| Message ID | 1620775324-23984-4-git-send-email-bmarzins@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | christophe varoqui |
| Headers | show |
| Series | Memory issues found by coverity | expand |
On Tue, 2021-05-11 at 18:22 -0500, Benjamin Marzinski wrote: > When ev_remove_path() returns success, callers assume that the path > (and > possibly the map) has been removed. When ev_remove_path() returns > failure, callers assume that the path has not been removed. However, > the > path could be removed on both success or failure. This could cause > callers to dereference the path after it was removed. Change > ev_remove_path() to return success whenever the path is removed, even > if > the map was removed due to a failure when trying to reload it. Found by > coverity. > > Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com> This looks ok, but I'd like to discuss it in some more depth. We need to clarify the meaning of the return code of ev_remove_path(). We guarantee that, when ev_remove_path() returns, either the path is removed from internal data structures and kernel maps, or INIT_REMOVED is set. We can't guarantee whether the path a) is not referenced any more by any kernel map, b) was actually removed from pathvec and other data structures in multipathd. We have to agree on whether it means a) or b) if we can't make these two cases equivalent. Assuming multipathd has correct information about the kernel mappings, the only difference between a) and b) is the unlikely failure in setup_multipath(), where a) is true and b) is not (because sync_map_state() won't be called). Your patch assumes the semantics of a), which is correct AFAICS, but should be more clearly documented. Actually, I think we can fix the discrepancy between a) and b) - if domap() was successful, we should be able to orphan the path, even if update_multipath_strings() failed for some reason. IMO we should consequently change the retval for the cases where ev_remove_path() returns without deleting the path for a non-"failure" case (wait_for_udev and !need_do_map). Thoughts? Whatever we decide wrt the semantics of the return code, we should document it clearly in comments at the function header. Here's a quick review of callers: - cli_add_path(): AFAICS this needs b) semantics. We shouldn't set up a new path unless it had been successfully removed internally. - cli_del_path(): needs a) semantics. - handle_path_wwid_change(): needs a). - uev_add_path(): needs a). - uev_remove_path(): the return code of ev_remove_path doesn't matter much here. This is the only caller that sets need_do_map = false. - uev_update_path(): we currently don't look at the return code. uev_add_path() will make another attempt at removing the path if necessary. Regards Martin P.S.: The remaining failure cases in ev_remove_path() are the failures in update_mpp_paths() and setup_map(). The former can only fail with ENOMEM, afaics. The latter, likewise, or if the map is fundamentally misconfigured (which to me means that a previous call to setup_map() would have failed as well). I'm wondering why we remove the entire map in these failure cases. This goes back all the way to 45eb316 ("[multipathd] DM configuration final cut") from 2005. It's true that both failures are pretty much fatal, but why is removing the map the answer here? However, this goes beyond the purpose of your patch. *If* we remove the map, returning 0 is correct for either a) or b). P.S. 2: I wonder if the logic in uev_update_path() is correct. Rather than calling uev_add_path() after rescan_path() directly, I think we should rather wait for another uevent (and possibly trigger another "add" event, I don't think "rescan" automatically generates one). > --- > multipathd/main.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/multipathd/main.c b/multipathd/main.c > index 6090434c..4bdf14bd 100644 > --- a/multipathd/main.c > +++ b/multipathd/main.c > @@ -1284,7 +1284,7 @@ ev_remove_path (struct path *pp, struct vectors * > vecs, int need_do_map) > > strlcpy(devt, pp->dev_t, sizeof(devt)); > if (setup_multipath(vecs, mpp)) > - return 1; > + return 0; > /* > * Successful map reload without this path: > * sync_map_state() will free it. > @@ -1304,8 +1304,10 @@ out: > return retval; > > fail: > + condlog(0, "%s: error removing path. removing map %s", pp->dev, > + mpp->alias); > remove_map_and_stop_waiter(mpp, vecs); > - return 1; > + return 0; > } > > static int -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
