From patchwork Fri Dec 1 19:50:59 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. 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McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, "Paul E. McKenney" , Alexander Viro , Subject: [PATCH tip/core/rcu 04/21] fs/dcache: Use release-acquire for name/length update Date: Fri, 1 Dec 2017 11:50:59 -0800 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20171201195053.GA23494@linux.vnet.ibm.com> References: <20171201195053.GA23494@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17120119-0008-0000-0000-000002A93782 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008137; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000243; SDB=6.00953999; UDB=6.00482085; IPR=6.00734074; BA=6.00005726; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018295; XFM=3.00000015; UTC=2017-12-01 19:51:22 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17120119-0009-0000-0000-00003778CAD6 Message-Id: <1512157876-24665-4-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:, , definitions=2017-12-01_05:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1712010232 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The code in __d_alloc() carefully orders filling in the NUL character of the name (and the length, hash, and the name itself) with assigning of the name itself. However, prepend_name() does not order the accesses to the ->name and ->len fields, other than on TSO systems. This commit therefore replaces prepend_name()'s READ_ONCE() of ->name with an smp_load_acquire(), which orders against the subsequent READ_ONCE() of ->len. Because READ_ONCE() now incorporates smp_read_barrier_depends(), prepend_name()'s smp_read_barrier_depends() is removed. Finally, to save a line, the smp_wmb()/store pair in __d_alloc() is replaced by smp_store_release(). Signed-off-by: Paul E. McKenney Cc: Alexander Viro Cc: --- fs/dcache.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 5c7df1df81ff..379dce86f001 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1636,8 +1636,7 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name) dname[name->len] = 0; /* Make sure we always see the terminating NUL character */ - smp_wmb(); - dentry->d_name.name = dname; + smp_store_release(&dentry->d_name.name, dname); /* ^^^ */ dentry->d_lockref.count = 1; dentry->d_flags = 0; @@ -3047,17 +3046,14 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen) * retry it again when a d_move() does happen. So any garbage in the buffer * due to mismatched pointer and length will be discarded. * - * Data dependency barrier is needed to make sure that we see that terminating - * NUL. Alpha strikes again, film at 11... + * Load acquire is needed to make sure that we see that terminating NUL. */ static int prepend_name(char **buffer, int *buflen, const struct qstr *name) { - const char *dname = READ_ONCE(name->name); + const char *dname = smp_load_acquire(&name->name); /* ^^^ */ u32 dlen = READ_ONCE(name->len); char *p; - smp_read_barrier_depends(); - *buflen -= dlen + 1; if (*buflen < 0) return -ENAMETOOLONG;