From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6694BC0044D for ; Mon, 16 Mar 2020 09:16:43 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EB4AF20674 for ; Mon, 16 Mar 2020 09:16:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB4AF20674 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5CA206B0003; Mon, 16 Mar 2020 05:16:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 57B5A6B0005; Mon, 16 Mar 2020 05:16:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 490226B0007; Mon, 16 Mar 2020 05:16:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0127.hostedemail.com [216.40.44.127]) by kanga.kvack.org (Postfix) with ESMTP id 326216B0003 for ; Mon, 16 Mar 2020 05:16:42 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id EA441180AD802 for ; Mon, 16 Mar 2020 09:16:41 +0000 (UTC) X-FDA: 76600670202.06.ghost04_1d550a6091d1c X-HE-Tag: ghost04_1d550a6091d1c X-Filterd-Recvd-Size: 8911 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Mon, 16 Mar 2020 09:16:41 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id DA0D6AC69; Mon, 16 Mar 2020 09:16:36 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 83CDC1E10DA; Mon, 16 Mar 2020 10:16:33 +0100 (CET) Date: Mon, 16 Mar 2020 10:16:33 +0100 From: Jan Kara To: Matthew Wilcox Cc: Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH 1/8] xarray: Fix premature termination of xas_for_each_marked() Message-ID: <20200316091633.GA12783@quack2.suse.cz> References: <20200204142514.15826-1-jack@suse.cz> <20200204142514.15826-2-jack@suse.cz> <20200312214548.GL22433@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200312214548.GL22433@bombadil.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) 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 12-03-20 14:45:48, Matthew Wilcox wrote: > Hi Jan, > > I fixed this in a different way ... also, I added a test to the test-suite > so this shouldn't regress. Thanks for writing the commit message ;-) > > From 7e934cf5ace1dceeb804f7493fa28bb697ed3c52 Mon Sep 17 00:00:00 2001 > From: "Matthew Wilcox (Oracle)" > Date: Thu, 12 Mar 2020 17:29:11 -0400 > Subject: [PATCH] xarray: Fix early termination of xas_for_each_marked > > xas_for_each_marked() is using entry == NULL as a termination condition > of the iteration. When xas_for_each_marked() is used protected only by > RCU, this can however race with xas_store(xas, NULL) in the following > way: > > TASK1 TASK2 > page_cache_delete() find_get_pages_range_tag() > xas_for_each_marked() > xas_find_marked() > off = xas_find_chunk() > > xas_store(&xas, NULL) > xas_init_marks(&xas); > ... > rcu_assign_pointer(*slot, NULL); > entry = xa_entry(off); > > And thus xas_for_each_marked() terminates prematurely possibly leading > to missed entries in the iteration (translating to missing writeback of > some pages or a similar problem). > > If we find a NULL entry that has been marked, skip it (unless we're trying > to allocate an entry). > > Reported-by: Jan Kara > CC: stable@vger.kernel.org > Fixes: ef8e5717db01 ("page cache: Convert delete_batch to XArray") > Signed-off-by: Matthew Wilcox (Oracle) The patch looks good to me. Thanks for looking into this. You can add: Reviewed-by: Jan Kara Honza > --- > include/linux/xarray.h | 6 +- > lib/xarray.c | 2 + > tools/testing/radix-tree/Makefile | 4 +- > tools/testing/radix-tree/iteration_check_2.c | 87 ++++++++++++++++++++ > tools/testing/radix-tree/main.c | 1 + > tools/testing/radix-tree/test.h | 1 + > 6 files changed, 98 insertions(+), 3 deletions(-) > create mode 100644 tools/testing/radix-tree/iteration_check_2.c > > diff --git a/include/linux/xarray.h b/include/linux/xarray.h > index a491653d8882..14c893433139 100644 > --- a/include/linux/xarray.h > +++ b/include/linux/xarray.h > @@ -1648,6 +1648,7 @@ static inline void *xas_next_marked(struct xa_state *xas, unsigned long max, > xa_mark_t mark) > { > struct xa_node *node = xas->xa_node; > + void *entry; > unsigned int offset; > > if (unlikely(xas_not_node(node) || node->shift)) > @@ -1659,7 +1660,10 @@ static inline void *xas_next_marked(struct xa_state *xas, unsigned long max, > return NULL; > if (offset == XA_CHUNK_SIZE) > return xas_find_marked(xas, max, mark); > - return xa_entry(xas->xa, node, offset); > + entry = xa_entry(xas->xa, node, offset); > + if (!entry) > + return xas_find_marked(xas, max, mark); > + return entry; > } > > /* > diff --git a/lib/xarray.c b/lib/xarray.c > index f448bcd263ac..e9e641d3c0c3 100644 > --- a/lib/xarray.c > +++ b/lib/xarray.c > @@ -1208,6 +1208,8 @@ void *xas_find_marked(struct xa_state *xas, unsigned long max, xa_mark_t mark) > } > > entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset); > + if (!entry && !