The read optimization with buffer ustream in the logread caused the logger to
hung randomly, more often under high load and when logged messages are large.
To reproduce 100% compile and run:
#include <syslog.h>
#include <stdlib.h>
#include <string.h>
#define BUF_SIZE 8192
int i;
static char msg_buf[BUF_SIZE];
int main(int argc, char* argv[])
{
setlogmask(LOG_UPTO(LOG_NOTICE));
openlog(argv[0], LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL1);
syslog(LOG_NOTICE, "Program started by User %d", getuid());
syslog(LOG_INFO, "A tree falls in a forest");
memset(msg_buf, 'A', BUF_SIZE - 1);
msg_buf[BUF_SIZE-1] = '\0';
for (i=0; i < 10; ++i) syslog(LOG_NOTICE, msg_buf);
syslog(LOG_NOTICE, "After");
closelog();
exit(0);
}
The line "After" will not show up in the log and all subsequent log messages
are blocked.
Patch below against ubox master branch at
https://git.openwrt.org/project/ubox.git fixes the problem, keeping buffers
trickery as fast patch for short messages.
--- log/logread.c.orig 2017-10-19 16:31:04.033719240 +0100
+++ log/logread.c 2017-10-19 16:44:49.203118281 +0100
@@ -223,18 +223,34 @@
{
while (true) {
struct blob_attr *a;
- int len, cur_len;
+ int len, full_blob_len, read_pending_len, read;
+ char* buf;
a = (void*) ustream_get_read_buf(s, &len);
if (len < sizeof(*a))
break;
- cur_len = blob_len(a) + sizeof(*a);
- if (len < cur_len)
- break;
-
- log_notify(a);
- ustream_consume(s, cur_len);
+ full_blob_len = blob_raw_len(a);
+ if (len < full_blob_len) {
+ read_pending_len = ustream_pending_data(s, false);
+ if (read_pending_len < full_blob_len)
+ break;
+ buf = malloc(full_blob_len);
+ if (buf) {
+ read = 0;
+ do {
+ read += ustream_read(s, buf + read,
full_blob_len - read);
+ } while (read < full_blob_len);
+ log_notify((struct blob_attr*)buf);
+ free(buf);
+ } else {
+ fprintf(stderr, "Malloc failed\n");
+ break;
+ }
+ } else {
+ log_notify(a);
+ ustream_consume(s, full_blob_len);
+ }
}
if (!log_follow)
uloop_end();
@@ -245,6 +261,7 @@
static struct ustream_fd test_fd;
test_fd.stream.notify_read = logread_fd_data_cb;
+ test_fd.stream.r.max_buffers = -1;
ustream_fd_init(&test_fd, fd);
}
Maksym Ruchko
mruc...@advantech-bb.com
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