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Is it recoverable ? As described in the commit message above, the specific situation where this happens is when we try to pin memfd folios before they are faulted-in. Although, this is a valid thing to do, it is not the regular or the common use-case. Let me explain this further with the following scenarios: 1) hugetlbfs_file_mmap() memfd_alloc_folio() hugetlb_fault() 2) memfd_alloc_folio() hugetlbfs_file_mmap() hugetlb_fault() 3) hugetlbfs_file_mmap() hugetlb_fault() alloc_hugetlb_folio() 3) is the most common use-case where first a memfd is allocated followed by mmap(), user writes/updates and then the relevant folios are pinned (memfd_pin_folios()). The BUG this patch is fixing occurs in 2) because we try to pin the folios before hugetlbfs_file_mmap() is called. So, in this situation we try to allocate the folios before pinning them but since we di= d not make any reservations, resv_huge_pages would be 0, leading to this issu= e. >=20 > I'm suspecting we don't know. >=20 > > > > > > Fixes: 26a8ea80929c ("mm/hugetlb: fix memfd_pin_folios > resv_huge_pages leak") >=20 > How was this arrived at? This is merely the patch which added the assert= ion. Right, 26a8ea80929c is indeed the commit that introduced code that led to t= his BUG/crash. Would this not qualify for Fixes? >=20 > > > Reported-by: syzbot+a504cb5bae4fe117ba94@syzkaller.appspotmail.com > > > Closes: https://syzkaller.appspot.com/bug?extid=3Da504cb5bae4fe117ba9= 4 >=20 > I can't find any mailing report/discussion of this. The Closes: takes > us to the syskaller report which is a bit of a dead end. My understanding is that the Closes tag can be associated with a URL for a public bugtracker like Syzkaller. Would the following be a better Closes = link: https://lore.kernel.org/all/677928b5.050a0220.3b53b0.004d.GAE@google.com/T/ >=20 > I agree with the patch - converting a BUG into a WARN+recover is a good > thing but as far as I can tell, we don't know what's causing this > situation. >=20 > syskaller has a C reproducer, if anyone is feeling brave. The udmabuf selftest added in patch #3 of the other series can also reprodu= ce=20 this issue and is a lot simpler. Thanks, Vivek