[v2,1/2] trace-cmd: Fix crash when trace-cmd is executed with args "profile -F sleep 1"
diff mbox series

Message ID 20190605111937.17894-1-tstoyanov@vmware.com
State Superseded
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Series
  • [v2,1/2] trace-cmd: Fix crash when trace-cmd is executed with args "profile -F sleep 1"
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Commit Message

Tzvetomir Stoyanov June 5, 2019, 11:19 a.m. UTC
A fix for https://bugzilla.kernel.org/show_bug.cgi?id=203411
When trace-cmd is running in "profile" mode, trace files are not generated.
Instead, pipes are used to collect trace data from recorder threads. Some
internal functions, originally designed for working with files, are reused
in pipes use case:
 init_cpu()
 allocate_page()
 get_next_page()
There was an undesired behaviour in those functions, when working with pipes,
which causes the segmentation fault, described in the bug report.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
---
 lib/trace-cmd/trace-input.c | 45 +++++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 12 deletions(-)

Comments

Steven Rostedt June 18, 2019, 4:20 p.m. UTC | #1
On Wed,  5 Jun 2019 14:19:36 +0300
Tzvetomir Stoyanov <tstoyanov@vmware.com> wrote:

> @@ -973,6 +984,17 @@ static void __free_page(struct tracecmd_input *handle, struct page *page)
>  	cpu_data->page_cnt--;
>  
>  	free(page);
> +
> +	for (index = cpu_data->nr_pages - 1; index > 0; index--)
> +		if (cpu_data->pages[index])
> +			break;
> +	if (index < (cpu_data->nr_pages - 1)) {
> +		pages = realloc(cpu_data->pages, (index + 1) * sizeof(*cpu_data->pages));
> +		if (!pages)
> +			return;
> +		cpu_data->pages = pages;
> +		cpu_data->nr_pages = index + 1;
> +	}
>  }
>  

Heads up. Johannes found a regression that this code above causes
reading a 1.7G file where the above code makes it go from reading it in
5 seconds, to over 2 minutes!

I bisected it down to this commit (saw a small, but not so drastic
performance issue it my tests). I asked Johannes to revert the commit,
and he said that it removed the regression.

He said he'll report this in the Bugzilla, but we should be looking at
changing the realloc() logic.

-- Steve
Johannes Berg June 18, 2019, 5:54 p.m. UTC | #2
On Tue, 2019-06-18 at 12:20 -0400, Steven Rostedt wrote:

> Heads up. Johannes found a regression that this code above causes
> reading a 1.7G file where the above code makes it go from reading it in
> 5 seconds, to over 2 minutes!

Actually, I didn't even let it finish ... It was something like 4.5
seconds to not finishing in 4.5 minutes, then I gave up. My prior
version was commit 1ad32c24746.

The file is 1.7G, but that's perhaps not the interesting part? A little
under 620k events - by my standards, that's a small file :-)

> I bisected it down to this commit (saw a small, but not so drastic
> performance issue it my tests). I asked Johannes to revert the commit,
> and he said that it removed the regression.

With that reverted I actually see ~2 seconds now, which is 2x faster
than before :-)

> He said he'll report this in the Bugzilla, but we should be looking at
> changing the realloc() logic.

https://bugzilla.kernel.org/show_bug.cgi?id=203927

johannes

Patch
diff mbox series

diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index ba20ef1..264e3c3 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -28,8 +28,6 @@ 
 /* for debugging read instead of mmap */
 static int force_read = 0;
 
-#define PAGE_STOPPER		((struct page *)-1L)
-
 struct page_map {
 	struct list_head	list;
 	off64_t			offset;
@@ -65,6 +63,7 @@  struct cpu_data {
 	struct tep_record	*next;
 	struct page		*page;
 	struct kbuffer		*kbuf;
+	int			nr_pages;
 	int			page_cnt;
 	int			cpu;
 	int			pipe_fd;
@@ -146,16 +145,17 @@  static void add_record(struct page *page, struct tep_record *record)
 	record->prev = NULL;
 	page->records = record;
 }
-static const char *show_records(struct page **pages)
+static const char *show_records(struct page **pages, int nr_pages)
 {
 	static char buf[BUFSIZ + 1];
 	struct tep_record *record;
 	struct page *page;
 	int len;
+	int i;
 
