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=-8.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 40BC8C433E0 for ; Fri, 5 Feb 2021 17:44:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AB57264DD9 for ; Fri, 5 Feb 2021 17:44:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AB57264DD9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 223066B0074; Fri, 5 Feb 2021 12:44:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1AF776B0075; Fri, 5 Feb 2021 12:44:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 075926B0078; Fri, 5 Feb 2021 12:44:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0211.hostedemail.com [216.40.44.211]) by kanga.kvack.org (Postfix) with ESMTP id DFE4D6B0074 for ; Fri, 5 Feb 2021 12:44:40 -0500 (EST) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id A9A6F181AEF1E for ; Fri, 5 Feb 2021 17:44:40 +0000 (UTC) X-FDA: 77784939120.12.bun84_1f0bea9275e6 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 85E5E18028B73 for ; Fri, 5 Feb 2021 17:44:40 +0000 (UTC) X-HE-Tag: bun84_1f0bea9275e6 X-Filterd-Recvd-Size: 7591 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf29.hostedemail.com (Postfix) with ESMTP for ; Fri, 5 Feb 2021 17:44:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=WTOYkO8xgxh6+cxoqHMXLP73u+ngAcUFQvBQ799Oj4I=; b=RSNnrU0eDb+nkyop/RJYh1yq1s peyU7BTzC9ITvPQQBDL31Tke2qqMDigbOuL5WKhxq8DF8ON1BYvGea5/Np8jHXuCw8HxTJ43ULF2l mm+kXn+Ro148GTzgf4gliQYYH5YIFIRSvluiOaliXxgTQ4OZmy3h73oQkmBvsaBFM4dvBnnca5IE2 QXIWD2K2otw7bj+BVJW7/Bvf7+7B2I9R/Yqo6wmiHIOJQu6WJfSDRrc6CAMFZsT0M4Kv2nWyPnpfE 85dF3V/C5CcL98iS5eM7sSCwoJsO1xeKsXrjtJsfnVROy07cqYB3Rq4/M14oBX6rlH+41U5nHE59L zmEMsTrA==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1l859l-002aCD-0l; Fri, 05 Feb 2021 17:44:33 +0000 Date: Fri, 5 Feb 2021 17:44:33 +0000 From: Matthew Wilcox To: Hugh Dickins Cc: Andrew Morton , syzbot , linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, Alex Shi , Roman Gushchin , Wu Fengguang Subject: Re: INFO: task can't die in shrink_inactive_list (2) Message-ID: <20210205174433.GJ308988@casper.infradead.org> References: <0000000000000340a105b49441d3@google.com> <20201123195452.8ecd01b1fc2ce287dfd6a0d5@linux-foundation.org> <20201221203344.GG874@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201221203344.GG874@casper.infradead.org> 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: Hugh, did you get a chance to test this? On Mon, Dec 21, 2020 at 08:33:44PM +0000, Matthew Wilcox wrote: > On Mon, Dec 21, 2020 at 11:56:36AM -0800, Hugh Dickins wrote: > > On Mon, 23 Nov 2020, Andrew Morton wrote: > > > On Fri, 20 Nov 2020 17:55:22 -0800 syzbot wrote: > > > > > > > Hello, > > > > > > > > syzbot found the following issue on: > > > > > > > > HEAD commit: 03430750 Add linux-next specific files for 20201116 > > > > git tree: linux-next > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=13f80e5e500000 > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=a1c4c3f27041fdb8 > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=e5a33e700b1dd0da20a2 > > > > compiler: gcc (GCC) 10.1.0-syz 20200507 > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12f7bc5a500000 > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10934cf2500000 > > > > > > Alex, your series "per memcg lru lock" changed the vmscan code rather a > > > lot. Could you please take a look at that reproducer? > > > > Andrew, I promised I'd take a look at this syzreport too (though I think > > we're agreed by now that it has nothing to do with per-memcg lru_lock). > > > > I did try, but (unlike Alex) did not manage to get the reproducer to > > reproduce it. No doubt I did not try hard enough: I did rather lose > > interest after seeing that it appears to involve someone with > > CAP_SYS_ADMIN doing an absurdly large ioctl(BLKFRASET) on /dev/nullb0 > > ("Null test