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[141.146.126.79]) by mx.google.com with ESMTPS id g12si374119ita.133.2019.02.04.10.25.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 04 Feb 2019 10:25:45 -0800 (PST) Received-SPF: pass (google.com: domain of dan.carpenter@oracle.com designates 141.146.126.79 as permitted sender) client-ip=141.146.126.79; Authentication-Results: mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2018-07-02 header.b=bvLVw1b4; spf=pass (google.com: domain of dan.carpenter@oracle.com designates 141.146.126.79 as permitted sender) smtp.mailfrom=dan.carpenter@oracle.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: from pps.filterd (aserp2130.oracle.com [127.0.0.1]) by aserp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x14INmG5068339; Mon, 4 Feb 2019 18:25:39 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : mime-version : content-type : in-reply-to; s=corp-2018-07-02; bh=guEa4pAdTVI2vasSBUcrIKQQiPIM0OIavHgpDPBgRjM=; b=bvLVw1b4DoAfTWs1UqbNPyuxP4NgDc8/4239FJmOvU1SWVtC9/5b6rsNnTeiR8Jn6Y5q r8FgSzlZwPsTBLrxc/4No03OnX2o+wPAFwX/AC29GMt7z/epS4VF+3ymANI8NSS6LgpV qZPE7/lclzXOZRkfH/O0IRqs82VPpPgJcJ4z9ts7NQRoyB5Knva0FEqDpjPE4Sjy+5K9 yWY5IH/iNTUEmUcjfnd8rXWyhjjY89HKcLEw40li8Y21vRBjGc1oyzQaUV0DrrD/x0kM 5cSSEFxzWRxKZIyactgXWpGt6PQ70oxNKhp/A2JWvjZvx9TGi/FcZ6FYJgvfqLcZi8nq nQ== Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234]) by aserp2130.oracle.com with ESMTP id 2qd97eptn8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 04 Feb 2019 18:25:39 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id x14IPcxX020616 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 4 Feb 2019 18:25:38 GMT Received: from abhmp0012.oracle.com (abhmp0012.oracle.com [141.146.116.18]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x14IPcfX013011; Mon, 4 Feb 2019 18:25:38 GMT Received: from kadam (/197.157.0.20) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 04 Feb 2019 18:25:32 +0000 Date: Mon, 4 Feb 2019 21:24:21 +0300 From: Dan Carpenter To: =?iso-8859-1?B?Suly9G1l?= Glisse Cc: linux-mm@kvack.org, kernel-janitors@vger.kernel.org, Andrew Morton , Stephen Rothwell Subject: [PATCH v2] mm/hmm: potential deadlock in nonblocking code Message-ID: <20190204182304.GA8756@kadam> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190204132043.GA16485@kadam> X-Mailer: git-send-email haha only kidding User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9157 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1902040141 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: There is a deadlock bug when these functions are used in nonblocking mode. The else side of the if/else statement is only meant to be taken in when the code is used in blocking mode. But, unfortunately, the way the code is now, if we're in non-blocking mode and we succeed in taking the lock then we do the else statement. The else side tries to take lock a second time which results in a deadlock. Fixes: a3402cb621c1 ("mm/hmm: improve driver API to work and wait over a range") Signed-off-by: Dan Carpenter --- V2: improve the style and tweak the commit description hmm.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/mm/hmm.c b/mm/hmm.c index e14e0aa4d2cb..3c9781037918 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -207,11 +207,12 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn, update.event = HMM_UPDATE_INVALIDATE; update.blockable = nrange->blockable; - if (!nrange->blockable && !mutex_trylock(&hmm->lock)) { + if (nrange->blockable) + mutex_lock(&hmm->lock); + else if (!mutex_trylock(&hmm->lock)) { ret = -EAGAIN; goto out; - } else - mutex_lock(&hmm->lock); + } hmm->notifiers++; list_for_each_entry(range, &hmm->ranges, list) { if (update.end < range->start || update.start >= range->end) @@ -221,12 +222,12 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn, } mutex_unlock(&hmm->lock); - - if (!nrange->blockable && !down_read_trylock(&hmm->mirrors_sem)) { + if (nrange->blockable) + down_read(&hmm->mirrors_sem); + else if (!down_read_trylock(&hmm->mirrors_sem)) { ret = -EAGAIN; goto out; - } else - down_read(&hmm->mirrors_sem); + } list_for_each_entry(mirror, &hmm->mirrors, list) { int ret;