On Tue, 2018-10-09 at 18:02 -0500, Benjamin Marzinski wrote:
> The code previously was timing out mode if ct->thread was 0 but
> ct->running wasn't. This combination never happens. The idea was to
> timeout if for some reason the path checker tried to cancel the
> thread,
> but it didn't die. The correct thing to check for this is ct-
> >holders.
> ct->holders will always be at least one when libcheck_check() is
> called,
> since libcheck_free() won't get called until the device is no longer
> being checked. So, if ct->holders is 2, that means that the tur
> thread
> is has not shut down yet.
>
> Also, instead of timing out, the tur checker will switch to
> synchronous
> mode. The chance of this code path happening is very low. I simply
> exists because the old thread must not interfere with a new thread
> starting up. But if something does go very wrong, and a thread does
> get
> stuck, this solution will keep the checker from just ignoring the
> device
> forever.
Well, the previous tur thread hanging means that future attempts might
hang as well, in which case the synchronous approach would block _all_
path checkers. Wouldn't the following reasoning apply here?
commit 05cbea354172be5507ac83c98bbac8e02aa8cf3c
Author: Hannes Reinecke <hare@xxxxxxx>
Date: Fri Dec 13 13:12:42 2013 +0100
multipath: do not call tur in sync mode if pthread_cancel fails
When pthread_cancel fails the thread is stuck, most likely
during I/O submission. So it would be pointless to call the
tur checker in sync mode here, as this would be stuck, too.
I argued before that the current PATH_TIMEOUT return code is wrong, but
I think it's better than falling back to synchronous mode.
I'm fine with this patch if the return PATH_TIMEOUT remains for now,
and we vow to fix this for good soon.
> s
> Signed-off-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> ---
> libmultipath/checkers/tur.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/libmultipath/checkers/tur.c
> b/libmultipath/checkers/tur.c
> index bf8486d..3c5e236 100644
> --- a/libmultipath/checkers/tur.c
> +++ b/libmultipath/checkers/tur.c
> @@ -355,12 +355,13 @@ int libcheck_check(struct checker * c)
> }
> pthread_mutex_unlock(&ct->lock);
> } else {
> - if (uatomic_read(&ct->running) != 0) {
> - /* pthread cancel failed. continue in sync mode
> */
> + if (uatomic_read(&ct->holders) > 1) {
> + /* The thread has been cancelled but hasn't
> + * quilt. Fail back to synchronous mode */
Typo.
> pthread_mutex_unlock(&ct->lock);
> - condlog(3, "%s: tur thread not responding",
> + condlog(3, "%s: tur checker failing back to
> sync",
> tur_devt(devt, sizeof(devt), ct));
> - return PATH_TIMEOUT;
> + return tur_check(c->fd, c->timeout,
> copy_msg_to_checker, c);
> }
> /* Start new TUR checker */
> ct->state = PATH_UNCHECKED;
Regards,
Martin
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