On Thu, Jan 10, 2019 at 11:48 AM Kirill Tkhai <[email protected]> wrote: > > Hi, Miklos, > > any comments about this?
Is there a reproducer? ISTR that fsx-linux with mmaps enabled was good for stressing the writeback_cache code. Thanks, Miklos > > On 26.11.2018 12:46, Kirill Tkhai wrote: > > Checking for FR_PENDING in fuse_writepage_in_flight() is racy. > > It does not guarantee the first request in misc.write.next list > > is not in userspace, since there we take fc->lock, while > > fuse_dev_do_read() takes fiq->waitq.lock: > > > > fuse_dev_read() fuse_writepage_in_flight() > > test_bit(FR_PENDING) > > clear_bit(FR_PENDING) > > handle old_req->pages[0] in userspace > > > > copy_highpage(old_req->pages[0], page) > > ^^^^^ > > userspace never sees this pages > > > > The only reliable way to determ, whether we are able to replace > > old_req's page, is to completely skip the first request in the list. > > This patch makes the function to do that. > > > > Signed-off-by: Kirill Tkhai <[email protected]> > > --- > > fs/fuse/file.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > > index b52f9baaa3e7..c6650c68b31a 100644 > > --- a/fs/fuse/file.c > > +++ b/fs/fuse/file.c > > @@ -1740,6 +1740,7 @@ static bool fuse_writepage_in_flight(struct fuse_req > > *new_req, > > { > > struct fuse_conn *fc = get_fuse_conn(new_req->inode); > > struct fuse_inode *fi = get_fuse_inode(new_req->inode); > > + struct fuse_req *first_req; > > struct fuse_req *tmp; > > struct fuse_req *old_req; > > bool found = false; > > @@ -1764,6 +1765,7 @@ static bool fuse_writepage_in_flight(struct fuse_req > > *new_req, > > } > > > > new_req->num_pages = 1; > > + first_req = old_req; > > for (tmp = old_req; tmp != NULL; tmp = tmp->misc.write.next) { > > BUG_ON(tmp->inode != new_req->inode); > > curr_index = tmp->misc.write.in.offset >> PAGE_SHIFT; > > @@ -1773,7 +1775,7 @@ static bool fuse_writepage_in_flight(struct fuse_req > > *new_req, > > } > > } > > > > - if (old_req->num_pages == 1 && test_bit(FR_PENDING, &old_req->flags)) > > { > > + if (old_req->num_pages == 1 && old_req != first_req) { > > struct backing_dev_info *bdi = > > inode_to_bdi(page->mapping->host); > > > > copy_highpage(old_req->pages[0], page); > >
