On Fri, Sep 9, 2016 at 9:42 PM, Johannes Weiner <han...@cmpxchg.org> wrote: > Hi Miklos, > > On Fri, Sep 09, 2016 at 04:32:49PM +0200, Miklos Szeredi wrote: >> On Fri, Sep 9, 2016 at 3:34 PM, Antonio SJ Musumeci <trape...@spawn.link> >> wrote: >> > https://gist.github.com/bauruine/3bc00075c4d0b5b3353071d208ded30f >> > https://github.com/trapexit/mergerfs/issues/295 >> > >> > I've some users which are having issues with my filesystem where the >> > system's load increases and then the kernel panics. >> > >> > Has anyone seen this before? >> >> Quite possibly this is caused by fuse, but the BUG is deep in mm >> territory and I have zero clue about what it means. >> >> Hannes, can you please look a the above crash in mm/workingset.c? > > The MM maintains a reclaimable list of page cache tree nodes that have > gone empty (all pages evicted) except for the shadow entries reclaimed > pages leave behind. When faulting a regular page back into such a node > the code in page_cache_tree_insert() removes it from the list again: > > workingset_node_pages_inc(node); > /* > * Don't track node that contains actual pages. > * > * Avoid acquiring the list_lru lock if already > * untracked. The list_empty() test is safe as > * node->private_list is protected by > * mapping->tree_lock. > */ > if (!list_empty(&node->private_list)) > list_lru_del(&workingset_shadow_nodes, > &node->private_list); > > The BUG_ON() triggers when we later walk the reclaimable list and find > a radix tree node that has actual pages in it. This could happen when > pages are inserted into a mapping without using add_to_page_cache and > related functions. Does that maybe ring a bell?
Fuse allows pages to be spliced into the page cache when reading the file. It does this with replace_page_cache_page(), which is an atomic version of delete_from_page_cache()+add_to_page_cache(). Fuse is the only user of replace_page_cache_page(), so I imagine bugs can more easily escape notice than the more commonly used variants. Could you please take a look at this function. "git blame" shows that it's older than the add/remove variants, but I haven't gone into the details. Thanks, Miklos