On Wed, May 12, 2021 at 11:38:08AM +0000, Martin Wilck wrote: > On Tue, 2021-05-11 at 18:22 -0500, Benjamin Marzinski wrote: > > When ev_remove_path() returns success, callers assume that the path > > (and > > possibly the map) has been removed. When ev_remove_path() returns > > failure, callers assume that the path has not been removed. However, > > the > > path could be removed on both success or failure. This could cause > > callers to dereference the path after it was removed. Change > > ev_remove_path() to return success whenever the path is removed, even > > if > > the map was removed due to a failure when trying to reload it. Found by > > coverity. > > > > Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com> > > This looks ok, but I'd like to discuss it in some more depth. > > We need to clarify the meaning of the return code of ev_remove_path(). > We guarantee that, when ev_remove_path() returns, either the path is > removed from internal data structures and kernel maps, or INIT_REMOVED > is set. We can't guarantee whether the path > > a) is not referenced any more by any kernel map, > b) was actually removed from pathvec and other data structures in > multipathd. > > We have to agree on whether it means a) or b) if we can't make these > two cases equivalent. Assuming multipathd has correct information about > the kernel mappings, the only difference between a) and b) is the > unlikely failure in setup_multipath(), where a) is true and b) is not > (because sync_map_state() won't be called). Your patch assumes the > semantics of a), which is correct AFAICS, but should be more clearly > documented. Well, actually because of wait_for_udev and !need_do_map, a successful return can still leave the kernel maps and internal structures unchanged. It's just that callers have to assume that b is the case. > Actually, I think we can fix the discrepancy between a) and b) - if > domap() was successful, we should be able to orphan the path, even if > update_multipath_strings() failed for some reason. I'm pretty sure that this is already the case. This comment /* * Successful map reload without this path: * sync_map_state() will free it. */ is a lie. If setup_multipath() succeeds, the path will get removed by check_removed_paths() via: __setup_multipath -> update_path_strings -> sync_paths -> check_removed_paths If setup_multipath() fails, the path will get removed by remove_map_and_stop_waiter() via: __setup_multipath -> remove_map_and_stop_waiter -> remove_map -> orphan_paths So AFAICS, the only way for a path not to get removed is if you succeed with wait_for_udev or !need_do_map, or if you fail in domap. > IMO we should consequently change the retval for the cases where > ev_remove_path() returns without deleting the path for a non-"failure" > case (wait_for_udev and !need_do_map). So you think these should return failure? For need_do_map, I think we would want to distinguish between cases where everything worked correctly and we're just waiting to update the map, and cases where something went wrong. Since wait_for_udev can happen in more situations, it's a lot harder to say what the right answer is. For cli_add_path and uev_add_path, it seems like we want to know if the path was really removed. So returning failure there makes sense. For cli_del_path and uev_remove_path, it seems like we want to avoid spurious error messages when everything went alright and we're just waiting to update the map. So returning success makes sense there. Perhaps the answer is to return symbolic values, to describe what actually happened, rather than success or failure. They could either be bitmask values or we could have helper functions to help checking for multiple valid return values. > Thoughts? Whatever we decide wrt the semantics of the return code, we > should document it clearly in comments at the function header. > > Here's a quick review of callers: > > - cli_add_path(): AFAICS this needs b) semantics. We shouldn't set up > a new path unless it had been successfully removed internally. > - cli_del_path(): needs a) semantics. > - handle_path_wwid_change(): needs a). > - uev_add_path(): needs a). > - uev_remove_path(): the return code of ev_remove_path doesn't matter > much here. This is the only caller that sets need_do_map = false. > - uev_update_path(): we currently don't look at the return code. > uev_add_path() will make another attempt at removing the path if > necessary. > > Regards > Martin > > P.S.: The remaining failure cases in ev_remove_path() are the failures > in update_mpp_paths() and setup_map(). The former