Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > On Tue, Dec 07, 2021 at 11:19:35AM +0000, David Howells wrote: > > Taking sb_writers whilst holding mmap_lock isn't allowed and will result in > > a lockdep warning like that below. The problem comes from cachefiles > > needing to take the sb_writers lock in order to do a write to the cache, > > but being asked to do this by netfslib called from readpage, readahead or > > write_begin[1]. > > Isn't it taking sb_writers _on a different filesystem_? So there's not > a real deadlock here, just a need to tell lockdep that this is a > different subclass of lock? Jann thinks it can be turned into a real deadlock. See the link I put in the patch description: > > Link: https://lore.kernel.org/r/20210922110420.GA21576@xxxxxxxxxxxxxx/ [1] David
