From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 27 Sep 2018 13:13:54 +0200 From: Jan Kara To: Barret Rhoden Cc: Dan Williams , linux-nvdimm@lists.01.org, hch@lst.de, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jack@suse.cz, ross.zwisler@linux.intel.com Subject: Re: [PATCH v5 07/11] filesystem-dax: Introduce dax_lock_mapping_entry() Message-ID: <20180927111354.GA16469@quack2.suse.cz> References: <153074042316.27838.17319837331947007626.stgit@dwillia2-desk3.amr.corp.intel.com> <153074046078.27838.5465590228767136915.stgit@dwillia2-desk3.amr.corp.intel.com> <20180924115721.75893931@gnomeregan.cam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180924115721.75893931@gnomeregan.cam.corp.google.com> Sender: owner-linux-mm@kvack.org List-ID: On Mon 24-09-18 11:57:21, Barret Rhoden wrote: > Hi Dan - > > On 2018-07-04 at 14:41 Dan Williams wrote: > [snip] > > diff --git a/fs/dax.c b/fs/dax.c > > index 4de11ed463ce..57ec272038da 100644 > > --- a/fs/dax.c > > +++ b/fs/dax.c > [snip] > > +bool dax_lock_mapping_entry(struct page *page) > > +{ > > + pgoff_t index; > > + struct inode *inode; > > + bool did_lock = false; > > + void *entry = NULL, **slot; > > + struct address_space *mapping; > > + > > + rcu_read_lock(); > > + for (;;) { > > + mapping = READ_ONCE(page->mapping); > > + > > + if (!dax_mapping(mapping)) > > + break; > > + > > + /* > > + * In the device-dax case there's no need to lock, a > > + * struct dev_pagemap pin is sufficient to keep the > > + * inode alive, and we assume we have dev_pagemap pin > > + * otherwise we would not have a valid pfn_to_page() > > + * translation. > > + */ > > + inode = mapping->host; > > + if (S_ISCHR(inode->i_mode)) { > > + did_lock = true; > > + break; > > + } > > + > > + xa_lock_irq(&mapping->i_pages); > > + if (mapping != page->mapping) { > > + xa_unlock_irq(&mapping->i_pages); > > + continue; > > + } > > + index = page->index; > > + > > + entry = __get_unlocked_mapping_entry(mapping, index, &slot, > > + entry_wait_revalidate); > > + if (!entry) { > > + xa_unlock_irq(&mapping->i_pages); > > + break; > > + } else if (IS_ERR(entry)) { > > + WARN_ON_ONCE(PTR_ERR(entry) != -EAGAIN); > > + continue; > > In the IS_ERR case, do you need to xa_unlock the mapping? It looks > like you'll deadlock the next time around the loop. Yep, that looks certainly wrong. I'll send a fix. Honza -- Jan Kara SUSE Labs, CR