can only fail with > ENOMEM, afaics. The latter, likewise, or if the map is fundamentally > misconfigured (which to me means that a previous call to setup_map() > would have failed as well). I'm wondering why we remove the entire map > in these failure cases. This goes back all the way to 45eb316 > ("[multipathd] DM configuration final cut") from 2005. It's true that > both failures are pretty much fatal, but why is removing the map the > answer here? I don't think it has to be the answer. There are other cases where setup_map() fails and we don't automatically wipe the map. I did consider changing it when I was looking through ev_remove_path(), but I've never known this code to cause any issues, and as you mention, it isn't wrong to do so, just not really necessary AFAICS. > However, this goes beyond the purpose of your patch. *If* we remove the > map, returning 0 is correct for either a) or b). > > P.S. 2: I wonder if the logic in uev_update_path() is correct. Rather > than calling uev_add_path() after rescan_path() directly, I think we > should rather wait for another uevent (and possibly trigger another > "add" event, I don't think "rescan" automatically generates one). > Yep. You're correct. I'll fix that. -Ben > > > --- > > multipathd/main.c | 6 ++++-- > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/multipathd/main.c b/multipathd/main.c > > index 6090434c..4bdf14bd 100644 > > --- a/multipathd/main.c > > +++ b/multipathd/main.c > > @@ -1284,7 +1284,7 @@ ev_remove_path (struct path *pp, struct vectors * > > vecs, int need_do_map) > > > > strlcpy(devt, pp->dev_t, sizeof(devt)); > > if (setup_multipath(vecs, mpp)) > > - return 1; > > + return 0; > > /* > > * Successful map reload without this path: > > * sync_map_state() will free it. > > @@ -1304,8 +1304,10 @@ out: > > return retval; > > > > fail: > > + condlog(0, "%s: error removing path. removing map %s", pp->dev, > > + mpp->alias); > > remove_map_and_stop_waiter(mpp, vecs); > > - return 1; > > + return 0; > > } > > > > static int -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
On Wed, 2021-05-12 at 14:53 -0500, Benjamin Marzinski wrote: > On Wed, May 12, 2021 at 11:38:08AM +0000, Martin Wilck wrote: > > On Tue, 2021-05-11 at 18:22 -0500, Benjamin Marzinski wrote: > > > When ev_remove_path() returns success, callers assume that the > > > path > > > (and > > > possibly the map) has been removed. When ev_remove_path() > > > returns > > > failure, callers assume that the path has not been removed. > > > However, > > > the > > > path could be removed on both success or failure. This could > > > cause > > > callers to dereference the path after it was removed. Change > > > ev_remove_path() to return success whenever the path is removed, > > > even > > > if > > > the map was removed due to a failure when trying to reload it. > > > Found by > > > coverity. > > > > > > Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com> > > > > This looks ok, but I'd like to discuss it in some more depth. > > > > We need to clarify the meaning of the return code of > > ev_remove_path(). > > We guarantee that, when ev_remove_path() returns, either the path > > is > > removed from internal data structures and kernel maps, or > > INIT_REMOVED > > is set. We can't guarantee whether the path > > > > a) is not referenced any more by any kernel map, > > b) was actually removed from pathvec and other data structures in > > multipathd. > > > > We have to agree on whether it means a) or b) if we can't make > > these > > two cases equivalent. Assuming multipathd has correct information > > about > > the kernel mappings, the only difference between a) and b) is the > > unlikely failure in setup_multipath(), where a) is true and b) is > > not > > (because sync_map_state() won't be called). Your patch assumes the > > semantics of a), which is correct AFAICS, but should be more > > clearly > > documented. > > Well, actually because of wait_for_udev and !need_do_map, a > successful > return can still leave the kernel maps and internal structures > unchanged. It's just that callers have to assume that b is the case. > > > Actually, I think we can fix the discrepancy between a) and b) - if > > domap() was successful, we should be able to orphan the path, even > > if > > update_multipath_strings() failed for some reason. > > I'm pretty sure that this is already the case. This comment > > /* > * Successful map reload without this path: > * sync_map_state() will free it. > */ > > is a lie. Indeed, you are right. I wasn't deliberately lying