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=-10.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,USER_AGENT_GIT 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 7FF3EC43441 for ; Thu, 29 Nov 2018 14:26:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3D6AE2146D for ; Thu, 29 Nov 2018 14:26:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="oT+vMXQ2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3D6AE2146D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387418AbeK3BcI (ORCPT ); Thu, 29 Nov 2018 20:32:08 -0500 Received: from mail.kernel.org ([198.145.29.99]:60022 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387394AbeK3BcH (ORCPT ); Thu, 29 Nov 2018 20:32:07 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B26042146D; Thu, 29 Nov 2018 14:26:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1543501594; bh=oE6m1lSkdrEXKP7sjUddJauIeYVCUFtNTeePIizf5Y0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oT+vMXQ2z9Bk/KFQhX5P5fZRq/3Cd00mn24IIea0/Unv1y/oo3xn9qvZ727Woh7Dm 7ZMettqvwp+TI9WWcl25Cn7uPj9YraVt2C+xzL5ziDnTcAEbV+XN6mCnMaEzKBNSHL v8AaT3FPIpA8EyROrJTnhCWBY7erg99lNhgbNsOw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vitaly Wool , Jongseok Kim , Snild Dolkow , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 4.14 062/100] z3fold: fix possible reclaim races Date: Thu, 29 Nov 2018 15:12:32 +0100 Message-Id: <20181129140104.378401940@linuxfoundation.org> X-Mailer: git-send-email 2.19.2 In-Reply-To: <20181129140058.768942700@linuxfoundation.org> References: <20181129140058.768942700@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit ca0246bb97c23da9d267c2107c07fb77e38205c9 ] Reclaim and free can race on an object which is basically fine but in order for reclaim to be able to map "freed" object we need to encode object length in the handle. handle_to_chunks() is then introduced to extract object length from a handle and use it during mapping. Moreover, to avoid racing on a z3fold "headless" page release, we should not try to free that page in z3fold_free() if the reclaim bit is set. Also, in the unlikely case of trying to reclaim a page being freed, we should not proceed with that page. While at it, fix the page accounting in reclaim function. This patch supersedes "[PATCH] z3fold: fix reclaim lock-ups". Link: http://lkml.kernel.org/r/20181105162225.74e8837d03583a9b707cf559@gmail.com Signed-off-by: Vitaly Wool Signed-off-by: Jongseok Kim Reported-by-by: Jongseok Kim Reviewed-by: Snild Dolkow Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/z3fold.c | 101 ++++++++++++++++++++++++++++++++-------------------- 1 file changed, 62 insertions(+), 39 deletions(-) diff --git a/mm/z3fold.c b/mm/z3fold.c index f33403d718ac..2813cdfa46b9 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -99,6 +99,7 @@ struct z3fold_header { #define NCHUNKS ((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT) #define BUDDY_MASK (0x3) +#define BUDDY_SHIFT 2 /** * struct z3fold_pool - stores metadata for each z3fold pool @@ -145,7 +146,7 @@ enum z3fold_page_flags { MIDDLE_CHUNK_MAPPED, NEEDS_COMPACTING, PAGE_STALE, - UNDER_RECLAIM + PAGE_CLAIMED, /* by either reclaim or free */ }; /***************** @@ -174,7 +175,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page, clear_bit(MIDDLE_CHUNK_MAPPED, &page->private); clear_bit(NEEDS_COMPACTING, &page->private); clear_bit(PAGE_STALE, &page->private); - clear_bit(UNDER_RECLAIM, &page->private); + clear_bit(PAGE_CLAIMED, &page->private); spin_lock_init(&zhdr->page_lock); kref_init(&zhdr->refcount); @@ -223,8 +224,11 @@ static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud) unsigned long handle; handle = (unsigned long)zhdr; - if (bud != HEADLESS) - handle += (bud + zhdr->first_num) & BUDDY_MASK; + if (bud != HEADLESS) { + handle |= (bud + zhdr->first_num) & BUDDY_MASK; + if (bud == LAST) + handle |= (zhdr->last_chunks << BUDDY_SHIFT); + } return handle; } @@ -234,6 +238,12 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle) return (struct z3fold_header *)(handle & PAGE_MASK); } +/* only for LAST bud, returns zero otherwise */ +static unsigned short handle_to_chunks(unsigned long handle) +{ + return (handle & ~PAGE_MASK) >> BUDDY_SHIFT; +} + /* * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle * but that doesn't matter. because the masking will result in the @@ -717,37 +727,39 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle) page = virt_to_page(zhdr); if (test_bit(PAGE_HEADLESS, &page->private)) { - /* HEADLESS page stored */ - bud = HEADLESS; - } else { - z3fold_page_lock(zhdr); - bud = handle_to_buddy(handle); - - switch (bud) { - case FIRST: - zhdr->first_chunks = 0; - break; - case MIDDLE: - zhdr->middle_chunks = 0; - zhdr->start_middle = 0; - break; - case LAST: - zhdr->last_chunks = 0; - break; - default: - pr_err("%s: unknown bud %d\n", __func__, bud); - WARN_ON(1); - z3fold_page_unlock(zhdr); - return; + /* if a headless page is under reclaim, just leave. + * NB: we use test_and_set_bit for a reason: if the bit + * has not been set before, we release this page + * immediately so we don't care about its value any more. + */ + if (!test_and_set_bit(PAGE_CLAIMED, &page->private)) { + spin_lock(&pool->lock); + list_del(&page->lru); + spin_unlock(&pool->lock); + free_z3fold_page(page); + atomic64_dec(&pool->pages_nr); } + return; } - if (bud == HEADLESS) { - spin_lock(&pool->lock); - list_del(&page->lru); - spin_unlock(&pool->lock); - free_z3fold_page(page); - atomic64_dec(&pool->pages_nr); + /* Non-headless case */ + z3fold_page_lock(zhdr); + bud = handle_to_buddy(handle); + + switch (bud) { + case FIRST: + zhdr->first_chunks = 0; + break; + case MIDDLE: + zhdr->middle_chunks = 0; + break; + case LAST: + zhdr->last_chunks = 0; + break; + default: + pr_err("%s: unknown bud %d\n", __func__, bud); + WARN_ON(1); + z3fold_page_unlock(zhdr); return; } @@ -755,7 +767,7 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle) atomic64_dec(&pool->pages_nr); return; } - if (test_bit(UNDER_RECLAIM, &page->private)) { + if (test_bit(PAGE_CLAIMED, &page->private)) { z3fold_page_unlock(zhdr); return; } @@ -833,20 +845,30 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries) } list_for_each_prev(pos, &pool->lru) { page = list_entry(pos, struct page, lru); + + /* this bit could have been set by free, in which case + * we pass over to the next page in the pool. + */ + if (test_and_set_bit(PAGE_CLAIMED, &page->private)) + continue; + + zhdr = page_address(page); if (test_bit(PAGE_HEADLESS, &page->private)) - /* candidate found */ break; - zhdr = page_address(page); - if (!z3fold_page_trylock(zhdr)) + if (!z3fold_page_trylock(zhdr)) { + zhdr = NULL; continue; /* can't evict at this point */ + } kref_get(&zhdr->refcount); list_del_init(&zhdr->buddy); zhdr->cpu = -1; - set_bit(UNDER_RECLAIM, &page->private); break; } + if (!zhdr) + break; + list_del_init(&page->lru); spin_unlock(&pool->lock); @@ -895,6 +917,7 @@ next: if (test_bit(PAGE_HEADLESS, &page->private)) { if (ret == 0) { free_z3fold_page(page); + atomic64_dec(&pool->pages_nr); return 0; } spin_lock(&pool->lock); @@ -902,7 +925,7 @@ next: spin_unlock(&pool->lock); } else { z3fold_page_lock(zhdr); - clear_bit(UNDER_RECLAIM, &page->private); + clear_bit(PAGE_CLAIMED, &page->private); if (kref_put(&zhdr->refcount, release_z3fold_page_locked)) { atomic64_dec(&pool->pages_nr); @@ -961,7 +984,7 @@ static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle) set_bit(MIDDLE_CHUNK_MAPPED, &page->private); break; case LAST: - addr += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT); + addr += PAGE_SIZE - (handle_to_chunks(handle) << CHUNK_SHIFT); break; default: pr_err("unknown buddy id %d\n", buddy); -- 2.17.1