On Thu, Apr 03, 2025 at 08:06:53PM +1030, Qu Wenruo wrote: > Recently I hit a bug when developing the large folios support for btrfs. > > That we call filemap_get_folios_contig(), then lock each returned folio. > (We also have a case where we unlock each returned folio) > > However since a large folio can be returned several times in the batch, > this obviously makes a deadlock, as btrfs is trying to lock the same > folio more than once. Sorry, what? A large folio should only be returned once. xas_next() moves to the next folio. How is it possible that filemap_get_folios_contig() returns the same folio more than once? > Then I looked into the caller of filemap_get_folios_contig() inside > mm/gup, and it indeed does the correct skip. ... that code looks wrong to me.