though, just failing to understand my own code :-( We should fix these comments. > If setup_multipath() succeeds, the path will get removed by > check_removed_paths() via: > > __setup_multipath -> update_path_strings -> sync_paths -> > check_removed_paths > > If setup_multipath() fails, the path will get removed by > remove_map_and_stop_waiter() via: > > __setup_multipath -> remove_map_and_stop_waiter -> remove_map -> > orphan_paths > > So AFAICS, the only way for a path not to get removed is if you > succeed > with wait_for_udev or !need_do_map, or if you fail in domap. Agreed. Let's fix these comments. > > IMO we should consequently change the retval for the cases where > > ev_remove_path() returns without deleting the path for a non- > > "failure" > > case (wait_for_udev and !need_do_map). > > So you think these should return failure? What I meant is that the return code of the function doesn't need to be interpreted in terms of "success" or "failure". Rather as "path is now gone" or "path is still referenced somewhere", which doesn't map 1:1 to "success" and "failure", IMO. > For need_do_map, I think we > would want to distinguish between cases where everything worked > correctly and we're just waiting to update the map, and cases where > something went wrong. This one is actually trivial, because it's only set to false by uev_remove_path() if it's merging uevents. > Since wait_for_udev can happen in more situations, > it's a lot harder to say what the right answer is. For cli_add_path > and > uev_add_path, it seems like we want to know if the path was really > removed. So returning failure there makes sense. For cli_del_path > and > uev_remove_path, it seems like we want to avoid spurious error > messages > when everything went alright and we're just waiting to update the > map. > So returning success makes sense there. > > Perhaps the answer is to return symbolic values, to describe what > actually happened, rather than success or failure. This is what I meant. I didn't express myself clearly enough; I just thought that 0 doesn't have to mean "success". > They could either be > bitmask values or we could have helper functions to help checking > for multiple valid return values. I think the callers just need to know if the path is still referenced somewhere. Acting appropriately is then up to the caller. You just proved that my cases a) and b) are actually equivalent, which is nice. Perhaps we need to introduce another return code indicating that the entire map had been removed (e.g. failure in setup_multipath()). > > Thoughts? Whatever we decide wrt the semantics of the return code, > > we > > should document it clearly in comments at the function header. > > > > Here's a quick review of callers: > > > > - cli_add_path(): AFAICS this needs b) semantics. We shouldn't set > > up > > a new path unless it had been successfully removed internally. > > - cli_del_path(): needs a) semantics. > > - handle_path_wwid_change(): needs a). > > - uev_add_path(): needs a). > > - uev_remove_path(): the return code of ev_remove_path doesn't > > matter > > much here. This is the only caller that sets need_do_map = false. > > - uev_update_path(): we currently don't look at the return code. > > uev_add_path() will make another attempt at removing the path if > > necessary. > > > > Regards > > Martin > > > > P.S.: The remaining failure cases in ev_remove_path() are the > > failures > > in update_mpp_paths() and setup_map(). The former can only fail > > with > > ENOMEM, afaics. The latter, likewise, or if the map is > > fundamentally > > misconfigured (which to me means that a previous call to > > setup_map() > > would have failed as well). I'm wondering why we remove the entire > > map > > in these failure cases. This goes back all the way to 45eb316 > > ("[multipathd] DM configuration final cut") from 2005. It's true > > that > > both failures are pretty much fatal, but why is removing the map > > the > > answer here? > > I don't think it has to be the answer. There are other cases where > setup_map() fails and we don't automatically wipe the map. I did > consider changing it when I was looking through ev_remove_path(), but > I've never known this code to cause any issues, and as you mention, > it isn't wrong to do so, just not really necessary AFAICS. Let's take care of this another time. Regards, Martin > > > However, this goes beyond the purpose of your patch. *If* we remove > > the > > map, returning 0 is correct for either a) or b). > > > > P.S. 2: I wonder if the logic in uev_update_path() is