AZL-80726

In the Linux kernel, the following vulnerability has been resolved:

drbd: fix "LOGIC BUG" in drbdalbeginiononblock()

Even though we check that we "should" be able to do lcgetcumulative() while holding the device->allock spinlock, it may still fail, if some other code path decided to do lctry_lock() with bad timing.

If that happened, we logged "LOGIC BUG for enr=...", but still did not return an error.

The rest of the code now assumed that this request has references for the relevant activity log extents.

The implcations are that during an active resync, mutual exclusivity of resync versus application IO is not guaranteed. And a potential crash at this point may not realizs that these extents could have been target of in-flight IO and would need to be resynced just in case.

Also, once the request completes, it will give up activity log references it does not even hold, which will trigger a BUGON(refcnt == 0) in lcput().

Fix:

Do not crash the kernel for a condition that is harmless during normal operation: also catch "e->refcnt == 0", not only "e == NULL" when being noisy about "alcompleteio() called on inactive extent %u\n".

And do not try to be smart and "guess" whether something will work, then be surprised when it does not. Deal with the fact that it may or may not work. If it does not, remember a possible "partially in activity log" state (only possible for requests that cross extent boundaries), and return an error code from drbdalbeginiononblock().

A latter call for the same request will then resume from where we left off.