On Wed, Dec 16, 2020 at 06:34:05PM +0100, Martin Wilck wrote:
> On Fri, 2020-10-16 at 12:44 +0200, mwilck@xxxxxxxx wrote:
> > From: Martin Wilck <mwilck@xxxxxxxx>
> >
> > There were two leaks in check_path_valid(): if path status was
> > successfully determined before calling store_pathvec(), free_path()
> > wasn't called. Also, if an error exit occured, neither cleanup
> > function was called.
> >
> > This patch fixes both, at the cost of using "static" for the pp and
> > pathvec variables.
>
> Looking at this again after 2 months, I think the on_exit() part of
> this patch is wrong. First, we can't use on_exit() on every platform,
> as e.g. musl libc doesn't have it. To replace this by the more portable
> atexit(), we'd need to declare the two variables "pp" and "pathvec"
> with file scope, which is very ugly. But more importantly, using static
> variables here causes check_path_valid() to be non-reentrant. While it
> doesn't have to be, it's still a coding pattern we haven't been using
> anywhere else, just to avoid a "memory leak" for an irregular exit,
> which isn't a real memory leak, actually.
A while ago, we had a conversation where we talked about not adding too
much complexity to deal with issues on shutdown, that will just go away
when multipathd stops. I still think that we shouldn't worry too much
about making sure we always free everything when it will automatically
get freed by the system anyway.
-Ben
>
> One day we should remove the exit() calls somewhere deep down in our
> libraries, and deal with the respective errors cleanly.
>
> @lixiaokeng, I hope this is ok for you, as you brought the issue up
> originally ("[QUESTION] memory leak in main (multipath)").
>
> Regards
> Martin
>
> >
> > Reviewed-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> > Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> > ---
> > multipath/main.c | 55 +++++++++++++++++++++++++++++++++++++---------
> > --
> > 1 file changed, 43 insertions(+), 12 deletions(-)
> >
> > diff --git a/multipath/main.c b/multipath/main.c
> > index 049a36f..9974993 100644
> > --- a/multipath/main.c
> > +++ b/multipath/main.c
> > @@ -93,7 +93,7 @@ void rcu_register_thread_memb(void) {}
> > void rcu_unregister_thread_memb(void) {}
> >
> > static int
> > -filter_pathvec (vector pathvec, char * refwwid)
> > +filter_pathvec (vector pathvec, const char *refwwid)
> > {
> > int i;
> > struct path * pp;
> > @@ -592,12 +592,37 @@ out:
> > return r;
> > }
> >
> > +static void cleanup_pathvec(__attribute__((unused)) int dummy, void
> > *arg)
> > +{
> > + vector *ppv = arg;
> > +
> > + if (ppv && *ppv) {
> > + free_pathvec(*ppv, FREE_PATHS);
> > + *ppv = NULL;
> > + }
> > +}
> > +
> > +static void cleanup_path(__attribute__((unused)) int dummy, void
> > *arg)
> > +{
> > + struct path **ppp = arg;
> > +
> > + if (ppp && *ppp) {
> > + free_path(*ppp);
> > + *ppp = NULL;
> > + }
> > +}
> > +
> > static int
> > check_path_valid(const char *name, struct config *conf, bool
> > is_uevent)
> > {
> > int fd, r = PATH_IS_ERROR;
> > - struct path *pp = NULL;
> > - vector pathvec = NULL;
> > + static struct path *pp = NULL;
> > + static vector pathvec = NULL;
> > + const char *wwid;
> > +
> > + /* register these as exit handlers in case we exit irregularly
> > */
> > + on_exit(cleanup_path, &pp);
> > + on_exit(cleanup_pathvec, &pathvec);
> >
> > pp = alloc_path();
> > if (!pp)
> > @@ -667,13 +692,17 @@ check_path_valid(const char *name, struct
> > config *conf, bool is_uevent)
> > if (store_path(pathvec, pp) != 0) {
> > free_path(pp);
> > goto fail;
> > + } else {
> > + /* make sure path isn't freed twice */
> > + wwid = pp->wwid;
> > + pp = NULL;
> > }
> >
> > /* For find_multipaths = SMART, if there is more than one path
> > * matching the refwwid, then the path is valid */
> > if (path_discovery(pathvec, DI_SYSFS | DI_WWID) < 0)
> > goto fail;
> > - filter_pathvec(pathvec, pp->wwid);
> > + filter_pathvec(pathvec, wwid);
> > if (VECTOR_SIZE(pathvec) > 1)
> > r = PATH_IS_VALID;
> > else
> > @@ -681,21 +710,23 @@ check_path_valid(const char *name, struct
> > config *conf, bool is_uevent)
> >
> > out:
> > r = print_cmd_valid(r, pathvec, conf);
> > - free_pathvec(pathvec, FREE_PATHS);
> > /*
> > * multipath -u must exit with status 0, otherwise udev won't
> > * import its output.
> > */
> > if (!is_uevent && r == PATH_IS_NOT_VALID)
> > - return RTVL_FAIL;
> > - return RTVL_OK;
> > + r = RTVL_FAIL;
> > + else
> > + r = RTVL_OK;
> > + goto cleanup;
> >
> > fail:
> > - if (pathvec)
> > - free_pathvec(pathvec, FREE_PATHS);
> > - else
> > - free_path(pp);
> > - return RTVL_FAIL;
> > + r = RTVL_FAIL;
> > +
> > +cleanup:
> > + cleanup_path(0, &pp);
> > + cleanup_pathvec(0, &pathvec);
> > + return r;
> > }
> >
> > static int
>
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