correct. > > Rather > > than calling uev_add_path() after rescan_path() directly, I think > > we > > should rather wait for another uevent (and possibly trigger another > > "add" event, I don't think "rescan" automatically generates one). > > > > Yep. You're correct. I'll fix that. > > -Ben > > > > > > --- > > > multipathd/main.c | 6 ++++-- > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > diff --git a/multipathd/main.c b/multipathd/main.c > > > index 6090434c..4bdf14bd 100644 > > > --- a/multipathd/main.c > > > +++ b/multipathd/main.c > > > @@ -1284,7 +1284,7 @@ ev_remove_path (struct path *pp, struct > > > vectors * > > > vecs, int need_do_map) > > > > > > strlcpy(devt, pp->dev_t, sizeof(devt)); > > > if (setup_multipath(vecs, mpp)) > > > - return 1; > > > + return 0; > > > /* > > > * Successful map reload without this > > > path: > > > * sync_map_state() will free it. > > > @@ -1304,8 +1304,10 @@ out: > > > return retval; > > > > > > fail: > > > + condlog(0, "%s: error removing path. removing map %s", > > > pp->dev, > > > + mpp->alias); > > > remove_map_and_stop_waiter(mpp, vecs); > > > - return 1; > > > + return 0; > > > } > > > > > > static int > > -- > dm-devel mailing list > dm-devel@redhat.com > https://listman.redhat.com/mailman/listinfo/dm-devel > -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
On Wed, May 12, 2021 at 08:36:49PM +0000, Martin Wilck wrote: > On Wed, 2021-05-12 at 14:53 -0500, Benjamin Marzinski wrote: > > On Wed, May 12, 2021 at 11:38:08AM +0000, Martin Wilck wrote: > > > On Tue, 2021-05-11 at 18:22 -0500, Benjamin Marzinski wrote: > > So AFAICS, the only way for a path not to get removed is if you > > succeed > > with wait_for_udev or !need_do_map, or if you fail in domap. > > Agreed. Let's fix these comments. Yep. > > Since wait_for_udev can happen in more situations, > > it's a lot harder to say what the right answer is. For cli_add_path > > and > > uev_add_path, it seems like we want to know if the path was really > > removed. So returning failure there makes sense. For cli_del_path > > and > > uev_remove_path, it seems like we want to avoid spurious error > > messages > > when everything went alright and we're just waiting to update the > > map. > > So returning success makes sense there. > > > > Perhaps the answer is to return symbolic values, to describe what > > actually happened, rather than success or failure. > > This is what I meant. I didn't express myself clearly enough; I just > thought that 0 doesn't have to mean "success". > Sure. I'll add symbolic returns. > > I think the callers just need to know if the path is still referenced > somewhere. Acting appropriately is then up to the caller. You just > proved that my cases a) and b) are actually equivalent, which is nice. > Perhaps we need to introduce another return code indicating that the > entire map had been removed (e.g. failure in setup_multipath()). The more important return to me seems to be an indication of whether the remove has been delayed. For uev_remove_path(), you don't want to return failure just because the remove has been delayed. Otherwise there will be spurious error messages in the logs. cli_del_path is a little trickier. My biggest question with that is whether it would mess with people's scripts to add a reply message saying what happened. It seems like it should only fail if domap failed. But it would be nice to tell the user that the remove has been delayed, or that the map couldn't be reloaded and was removed as well. > > > However, this goes beyond the purpose of your patch. *If* we remove > > > the > > > map, returning 0 is correct for either a) or b). > > > > > > P.S. 2: I wonder if the logic in uev_update_path() is correct. > > > Rather > > > than calling uev_add_path() after rescan_path() directly, I think > > > we > > > should rather wait for another uevent (and possibly trigger another > > > "add" event, I don't think "rescan" automatically generates one). > > > > > > > Yep. You're correct. I'll fix that. Actually, I take it back. The code seems to work o.k. as is. The uev_update_path() code checks if get_uid() now returns a different value, instead of using get_vpd_sgio() like the recheck_wwid code does. This means that the uid_attribute must have already gotten updated when rescan_path() is called. So my real question is "is there any real benefit to calling rescan_path() at all here". This code seemed to be working correctly before we added it, except in the case where uid_attribute wasn't getting updated (which recheck_wwid