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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 190-20020a250ac7000000b00b7767ca749esm2605415ybk.59.2023.04.23.19.17.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 23 Apr 2023 19:17:20 -0700 (PDT) Date: Sun, 23 Apr 2023 19:17:12 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: David Stevens cc: Hugh Dickins , Andrew Morton , Ivan Orlov , Jiaqi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH next] mm/khugepaged: fix conflicting mods to collapse_file() In-Reply-To: Message-ID: References: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="-1463760895-436720276-1682302640=:4090" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8D02B120007 X-Rspam-User: X-Stat-Signature: 9wc7imogy6fj1di4u9ggtcc7b6u3g5n9 X-HE-Tag: 1682302642-160583 X-HE-Meta: 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 1da7L9Cl 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 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: This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---1463760895-436720276-1682302640=:4090 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE On Mon, 24 Apr 2023, David Stevens wrote: > On Sun, Apr 23, 2023 at 1:47=E2=80=AFPM Hugh Dickins w= rote: > > > > Inserting Ivan Orlov's syzbot fix commit 2ce0bdfebc74 > > ("mm: khugepaged: fix kernel BUG in hpage_collapse_scan_file()") > > ahead of Jiaqi Yan's and David Stevens's commits > > 12904d953364 ("mm/khugepaged: recover from poisoned file-backed memory"= ) > > cae106dd67b9 ("mm/khugepaged: refactor collapse_file control flow") > > ac492b9c70ca ("mm/khugepaged: skip shmem with userfaultfd") > > (all of which restructure collapse_file()) did not work out well. > > > > xfstests generic/086 on huge tmpfs (with accelerated khugepaged) freeze= s > > (if not on the first attempt, then the 2nd or 3rd) in find_lock_entries= () > > while doing drop_caches: the file's xarray seems to have been corrupted= , > > with find_get_entry() returning nonsense which makes no progress. > > > > Bisection led to ac492b9c70ca; and diff against earlier working linux-n= ext > > suggested that it's probably down to an errant xas_store(), which does = not > > belong with the later changes (and nor does the positioning of warnings= ). > > The later changes look as if they fix the syzbot issue independently. > > > > Remove most of what's left of 2ce0bdfebc74: just leave one WARN_ON_ONCE > > (xas_error) after the final xas_store() of the multi-index entry. > > > > Signed-off-by: Hugh Dickins > > --- > > > > mm/khugepaged.c | 23 +---------------------- > > 1 file changed, 1 insertion(+), 22 deletions(-) > > > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -1941,16 +1941,6 @@ static int collapse_file(struct mm_struct *mm, u= nsigned long addr, > > result =3D SCAN_FAIL; > > goto xa_locked; > > } > > - xas_store(&xas, hpage); > > - if (xas_error(&xas)) { > > - /* revert shmem_charge performe= d > > - * in the previous condition > > - */ > > - mapping->nrpages--; > > - shmem_uncharge(mapping->host, 1= ); > > - result =3D SCAN_STORE_FAILED; >=20 > With this being removed, SCAN_STORE_FAILED should also be removed from > the scan_result enum and trace event definitions. Only if we also remove your use of SCAN_STORE_FAILED in ac492b9c70ca: what would you want that to say instead? I don't care myself for any of those "SCAN" result codes, nor whether they are few or many: I'd rather have __LINE__ numbers for my own debugging. But if people want to remove SCAN_STORE_FAILED now, sure, send a patch; my intent was to unbreak the breakage. Hugh ---1463760895-436720276-1682302640=:4090--