From nobody Fri Apr 17 03:11:59 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 178762F12AF; Tue, 24 Feb 2026 06:52:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771915965; cv=none; b=EkDeu70x8/Lh9HWGvYDzOi8gay1ODohXXjAl64UBVLDNp8d2OeLim0C+culn+r88EP6DOSh97/1nOtJskPvNZpVHOALNbm1i6NuiXt+evl+oXEG2CaYdRTniPooeZNOEdlgXQ3dt+KbOSkinG9kNSFz62S6tmhcDsAvi4RsgFK8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771915965; c=relaxed/simple; bh=gypdpJkmcV6D/oJuk2s7QT1S/EzyTDFnk0l2rLqc3+8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Z0SY26iVXHY0Ycnx1QEPugkc9kMtHHr3Msgj4xugsFZMJuHVg46+k3aj+yF8Q04eTVwZ3O2Tpsr0kIOO3Dh0IGp9viaGzOAikrKVtVfoXH+dBwB8AYQnyVigu1dOJ8X99ClnIsmrjRhOtZBVx1axzjfy/V8vUhsBHt+sNfNjbPM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rwIVbHOC; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="rwIVbHOC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECEEEC116D0; Tue, 24 Feb 2026 06:52:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771915964; bh=gypdpJkmcV6D/oJuk2s7QT1S/EzyTDFnk0l2rLqc3+8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rwIVbHOCu4jNOt09DFeazLcwRxXkxkNUGUWHXEVkjk5DJdsgF/BNwER5iRimIK7v3 M3J3tFZ5tQezlfGttzWprvfMdua8ZxxwI3yXzdKUJQQlcnXEVNyDbdUIBb9OFjMcgX BR33/csPTXYgBTxROSWBaRxN+M1WvCZClHJJC0feqpGNjy2wiF0DZhRezTtT5TmoP+ dIEU66uKrCI9iWe4FwHVqIkqcFhp6AAITcjq18qoTsOuVnnswNSAFD0KpVc4gufqzy i21Q0mXIH2+/h+qmdJTIwsC/m8NCoLexsDiBI4YCNWKCN9xFYEQefU8BbVeckJCN3o dYjxSahPMkJ4Q== From: "Masami Hiramatsu (Google)" To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH v4 1/3] ring-buffer: Flush and stop persistent ring buffer on panic Date: Tue, 24 Feb 2026 15:52:42 +0900 Message-ID: <177191596224.435720.8250761603256925623.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.53.0.371.g1d285c8824-goog In-Reply-To: <177191595057.435720.10116014529518464418.stgit@mhiramat.tok.corp.google.com> References: <177191595057.435720.10116014529518464418.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) On real hardware, panic and machine reboot may not flush hardware cache to memory. This means the persistent ring buffer, which relies on a coherent state of memory, may not have its events written to the buffer and they may be lost. Moreover, there may be inconsistency with the counters which are used for validation of the integrity of the persistent ring buffer which may cause all data to be discarded. To avoid this issue, stop recording of the ring buffer on panic and flush the cache of the ring buffer's memory. Fixes: e645535a954a ("tracing: Add option to use memmapped memory for trace= boot instance") Cc: stable@vger.kernel.org Signed-off-by: Masami Hiramatsu (Google) --- Changes in v3: - update patch description. --- kernel/trace/ring_buffer.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f16f053ef77d..3eb124c93d72 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6,6 +6,7 @@ */ #include #include +#include #include #include #include @@ -589,6 +590,7 @@ struct trace_buffer { =20 unsigned long range_addr_start; unsigned long range_addr_end; + struct notifier_block flush_nb; =20 struct ring_buffer_meta *meta; =20 @@ -2471,6 +2473,16 @@ static void rb_free_cpu_buffer(struct ring_buffer_pe= r_cpu *cpu_buffer) kfree(cpu_buffer); } =20 +static int rb_flush_buffer_cb(struct notifier_block *nb, unsigned long eve= nt, void *data) +{ + struct trace_buffer *buffer =3D container_of(nb, struct trace_buffer, flu= sh_nb); + + ring_buffer_record_disable(buffer); + flush_kernel_vmap_range((void *)buffer->range_addr_start, + buffer->range_addr_end - buffer->range_addr_start); + return NOTIFY_DONE; +} + static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flag= s, int order, unsigned long start, unsigned long end, @@ -2590,6 +2602,12 @@ static struct trace_buffer *alloc_buffer(unsigned lo= ng size, unsigned flags, =20 mutex_init(&buffer->mutex); =20 + /* Persistent ring buffer needs to flush cache before reboot. */ + if (start & end) { + buffer->flush_nb.notifier_call =3D rb_flush_buffer_cb; + atomic_notifier_chain_register(&panic_notifier_list, &buffer->flush_nb); + } + return_ptr(buffer); =20 