 	memset(buf, 0, sizeof(buf));
 	len = 0;
-	for (i = 0; pages[i] != PAGE_STOPPER; i--) {
+	for (i = 0; i < nr_pages; i++) {
 		page = pages[i];
 		if (!page)
 			continue;
@@ -172,7 +172,7 @@  static const char *show_records(struct page **pages)
 #else
 static inline void remove_record(struct page *page, struct tep_record *record) {}
 static inline void add_record(struct page *page, struct tep_record *record) {}
-static const char *show_records(struct page **pages)
+static const char *show_records(struct page **pages, int nr_pages)
 {
 	return "";
 }
@@ -919,10 +919,20 @@  static struct page *allocate_page(struct tracecmd_input *handle,
 				  int cpu, off64_t offset)
 {
 	struct cpu_data *cpu_data = &handle->cpu_data[cpu];
+	struct page **pages;
 	struct page *page;
 	int index;
 
 	index = (offset - cpu_data->file_offset) / handle->page_size;
+	if (index >= cpu_data->nr_pages) {
+		pages = realloc(cpu_data->pages, (index + 1) * sizeof(*cpu_data->pages));
+		if (!pages)
+			return NULL;
+		memset(pages + cpu_data->nr_pages, 0,
+		       (index + 1 - cpu_data->nr_pages) * sizeof(*cpu_data->pages));
+		cpu_data->pages = pages;
+		cpu_data->nr_pages = index + 1;
+	}
 	if (cpu_data->pages[index]) {
 		cpu_data->pages[index]->ref_count++;
 		return cpu_data->pages[index];
@@ -954,6 +964,7 @@  static struct page *allocate_page(struct tracecmd_input *handle,
 static void __free_page(struct tracecmd_input *handle, struct page *page)
 {
 	struct cpu_data *cpu_data = &handle->cpu_data[page->cpu];
+	struct page **pages;
 	int index;
 
 	if (!page->ref_count)
@@ -973,6 +984,17 @@  static void __free_page(struct tracecmd_input *handle, struct page *page)
 	cpu_data->page_cnt--;
 
 	free(page);
+
+	for (index = cpu_data->nr_pages - 1; index > 0; index--)
+		if (cpu_data->pages[index])
+			break;
+	if (index < (cpu_data->nr_pages - 1)) {
+		pages = realloc(cpu_data->pages, (index + 1) * sizeof(*cpu_data->pages));
+		if (!pages)
+			return;
+		cpu_data->pages = pages;
+		cpu_data->nr_pages = index + 1;
+	}
 }
 
 static void free_page(struct tracecmd_input *handle, int cpu)
@@ -2026,7 +2048,6 @@  tracecmd_read_prev(struct tracecmd_input *handle, struct tep_record *record)
 static int init_cpu(struct tracecmd_input *handle, int cpu)
 {
 	struct cpu_data *cpu_data = &handle->cpu_data[cpu];
-	int num_pages;
 	int i;
 
 	cpu_data->offset = cpu_data->file_offset;
@@ -2040,14 +2061,13 @@  static int init_cpu(struct tracecmd_input *handle, int cpu)
 		return 0;
 	}
 
-	num_pages = (cpu_data->size + handle->page_size - 1) / handle->page_size;
-	cpu_data->pages = calloc(num_pages + 1, sizeof(*cpu_data->pages));
+	cpu_data->nr_pages = (cpu_data->size + handle->page_size - 1) / handle->page_size;
+	if (!cpu_data->nr_pages)
+		cpu_data->nr_pages = 1;
+	cpu_data->pages = calloc(cpu_data->nr_pages, sizeof(*cpu_data->pages));
 	if (!cpu_data->pages)
 		return -1;
 
-	/* Add stopper */
-	cpu_data->pages[num_pages] = PAGE_STOPPER;
-
 	if (handle->use_pipe) {
 		/* Just make a page, it will be nuked later */
 		cpu_data->page = malloc(sizeof(*cpu_data->page));
@@ -2793,7 +2813,8 @@  void tracecmd_close(struct tracecmd_input *handle)
 			if (handle->cpu_data[cpu].page_cnt)
 				warning("%d pages still allocated on cpu %d%s",
 					handle->cpu_data[cpu].page_cnt,
-					cpu, show_records(handle->cpu_data[cpu].pages));
+					cpu, show_records(handle->cpu_data[cpu].pages,
+							  handle->cpu_data[cpu].nr_pages));
 			free(handle->cpu_data[cpu].pages);
 		}
 	}