From b3230c8b44da5838cf396942d5c1ab19f8e8f720 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 21 May 2010 11:55:21 -0400 Subject: ring-buffer: Reset "real_end" when page is filled The code to store the "lost events" requires knowing the real end of the page. Since the 'commit' includes the padding at the end of a page a "real_end" variable was used to keep track of the end not including the padding. If events were lost, the reader can place the count of events in the padded area if there is enough room. The bug this patch fixes is that when we fill the page we do not reset the real_end variable, and if the writer had wrapped a few times, the real_end would be incorrect. This patch simply resets the real_end if the page was filled. Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'kernel') diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 7f6059c5aa94..b0702ff78218 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1768,6 +1768,14 @@ rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer, * must fill the old tail_page with padding. */ if (tail >= BUF_PAGE_SIZE) { + /* + * If the page was filled, then we still need + * to update the real_end. Reset it to zero + * and the reader will ignore it. + */ + if (tail == BUF_PAGE_SIZE) + tail_page->real_end = 0; + local_sub(length, &tail_page->write); return; } -- cgit v1.2.2 From 2711ca237a084286ea1c2dcf82ab2aadab23a00d Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 21 May 2010 13:32:26 -0400 Subject: ring-buffer: Move zeroing out excess in page to ring buffer code Currently the trace splice code zeros out the excess bytes in the page before sending it off to userspace. This is to make sure userspace is not getting anything it should not be when reading the pages, because the excess data was never initialized to zero before writing (for perfomance reasons). But the splice code has no business in doing this work, it should be done by the ring buffer. With the latest changes for recording lost events, the splice code gets it wrong anyway. Move the zeroing out of excess bytes into the ring buffer code. Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 11 +++++++++-- kernel/trace/trace.c | 6 ------ 2 files changed, 9 insertions(+), 8 deletions(-) (limited to 'kernel') diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index b0702ff78218..1da7b6ea8b85 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -3902,12 +3902,12 @@ int ring_buffer_read_page(struct ring_buffer *buffer, ret = read; cpu_buffer->lost_events = 0; + + commit = local_read(&bpage->commit); /* * Set a flag in the commit field if we lost events */ if (missed_events) { - commit = local_read(&bpage->commit); - /* If there is room at the end of the page to save the * missed events, then record it there. */ @@ -3915,10 +3915,17 @@ int ring_buffer_read_page(struct ring_buffer *buffer, memcpy(&bpage->data[commit], &missed_events, sizeof(missed_events)); local_add(RB_MISSED_STORED, &bpage->commit); + commit += sizeof(missed_events); } local_add(RB_MISSED_EVENTS, &bpage->commit); } + /* + * This page may be off to user land. Zero it out here. + */ + if (commit < BUF_PAGE_SIZE) + memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit); + out_unlock: spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index ba0ec81158b2..95d0b1a28f93 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3661,7 +3661,6 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, size_t count, loff_t *ppos) { struct ftrace_buffer_info *info = filp->private_data; - unsigned int pos; ssize_t ret; size_t size; @@ -3688,11 +3687,6 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, if (ret < 0) return 0; - pos = ring_buffer_page_len(info->spare); - - if (pos < PAGE_SIZE) - memset(info->spare + pos, 0, PAGE_SIZE - pos); - read: size = PAGE_SIZE - info->read; if (size > count) -- cgit v1.2.2