fail_free_buffers: @@ -2677,6 +2695,9 @@ ring_buffer_free(struct trace_buffer *buffer) { int cpu; =20 + if (buffer->range_addr_start && buffer->range_addr_end) + atomic_notifier_chain_unregister(&panic_notifier_list, &buffer->flush_nb= ); + cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node); =20 irq_work_sync(&buffer->irq_work.work); From nobody Fri Apr 17 03:11:59 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B1C272F12AF; Tue, 24 Feb 2026 06:52:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771915972; cv=none; b=nbHvp+UBqfVlgBPpDURPwzs341HUykWQmtK8i4dVOc+PV4sXXUF7ACPefsKH42T0BjNPfftjqFvLCjs6Wwpml7JuuExBBpt4pklyx97afVdLlI1BKWg4YECWVCN7GKMBxhbY0kJDD9zO9sACYQWRKU6ehc8Hw2fpwdGxgZW1W14= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771915972; c=relaxed/simple; bh=+wOG4qSFrgPQH/i7tE6iWyJ6XFGQlz0rsWZMNLfE29k=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=CQu894JXJzKbg3IwAwJ3fd6nWF6lQpeval903+kkgdsqRXBdyOewBQSXiXFSA96lMDL9sVg3hsEboP2EJ1rZeJohLecFjw1vcb9taVF/VjBlICDjrv1cvhlUv5eF5uqNeJop8YJBSFEyFeaNskZrRdiW7zU4xfoFVDV30EOFDYk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GxXT2RsZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GxXT2RsZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 97C78C116D0; Tue, 24 Feb 2026 06:52:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771915972; bh=+wOG4qSFrgPQH/i7tE6iWyJ6XFGQlz0rsWZMNLfE29k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GxXT2RsZidSTvkpJKtXv/7VE/DjQSPCqKgM7xvOVS5/+A5ybgFClHynEZan59s8nZ MxWaTwbtZD3y672MJPFWWRLpHCU2ZuAI8xIL2AlVJs+Ji7zHFhpAfsqCBzwXtjsePX Ro9imakn9z9oeNzmNrAq8whcxkWu2sbhGKa3GYx7SNlso47cxEZotmd6Trmpb+8uM8 6WMRvpwPc05TJgS+jHP/e+j7S8FaeHXvqaJwRx9saNS/zr0I37+0yjlWxCdgku9r2I YzkGyOoiQHboy4x3Kwkv2R31VRJJ8wqo73I3fv1ZL9pe0f6rS15yPzNz2LLY2AwlHH zcE94O7LBib7g== From: "Masami Hiramatsu (Google)" To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH v4 2/3] ring-buffer: Handle RB_MISSED_* flags on commit field correctly Date: Tue, 24 Feb 2026 15:52:50 +0900 Message-ID: <177191596996.435720.7165906136619645392.stgit@mhiramat.tok.corp.google.com> X-Mailer: git-send-email 2.53.0.371.g1d285c8824-goog In-Reply-To: <177191595057.435720.10116014529518464418.stgit@mhiramat.tok.corp.google.com> References: <177191595057.435720.10116014529518464418.stgit@mhiramat.tok.corp.google.com> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) Since the MSBs of rb_data_page::commit are used for storing RB_MISSED_EVENTS and RB_MISSED_STORED, we need to mask out those bits when it is used for finding the size of data pages. Fixes: 5f3b6e839f3c ("ring-buffer: Validate boot range memory events") Fixes: 5b7be9c709e1 ("ring-buffer: Add test to validate the time stamp delt= as") Cc: stable@vger.kernel.org Signed-off-by: Masami Hiramatsu (Google) --- Changes in v4: - Fix to move rb_commit_index() after ring_buffer_per_cpu definition. --- kernel/trace/ring_buffer.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3eb124c93d72..67bc652ba02a 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -395,6 +395,12 @@ static __always_inline unsigned int rb_page_commit(str= uct buffer_page *bpage) return local_read(&bpage->page->commit); } =20 +/* Size is determined by what has been committed */ +static __always_inline unsigned rb_page_size(struct buffer_page *bpage) +{ + return rb_page_commit(bpage) & ~RB_MISSED_MASK; +} + static void free_buffer_page(struct buffer_page *bpage) { /* Range pages are not to be freed */ @@ -614,6 +620,12 @@ struct ring_buffer_iter { int missed_events; }; =20 +static __always_inline unsigned +rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer) +{ + return rb_page_commit(cpu_buffer->commit_page); +} + int ring_buffer_print_page_header(struct trace_buffer *buffer, struct trac= e_seq *s) { struct buffer_data_page field; @@ -1907,7 +1919,7 @@ static int rb_validate_buffer(struct buffer_data_page= *dpage, int cpu) u64 delta; int tail; =20 - tail =3D local_read(&dpage->commit); + tail =3D local_read(&dpage->commit) & ~RB_MISSED_MASK; return