(xa_track_free(xas->xa) && mark == XA_FREE_MARK)) > + continue; > if (!xa_is_node(entry)) > return entry; > xas->xa_node = xa_to_node(entry); > diff --git a/tools/testing/radix-tree/Makefile b/tools/testing/radix-tree/Makefile > index 397d6b612502..aa6abfe0749c 100644 > --- a/tools/testing/radix-tree/Makefile > +++ b/tools/testing/radix-tree/Makefile > @@ -7,8 +7,8 @@ LDLIBS+= -lpthread -lurcu > TARGETS = main idr-test multiorder xarray > CORE_OFILES := xarray.o radix-tree.o idr.o linux.o test.o find_bit.o bitmap.o > OFILES = main.o $(CORE_OFILES) regression1.o regression2.o regression3.o \ > - regression4.o \ > - tag_check.o multiorder.o idr-test.o iteration_check.o benchmark.o > + regression4.o tag_check.o multiorder.o idr-test.o iteration_check.o \ > + iteration_check_2.o benchmark.o > > ifndef SHIFT > SHIFT=3 > diff --git a/tools/testing/radix-tree/iteration_check_2.c b/tools/testing/radix-tree/iteration_check_2.c > new file mode 100644 > index 000000000000..aac5c50a3674 > --- /dev/null > +++ b/tools/testing/radix-tree/iteration_check_2.c > @@ -0,0 +1,87 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +/* > + * iteration_check_2.c: Check that deleting a tagged entry doesn't cause > + * an RCU walker to finish early. > + * Copyright (c) 2020 Oracle > + * Author: Matthew Wilcox > + */ > +#include > +#include "test.h" > + > +static volatile bool test_complete; > + > +static void *iterator(void *arg) > +{ > + XA_STATE(xas, arg, 0); > + void *entry; > + > + rcu_register_thread(); > + > + while (!test_complete) { > + xas_set(&xas, 0); > + rcu_read_lock(); > + xas_for_each_marked(&xas, entry, ULONG_MAX, XA_MARK_0) > + ; > + rcu_read_unlock(); > + assert(xas.xa_index >= 100); > + } > + > + rcu_unregister_thread(); > + return NULL; > +} > + > +static void *throbber(void *arg) > +{ > + struct xarray *xa = arg; > + > + rcu_register_thread(); > + > + while (!test_complete) { > + int i; > + > + for (i = 0; i < 100; i++) { > + xa_store(xa, i, xa_mk_value(i), GFP_KERNEL); > + xa_set_mark(xa, i, XA_MARK_0); > + } > + for (i = 0; i < 100; i++) > + xa_erase(xa, i); > + } > + > + rcu_unregister_thread(); > + return NULL; > +} > + > +void iteration_test2(unsigned test_duration) > +{ > + pthread_t threads[2]; > + DEFINE_XARRAY(array); > + int i; > + > + printv(1, "Running iteration test 2 for %d seconds\n", test_duration); > + > + test_complete = false; > + > + xa_store(&array, 100, xa_mk_value(100), GFP_KERNEL); > + xa_set_mark(&array, 100, XA_MARK_0); > + > + if (pthread_create(&threads[0], NULL, iterator, &array)) { > + perror("create iterator thread"); > + exit(1); > + } > + if (pthread_create(&threads[1], NULL, throbber, &array)) { > + perror("create throbber thread"); > + exit(1); > + } > + > + sleep(test_duration); > + test_complete = true; > + > + for (i = 0; i < 2; i++) { > + if (pthread_join(threads[i], NULL)) { > + perror("pthread_join"); > + exit(1); > + } > + } > + > + xa_destroy(&array); > +} > diff --git a/tools/testing/radix-tree/main.c b/tools/testing/radix-tree/main.c > index 7a22d6e3732e..f2cbc8e5b97c 100644 > --- a/tools/testing/radix-tree/main.c > +++ b/tools/testing/radix-tree/main.c > @@ -311,6 +311,7 @@ int main(int argc, char **argv) > regression4_test(); > iteration_test(0, 10 + 90 * long_run); > iteration_test(7, 10 + 90 * long_run); > + iteration_test2(10 + 90 * long_run); > single_thread_tests(long_run); > > /* Free any remaining preallocated nodes */ > diff --git a/tools/testing/radix-tree/test.h b/tools/testing/radix-tree/test.h > index 1ee4b2c0ad10..34dab4d18744 100644 > --- a/tools/testing/radix-tree/test.h > +++ b/tools/testing/radix-tree/test.h > @@ -34,6 +34,7 @@ void xarray_tests(void); > void tag_check(void); > void multiorder_checks(void); > void iteration_test(unsigned order, unsigned duration); > +void iteration_test2(unsigned duration); > void benchmark(void); > void idr_checks(void); > void ida_tests(void); > -- > 2.25.1 > -- Jan Kara SUSE Labs, CR