From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 19 Jun 2018 10:16:38 -0700 From: Matthew Wilcox To: Ross Zwisler , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jan Kara , Jeff Layton , Lukas Czerner , Christoph Hellwig , Goldwyn Rodrigues , Nicholas Piggin , Ryusuke Konishi , linux-nilfs@vger.kernel.org, Jaegeuk Kim , Chao Yu , linux-f2fs-devel@lists.sourceforge.net Subject: Re: [PATCH v14 00/74] Convert page cache to XArray Message-ID: <20180619171638.GE1438@bombadil.infradead.org> References: <20180617020052.4759-1-willy@infradead.org> <20180619031257.GA12527@linux.intel.com> <20180619092230.GA1438@bombadil.infradead.org> <20180619164037.GA6679@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180619164037.GA6679@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: On Tue, Jun 19, 2018 at 10:40:37AM -0600, Ross Zwisler wrote: > On Tue, Jun 19, 2018 at 02:22:30AM -0700, Matthew Wilcox wrote: > > On Mon, Jun 18, 2018 at 09:12:57PM -0600, Ross Zwisler wrote: > > > Hit another deadlock. This one reproduces 100% of the time in my setup with > > > XFS + DAX + generic/340. It doesn't reproduce for me at all with > > > next-20180615. Here's the output from "echo w > /proc/sysrq-trigger": > > > > *sigh*. I wonder what the differences are between our setups ... > > > > > [ 92.849119] sysrq: SysRq : Show Blocked State > > > [ 92.850506] task PC stack pid father > > > [ 92.852299] holetest D 0 1651 1466 0x00000000 > > > [ 92.853912] Call Trace: > > > [ 92.854610] __schedule+0x2c5/0xad0 > > > [ 92.855612] schedule+0x36/0x90 > > > [ 92.856602] get_unlocked_entry+0xce/0x120 > > > [ 92.857756] ? dax_insert_entry+0x2b0/0x2b0 > > > [ 92.858931] grab_mapping_entry+0x19e/0x250 > > > [ 92.860119] dax_iomap_pte_fault+0x115/0x1140 > > > [ 92.860836] dax_iomap_fault+0x37/0x40 > > ... > > > This looks very similar to the one I reported last week with generic/269. > > > > Yeah, another missing wakeup, no doubt. Can you bisect this? That was > > how I found the last one; bisected it to a single patch and stared very > > hard at the patch until I saw it. I'm not going to be in a position to > > tinker with my DAX setup until the first week of July. > > It bisected to this commit: > > b4b4daa7e8fb0ad0fee35d3e28d00e97c849a6cb is the first bad commit > commit b4b4daa7e8fb0ad0fee35d3e28d00e97c849a6cb > Author: Matthew Wilcox > Date: Thu Mar 29 22:58:27 2018 -0400 > > dax: Convert page fault handlers to XArray > > This is the last part of DAX to be converted to the XArray so > remove all the old helper functions. > > Signed-off-by: Matthew Wilcox I think I see a bug. No idea if it's the one you're hitting ;-) I had been intending to not use the 'entry' to decide whether we were waiting on a 2MB or 4kB page, but rather the xas. I shelved that idea, but not before dropping the DAX_PMD flag being passed from the PMD pagefault caller. So if I put that back ... diff --git a/fs/dax.c b/fs/dax.c index 9919b6b545fb..75cc160d2f0b 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -367,13 +367,13 @@ static struct page *dax_busy_page(void *entry) * a VM_FAULT code, encoded as an xarray internal entry. The ERR_PTR values * overlap with xarray value entries. */ -static -void *grab_mapping_entry(struct xa_state *xas, struct address_space *mapping) +static void *grab_mapping_entry(struct xa_state *xas, + struct address_space *mapping, unsigned long size) { bool pmd_downgrade = false; /* splitting 2MiB entry into 4k entries? */ void *locked = dax_make_entry(pfn_to_pfn_t(0), - DAX_EMPTY | DAX_LOCKED); - void *unlocked = dax_make_entry(pfn_to_pfn_t(0), DAX_EMPTY); + size | DAX_EMPTY | DAX_LOCKED); + void *unlocked = dax_make_entry(pfn_to_pfn_t(0), size | DAX_EMPTY); void *entry; retry: @@ -1163,7 +1163,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp, if (write && !vmf->cow_page) flags |= IOMAP_WRITE; - entry = grab_mapping_entry(&xas, mapping); + entry = grab_mapping_entry(&xas, mapping, 0); if (xa_is_internal(entry)) { ret = xa_to_internal(entry); goto out; @@ -1396,7 +1396,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp, * page is already in the tree, for instance), it will return * VM_FAULT_FALLBACK. */ - entry = grab_mapping_entry(&xas, mapping); + entry = grab_mapping_entry(&xas, mapping, DAX_PMD); if (xa_is_internal(entry)) { result = xa_to_internal(entry); goto fallback;