rb_read_data_buffer(dpage, tail, cpu, &ts, &delta); } =20 @@ -1934,7 +1946,7 @@ static void rb_meta_validate_events(struct ring_buffe= r_per_cpu *cpu_buffer) goto invalid; } entries +=3D ret; - entry_bytes +=3D local_read(&cpu_buffer->reader_page->page->commit); + entry_bytes +=3D rb_page_size(cpu_buffer->reader_page); local_set(&cpu_buffer->reader_page->entries, ret); =20 ts =3D head_page->page->time_stamp; @@ -2054,7 +2066,7 @@ static void rb_meta_validate_events(struct ring_buffe= r_per_cpu *cpu_buffer) local_inc(&cpu_buffer->pages_touched); =20 entries +=3D ret; - entry_bytes +=3D local_read(&head_page->page->commit); + entry_bytes +=3D rb_page_size(head_page); local_set(&cpu_buffer->head_page->entries, ret); =20 if (head_page =3D=3D cpu_buffer->commit_page) @@ -3257,18 +3269,6 @@ rb_iter_head_event(struct ring_buffer_iter *iter) return NULL; } =20 -/* Size is determined by what has been committed */ -static __always_inline unsigned rb_page_size(struct buffer_page *bpage) -{ - return rb_page_commit(bpage) & ~RB_MISSED_MASK; -} - -static __always_inline unsigned -rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer) -{ - return rb_page_commit(cpu_buffer->commit_page); -} - static __always_inline unsigned rb_event_index(struct ring_buffer_per_cpu *cpu_buffer, struct ring_buffer_= event *event) { @@ -4433,7 +4433,7 @@ static void check_buffer(struct ring_buffer_per_cpu *= cpu_buffer, =20 if (tail =3D=3D CHECK_FULL_PAGE) { full =3D true; - tail =3D local_read(&bpage->commit); + tail =3D local_read(&bpage->commit) & ~RB_MISSED_MASK; } else if (info->add_timestamp & (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE)) { /* Ignore events with absolute time stamps */ From nobody Fri Apr 17 03:11:59 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3E755304BB8; Tue, 24 Feb 2026 06:53:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771915980; cv=none; b=nsy484Dc6tCpzzuAOUcFm8NReClv14FDYk0rlqzrSG0u3HWFkC4vsu1MtIiCgxS9qnCqYM2MmC0qJirpO5P9laR3ZGc/IKw5yPlMXiVUsh7zFB37/rdKXOx42uAvL7N0INWljoWpmvmBv9QFFl4AkiTNa08IH7XpS30U34xCONs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771915980; c=relaxed/simple; bh=Qf0TU7ksxuW8tRJJFNoCuCSkFLx0TOuA2b8MEfyqkSQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; 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charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Masami Hiramatsu (Google) Skip invalid sub-buffers when validating the persistent ring buffer instead of discarding the entire ring buffer. Also, mark there are missed events on the discarded buffer. If the cache data in memory fails to be synchronized during a reboot, the persistent ring buffer may become partially corrupted, but other sub-buffers may still contain readable event data. Only discard the subbuffersa that ar found to be corrupted. Signed-off-by: Masami Hiramatsu (Google) --- Changes in v3: - Record missed data event on commit. --- kernel/trace/ring_buffer.c | 21 +++++++++++---------- 1 file changed, 11 insertions(+), 10 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 67bc652ba02a..72f82e2e6740 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2058,17 +2058,18 @@ static void rb_meta_validate_events(struct ring_buf= fer_per_cpu *cpu_buffer) if (ret < 0) { pr_info("Ring buffer meta [%d] invalid buffer page\n", cpu_buffer->cpu); - goto invalid; - } - - /* If the buffer has content, update pages_touched */ - if (ret) - local_inc(&cpu_buffer->pages_touched); - - entries +=3D ret; - entry_bytes +=3D rb_page_size(head_page); - local_set(&cpu_buffer->head_page->entries, ret); + /* Instead of discard whole ring buffer, discard only this sub-buffer. = */ + local_set(&head_page->entries, 0); + local_set(&head_page->page->commit, RB_MISSED_EVENTS); + } else { + /* If the buffer has content, update pages_touched */ + if (ret) + local_inc(&cpu_buffer->pages_touched); =20 + entries +=3D ret; + entry_bytes +=3D rb_page_size(head_page); + local_set(&cpu_buffer->head_page->entries, ret); + } if (head_page =3D=3D cpu_buffer->commit_page) break; }