now will hopefully catch). If there is a benefit, then we have to be careful to only call it once. Otherwise, we could get stuck in an endless loop where we trigger an add uevent, which in turn triggers another add uevent, and so on. -Ben > > -Ben > > > > > > > > > --- > > > > multipathd/main.c | 6 ++++-- > > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/multipathd/main.c b/multipathd/main.c > > > > index 6090434c..4bdf14bd 100644 > > > > --- a/multipathd/main.c > > > > +++ b/multipathd/main.c > > > > @@ -1284,7 +1284,7 @@ ev_remove_path (struct path *pp, struct > > > > vectors * > > > > vecs, int need_do_map) > > > > > > > > strlcpy(devt, pp->dev_t, sizeof(devt)); > > > > if (setup_multipath(vecs, mpp)) > > > > - return 1; > > > > + return 0; > > > > /* > > > > * Successful map reload without this > > > > path: > > > > * sync_map_state() will free it. > > > > @@ -1304,8 +1304,10 @@ out: > > > > return retval; > > > > > > > > fail: > > > > + condlog(0, "%s: error removing path. removing map %s", > > > > pp->dev, > > > > + mpp->alias); > > > > remove_map_and_stop_waiter(mpp, vecs); > > > > - return 1; > > > > + return 0; > > > > } > > > > > > > > static int > > > > -- > > dm-devel mailing list > > dm-devel@redhat.com > > https://listman.redhat.com/mailman/listinfo/dm-devel > > -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
On Wed, 2021-05-12 at 16:52 -0500, Benjamin Marzinski wrote: > On Wed, May 12, 2021 at 08:36:49PM +0000, Martin Wilck wrote: > > On Wed, 2021-05-12 at 14:53 -0500, Benjamin Marzinski wrote: > > > On Wed, May 12, 2021 at 11:38:08AM +0000, Martin Wilck wrote: > > > > On Tue, 2021-05-11 at 18:22 -0500, Benjamin Marzinski wrote: > > > So AFAICS, the only way for a path not to get removed is if you > > > succeed > > > with wait_for_udev or !need_do_map, or if you fail in domap. > > > > Agreed. Let's fix these comments. > > Yep. > > > > Since wait_for_udev can happen in more situations, > > > it's a lot harder to say what the right answer is. For > > > cli_add_path > > > and > > > uev_add_path, it seems like we want to know if the path was > > > really > > > removed. So returning failure there makes sense. For > > > cli_del_path > > > and > > > uev_remove_path, it seems like we want to avoid spurious error > > > messages > > > when everything went alright and we're just waiting to update the > > > map. > > > So returning success makes sense there. > > > > > > Perhaps the answer is to return symbolic values, to describe what > > > actually happened, rather than success or failure. > > > > This is what I meant. I didn't express myself clearly enough; I > > just > > thought that 0 doesn't have to mean "success". > > > > Sure. I'll add symbolic returns. > > > > > I think the callers just need to know if the path is still > > referenced > > somewhere. Acting appropriately is then up to the caller. You just > > proved that my cases a) and b) are actually equivalent, which is > > nice. > > Perhaps we need to introduce another return code indicating that > > the > > entire map had been removed (e.g. failure in setup_multipath()). > > The more important return to me seems to be an indication of whether > the > remove has been delayed. To make sure that we talk about the same thing: when you say "the remove has been delayed", you mean the case where we just set INIT_REMOVED, without actually deleting the path from pathvec etc., right? This is what I meant with "path is still referenced somewhere" in my previous post. Ack, this is of course the most important thing for the callers to know. > For uev_remove_path(), you don't want to > return failure just because the remove has been delayed. Otherwise > there > will be spurious error messages in the logs. With the introduction of INIT_REMOVED, I think we could do away with these error messages altogether. uev_remove_path() could actually be a void function. We *know* that at least INIT_REMOVED will be set, which means that that path will be treated by multipathd as if it didn't exist. The error message you're talking about would be the highly unhelpful "uevent trigger error" message - we might was well just ditch that message. We print much more meaningful messages in ev_remove_path(). > cli_del_path is a little > trickier. My biggest question with that is whether it would mess > with > people's scripts to add a reply message saying what happened. It > seems > like it should only fail if domap failed. But it would be nice to > tell > the user that the remove has been delayed, or that the map couldn't > be > reloaded and was removed as well. Same argument here. As far as multipathd is concerned, that path will be gone. We print "fail" if the domap() call failed, and we should continue to do so. We could add documentation saying that this means a "deferred removal". > > > > > However, this goes beyond the purpose of your patch. *If* we > > > > remove > > > > the > > > > map, returning 0 is correct for either a) or b). > > > > > > > > P.S. 2: I wonder if the logic in uev_update_path() is correct. > > > > Rather > > > > than calling uev_add_path() after rescan_path() directly, I > > > > think > > > > we > > > > should rather wait for another uevent (and possibly trigger > > > > another > > > > "add" event, I don't think "rescan" automatically generates > > > > one). > > > > > > > > > > Yep. You're correct. I'll fix that. > > Actually, I take it back. The code seems to work o.k. as is. The > uev_update_path() code checks if get_uid() now returns a different > value, instead of using get_vpd_sgio() like the recheck_wwid code > does. > This means that the uid_attribute must have already gotten updated > when > rescan_path() is called. So my real question is "is there any real > benefit to calling rescan_path() at all here". This code seemed to be > working correctly before we added it, except in the case where > uid_attribute wasn't getting updated (which recheck_wwid now will > hopefully catch). My point was that calling uev_add_path() right after rescan_path() is wrong, and I still think so - *if* we rescan, we shouldn't look at udev properties before we can be reasonably sure that the rescan has completed and has been processed by udev. I agree that calling rescan_path() in this code path is probably not helpful. Let's remove it. > If there is a benefit, then we have to be careful to only call it > once. > Otherwise, we could get stuck in an endless loop where we trigger an > add > uevent, which in turn triggers another add uevent, and so on. I don't see that risk, because uev_update_path() is only called for "change" uevents, not "add". Regards, Martin > > -Ben > > > > -Ben > > > > > > > > > > > > --- > > > > > multipathd/main.c | 6 ++++-- > > > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/multipathd/main.c b/multipathd/main.c > > > > > index 6090434c..4bdf14bd 100644 > > > > > --- a/multipathd/main.c > > > > > +++ b/multipathd/main.c > > > > > @@ -1284,7 +1284,7 @@ ev_remove_path (struct path *pp, struct > > > > > vectors * > > > > > vecs, int need_do_map) > > > > > > > > > > strlcpy(devt, pp->dev_t, > > > > > sizeof(devt)); > > > > > if (setup_multipath(vecs, mpp)) > > > > > - return 1; > > > > > + return 0; > > > > > /* > > > > > * Successful map reload without this > > > > > path: > > > > > * sync_map_state() will free it. > > > > > @@ -1304,8 +1304,10 @@ out: > > > > > return retval; > > > > > > > > > > fail: > > > > > + condlog(0, "%s: error removing path. removing map > > > > > %s", > > > > > pp->dev, > > > > > + mpp->alias); > > > > > remove_map_and_stop_waiter(mpp, vecs); > > > > > - return 1; > > > > > + return 0; > > > > > } > > > > > > > > > > static int > > > > > > -- > > > dm-devel mailing list > > > dm-devel@redhat.com > > > https://listman.redhat.com/mailman/listinfo/dm-devel > > > > -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel
diff --git a/multipathd/main.c b/multipathd/main.c index 6090434c..4bdf14bd 100644 --- a/multipathd/main.c +++ b/multipathd/main.c @@ -1284,7 +1284,7 @@ ev_remove_path (struct path *pp, struct vectors * vecs, int need_do_map) strlcpy(devt, pp->dev_t, sizeof(devt)); if (setup_multipath(vecs, mpp)) - return 1; + return 0; /* * Successful map reload without this path: * sync_map_state() will free it. @@ -1304,8 +1304,10 @@ out: return retval; fail: + condlog(0, "%s: error removing path. removing map %s", pp->dev, + mpp->alias); remove_map_and_stop_waiter(mpp, vecs); - return 1; + return 0; } static int
When ev_remove_path() returns success, callers assume that the path (and possibly the map) has been removed. When ev_remove_path() returns failure, callers assume that the path has not been removed. However, the path could be removed on both success or failure. This could cause callers to dereference the path after it was removed. Change ev_remove_path() to return success whenever the path is removed, even if the map was removed due to a failure when trying to reload it. Found by coverity. Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com> --- multipathd/main.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)