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mdev: if a "future" mdev.seq is seen, do not overwrite it with ours

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This was seen to happen if two mdevs are run in parallel,
mdev.seq is empty, and the "newer" one manages to write it first.

function                                             old     new   delta
mdev_main                                           1366    1388     +22
atoll                                                  -      20     +20

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2015-04-19 18:55:12 +02:00
parent bd77e9d609
commit ad795510d9
1 changed files with 22 additions and 7 deletions
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29
util-linux/mdev.c
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@ -947,7 +947,7 @@ static void open_mdev_log(const char *seq, unsigned my_pid)
* Active mdev pokes us with SIGCHLD to check the new file.
*/
static int
wait_for_seqfile(const char *seq)
wait_for_seqfile(unsigned expected_seq)
{
/* We time out after 2 sec */
static const struct timespec ts = { 0, 32*1000*1000 };
@ -962,12 +962,14 @@ wait_for_seqfile(const char *seq)
for (;;) {
int seqlen;
char seqbuf[sizeof(int)*3 + 2];
char seqbuf[sizeof(long)*3 + 2];
unsigned seqbufnum;
if (seq_fd < 0) {
seq_fd = open("mdev.seq", O_RDWR);
if (seq_fd < 0)
break;
close_on_exec_on(seq_fd);
}
seqlen = pread(seq_fd, seqbuf, sizeof(seqbuf) - 1, 0);
if (seqlen < 0) {
@ -978,17 +980,25 @@ wait_for_seqfile(const char *seq)
seqbuf[seqlen] = '\0';
if (seqbuf[0] == '\n' || seqbuf[0] == '\0') {
/* seed file: write out seq ASAP */
xwrite_str(seq_fd, seq);
xwrite_str(seq_fd, utoa(expected_seq));
xlseek(seq_fd, 0, SEEK_SET);
dbg2("first seq written");
break;
}
if (strcmp(seq, seqbuf) == 0) {
seqbufnum = atoll(seqbuf);
if (seqbufnum == expected_seq) {
/* correct idx */
break;
}
if (seqbufnum > expected_seq) {
/* a later mdev runs already (this was seen by users to happen) */
/* do not overwrite seqfile on exit */
close(seq_fd);
seq_fd = -1;
break;
}
if (do_once) {
dbg2("%s mdev.seq='%s', need '%s'", curtime(), seqbuf, seq);
dbg2("%s mdev.seq='%s', need '%u'", curtime(), seqbuf, expected_seq);
do_once = 0;
}
if (sigtimedwait(&set_CHLD, NULL, &ts) >= 0) {
@ -1079,6 +1089,7 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
char *env_devname;
char *env_devpath;
unsigned my_pid;
unsigned seqnum = seqnum; /* for compiler */
int seq_fd;
smalluint op;
@ -1100,7 +1111,11 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
my_pid = getpid();
open_mdev_log(seq, my_pid);
seq_fd = seq ? wait_for_seqfile(seq) : -1;
seq_fd = -1;
if (seq) {
seqnum = atoll(seq);
seq_fd = wait_for_seqfile(seqnum);
}
dbg1("%s "
"ACTION:%s SUBSYSTEM:%s DEVNAME:%s DEVPATH:%s"
@ -1128,7 +1143,7 @@ int mdev_main(int argc UNUSED_PARAM, char **argv)
dbg1("%s exiting", curtime());
if (seq_fd >= 0) {
xwrite_str(seq_fd, utoa(xatou(seq) + 1));
xwrite_str(seq_fd, utoa(seqnum + 1));
signal_mdevs(my_pid);
}
}