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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id g5si5180681pfi.60.2019.03.11.08.09.48 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 11 Mar 2019 08:09:48 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=Bd7ZvUX2; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=WBXiJsth6ZRy4NnXvBEm40XbIfkraeDBimeU3qelFzU=; b=Bd7ZvUX2y4PxO1EIn4KySo+3Q eteJtV//cZGYPMH5OL5vGuOHVk9+SgU3zPSwU8836Bm/mfFWELjsiXId8ieTyy8jekyQHhdHCXuWe T1fHnDzr+SPYy6FKgsl6iOHGPcqIzi3M15vR+pXmHKq1wrd5zauFP2NPlDHWh/aHXG76TSECdxVmN 30Z8Q8fRb+EY74Ol1rHXThvErA62J1HtwmWP416mwOl0ChWxJRi6UFB7k6sl2TVqPmijGljMRBhmR xRbcDeOZAXzRWzfGf+RHWt4CeLySYB4CAGMVJQZM21TWtDfg3CwcxtyG08bk7GRlNbY/WwLbwuZ0B BnwtoY5mA==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1h3MYl-0004UM-Ib; Mon, 11 Mar 2019 15:09:47 +0000 Date: Mon, 11 Mar 2019 08:09:47 -0700 From: Matthew Wilcox To: Dan Williams Cc: Linux MM , linux-nvdimm , linux-fsdevel , "Barror, Robert" Subject: Re: Hang / zombie process from Xarray page-fault conversion (bisected) Message-ID: <20190311150947.GD19508@bombadil.infradead.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 07, 2019 at 10:16:17PM -0800, Dan Williams wrote: > Hi Willy, > > We're seeing a case where RocksDB hangs and becomes defunct when > trying to kill the process. v4.19 succeeds and v4.20 fails. Robert was > able to bisect this to commit b15cd800682f "dax: Convert page fault > handlers to XArray". > > I see some direct usage of xa_index and wonder if there are some more > pmd fixups to do? > > Other thoughts? I don't see why killing a process would have much to do with PMD misalignment. The symptoms (hanging on a signal) smell much more like leaving a locked entry in the tree. Is this easy to reproduce? Can you get /proc/$pid/stack for a hung task?