55 +0200 Message-ID: <20230809103646.518518590@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230809103642.552405807@linuxfoundation.org> References: <20230809103642.552405807@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Zheng Yejian commit 7e42907f3a7b4ce3a2d1757f6d78336984daf8f5 upstream. Soft lockup occurs when reading file 'trace_pipe': watchdog: BUG: soft lockup - CPU#6 stuck for 22s! [cat:4488] [...] RIP: 0010:ring_buffer_empty_cpu+0xed/0x170 RSP: 0018:ffff88810dd6fc48 EFLAGS: 00000246 RAX: 0000000000000000 RBX: 0000000000000246 RCX: ffffffff93d1aaeb RDX: ffff88810a280040 RSI: 0000000000000008 RDI: ffff88811164b218 RBP: ffff88811164b218 R08: 0000000000000000 R09: ffff88815156600f R10: ffffed102a2acc01 R11: 0000000000000001 R12: 0000000051651901 R13: 0000000000000000 R14: ffff888115e49500 R15: 0000000000000000 [...] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8d853c2000 CR3: 000000010dcd8000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: __find_next_entry+0x1a8/0x4b0 ? peek_next_entry+0x250/0x250 ? down_write+0xa5/0x120 ? down_write_killable+0x130/0x130 trace_find_next_entry_inc+0x3b/0x1d0 tracing_read_pipe+0x423/0xae0 ? tracing_splice_read_pipe+0xcb0/0xcb0 vfs_read+0x16b/0x490 ksys_read+0x105/0x210 ? __ia32_sys_pwrite64+0x200/0x200 ? switch_fpu_return+0x108/0x220 do_syscall_64+0x33/0x40 entry_SYSCALL_64_after_hwframe+0x61/0xc6 Through the vmcore, I found it's because in tracing_read_pipe(), ring_buffer_empty_cpu() found some buffer is not empty but then it cannot read anything due to "rb_num_of_entries() == 0" always true, Then it infinitely loop the procedure due to user buffer not been filled, see following code path: tracing_read_pipe() { ... ... waitagain: tracing_wait_pipe() // 1. find non-empty buffer here trace_find_next_entry_inc() // 2. loop here try to find an entry __find_next_entry() ring_buffer_empty_cpu(); // 3. find non-empty buffer peek_next_entry() // 4. but peek always return NULL ring_buffer_peek() rb_buffer_peek() rb_get_reader_page() // 5. because rb_num_of_entries() == 0 always true here // then return NULL // 6. user buffer not been filled so goto 'waitgain' // and eventually leads to an deadloop in kernel!!! } By some analyzing, I found that when resetting ringbuffer, the 'entries' of its pages are not all cleared (see rb_reset_cpu()). Then when reducing the ringbuffer, and if some reduced pages exist dirty 'entries' data, they will be added into 'cpu_buffer->overrun' (see rb_remove_pages()), which cause wrong 'overrun' count and eventually cause the deadloop issue. To fix it, we need to clear every pages in rb_reset_cpu(). Link: https://lore.kernel.org/linux-trace-kernel/20230708225144.3785600-1-zhengyejian1@huawei.com Cc: stable@vger.kernel.org Fixes: a5fb833172eca ("ring-buffer: Fix uninitialized read_stamp") Signed-off-by: Zheng Yejian Signed-off-by: Steven Rostedt (Google) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/ring_buffer.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -4277,28 +4277,34 @@ unsigned long ring_buffer_size(struct ri } EXPORT_SYMBOL_GPL(ring_buffer_size); +static void rb_clear_buffer_page(struct buffer_page *page) +{ + local_set(&page->write, 0); + local_set(&page->entries, 0); + rb_init_page(page->page); + page->read = 0; +} + static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer) { + struct buffer_page *page; + rb_head_page_deactivate(cpu_buffer); cpu_buffer->head_page = list_entry(cpu_buffer->pages, struct buffer_page, list); - local_set(&cpu_buffer->head_page->write, 0); - local_set(&cpu_buffer->head_page->entries, 0); - local_set(&cpu_buffer->head_page->page->commit, 0); - - cpu_buffer->head_page->read = 0; + rb_clear_buffer_page(cpu_buffer->head_page); + list_for_each_entry(page, cpu_buffer->pages, list) { + rb_clear_buffer_page(page); + } cpu_buffer->tail_page = cpu_buffer->head_page; cpu_buffer->commit_page = cpu_buffer->head_page; INIT_LIST_HEAD(&cpu_buffer->reader_page->list); INIT_LIST_HEAD(&cpu_buffer->new_pages); - local_set(&cpu_buffer->reader_page->write, 0); - local_set(&cpu_buffer->reader_page->entries, 0); - local_set(&cpu_buffer->reader_page->page->commit, 0); - cpu_buffer->reader_page->read = 0; + rb_clear_buffer_page(cpu_buffer->reader_page); local_set(&cpu_buffer->entries_bytes, 0); local_set(&cpu_buffer->overrun, 0);