block driver" enabled via CONFIG_BLK_DEV_NULL_BLK=y: that I > > did enable) and faulting from it: presumably triggering an absurd amount > > of readahead. > > > > Cc'ing Matthew since he has a particular interest in readahead, and > > might be inspired to make some small safe change that would fix this, > > and benefit realistic cases too; but on the whole it didn't look worth > > worrying about - or at least not by me. > > Oh, interesting. Thanks for looping me in, I hadn't looked at this one > at all. Building on the debugging you did, this is the interesting > part of the backtrace to me: > > > > > try_to_free_pages+0x29f/0x720 mm/vmscan.c:3264 > > > > __perform_reclaim mm/page_alloc.c:4360 [inline] > > > > __alloc_pages_direct_reclaim mm/page_alloc.c:4381 [inline] > > > > __alloc_pages_slowpath.constprop.0+0x917/0x2510 mm/page_alloc.c:4785 > > > > __alloc_pages_nodemask+0x5f0/0x730 mm/page_alloc.c:4995 > > > > alloc_pages_current+0x191/0x2a0 mm/mempolicy.c:2271 > > > > alloc_pages include/linux/gfp.h:547 [inline] > > > > __page_cache_alloc mm/filemap.c:977 [inline] > > > > __page_cache_alloc+0x2ce/0x360 mm/filemap.c:962 > > > > page_cache_ra_unbounded+0x3a1/0x920 mm/readahead.c:216 > > > > do_page_cache_ra+0xf9/0x140 mm/readahead.c:267 > > > > do_sync_mmap_readahead mm/filemap.c:2721 [inline] > > > > filemap_fault+0x19d0/0x2940 mm/filemap.c:2809 > > So ra_pages has been set to something ridiculously large, and as > a result, we call do_page_cache_ra() asking to read more memory than > is available in the machine. Funny thing, we actually have a function > to prevent this kind of situation, and it's force_page_cache_ra(). > > So this might fix the problem. I only tested that it compiles. I'll > be happy to write up a proper changelog and sign-off for it if it works ... > it'd be good to get it some soak testing on a variety of different > workloads; changing this stuff is enormously subtle. > > As a testament to that, I think Fengguang got it wrong in commit > 2cbea1d3ab11 -- async_size should have been 3 * ra_pages / 4, not ra_pages > / 4 (because we read-behind by half the range, so we're looking for a > page fault to happen a quarter of the way behind this fault ...) > > This is partially Roman's fault, see commit 600e19afc5f8. > > diff --git a/mm/filemap.c b/mm/filemap.c > index d5e7c2029d16..43fe0f0ae3bb 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2632,7 +2632,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > ra->size = ra->ra_pages; > ra->async_size = ra->ra_pages / 4; > ractl._index = ra->start; > - do_page_cache_ra(&ractl, ra->size, ra->async_size); > + force_page_cache_ra(&ractl, ra, ra->size); > return fpin; > } > > diff --git a/mm/internal.h b/mm/internal.h > index c43ccdddb0f6..5664b4b91340 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -49,8 +49,6 @@ void unmap_page_range(struct mmu_gather *tlb, > unsigned long addr, unsigned long end, > struct zap_details *details); > > -void do_page_cache_ra(struct readahead_control *, unsigned long nr_to_read, > - unsigned long lookahead_size); > void force_page_cache_ra(struct readahead_control *, struct file_ra_state *, > unsigned long nr); > static inline void force_page_cache_readahead(struct address_space *mapping, > diff --git a/mm/readahead.c b/mm/readahead.c > index c5b0457415be..f344c894c26a 100644 > --- a/mm/readahead.c > +++ b/mm/readahead.c > @@ -246,7 +246,7 @@ EXPORT_SYMBOL_GPL(page_cache_ra_unbounded); > * behaviour which would occur if page allocations are causing VM writeback. > * We really don't want to intermingle reads and writes like that. > */ > -void do_page_cache_ra(struct readahead_control *ractl, > +static void do_page_cache_ra(struct readahead_control *ractl, > unsigned long nr_to_read, unsigned long lookahead_size) > { > struct inode *inode = ractl->mapping->host; >