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by smtp.kernel.org (Postfix) with ESMTPSA id 2C742C4CED1; Mon, 10 Feb 2025 18:58:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739213936; bh=ACE/dkbUZ1XUCycn18S094uP4VYPF9omfbNKrW5W5N0=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=MMk5rQFzVvRPs3sbliT7PBNCGcBVQnwtyQBSHghSYIzAaJpZfcGE35Zwz3rWTltru eHx0DsbPKzz8Qbju/ZynGkjGR7fvRoOM6l8yNl/o3Y0qfK089iM9AqgPRgUWSPwY2h GwTajbztsoEg/Ix+TLf3YHnBBFliQLFPZPkNmlFwp9UTJkv5fdDDkXRtV2TZRCdBpi od2n/SVtMdJFQAisN+X3Z0fldvoO8TDgEWjxg1tuMqK+LIETCdBq4XJmI61U1Yz17b DtjtlHMiVgoh4sy1JToEMuNypLAIu4cPlBkaE1WkKp5nafjrurrRe2xSbMUDYqfGyl phWKx4xdxjPKQ== Message-ID: <169e0d9e3b1e4ab5fd84e41817a1aeb76c08851e.camel@kernel.org> Subject: Re: [REGRESSION][BISECTED] Crash with Bad page state for FUSE/Flatpak related applications since v6.13 From: Jeff Layton To: Vlastimil Babka , Joanne Koong , Matthew Wilcox Cc: Josef Bacik , Miklos Szeredi , Christian Heusel , Miklos Szeredi , regressions@lists.linux.dev, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm , Mantas =?UTF-8?Q?Mikul=C4=97nas?= Date: Mon, 10 Feb 2025 13:58:54 -0500 In-Reply-To: <81298bd1-e630-4940-ae5b-7882576b6bf4@suse.cz> References: <2f681f48-00f5-4e09-8431-2b3dbfaa881e@heusel.eu> <9cd88643-daa8-4379-be0a-bd31de277658@suse.cz> <20250207172917.GA2072771@perftesting> <8f7333f2-1ba9-4df4-bc54-44fd768b3d5b@suse.cz> <81298bd1-e630-4940-ae5b-7882576b6bf4@suse.cz> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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 5WX8EZWP OLJleqZkXQG2A8kukXCcm2nTqJfQb3lwFNEjSN8DVW+SZjYyKOM0k8caKlLCawL07G5kP/iypuMdmjrJDSonKpYNl9htuBqK0OfjRcjMRcuhEs0ESGbFbyjU+2K5oc7+A87DhhyQ10LRotiF6+VyCQuarUO0X58Y35ZDUtoD339wN+RHskUMC+XUUZHD5c4Z9zrNSefLt5S5DhfAnELWHBpze6pkCgfc7XLOOrvmMI1P30Hi9n4eMWJfXQ2wK65h/5M0tfajVIVfRHEbdZ8FERO2IaR27PUt7OLyHWAIkr7zal2CNKUFkjew6wQ== 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: List-Subscribe: List-Unsubscribe: On Mon, 2025-02-10 at 09:27 +0100, Vlastimil Babka wrote: > On 2/8/25 16:46, Joanne Koong wrote: > > On Sat, Feb 8, 2025 at 2:11=E2=80=AFAM Matthew Wilcox wrote: > > >=20 > > > On Fri, Feb 07, 2025 at 04:22:56PM -0800, Joanne Koong wrote: > > > > > Thanks, Josef. I guess we can at least try to confirm we're on th= e right track. > > > > > Can anyone affected see if this (only compile tested) patch fixes= the issue? > > > > > Created on top of 6.13.1. > > > >=20 > > > > This fixes the crash for me on 6.14.0-rc1. I ran the repro using > > > > Mantas's instructions for Obfuscate. I was able to trigger the cras= h > > > > on a clean build and then with this patch, I'm not seeing the crash > > > > anymore. > > >=20 > > > Since this patch fixes the bug, we're looking for one call to folio_p= ut() > > > too many. Is it possibly in fuse_try_move_page()? In particular, th= is > > > one: > > >=20 > > > /* Drop ref for ap->pages[] array */ > > > folio_put(oldfolio); > > >=20 > > > I don't know fuse very well. Maybe this isn't it. > >=20 > > Yeah, this looks it to me. We don't grab a folio reference for the > > ap->pages[] array for readahead and it tracks with Mantas's > > fuse_dev_splice_write() dmesg. this patch fixed the crash for me when > > I tested it yesterday: > >=20 > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > > index 7d92a5479998..172cab8e2caf 100644 > > --- a/fs/fuse/file.c > > +++ b/fs/fuse/file.c > > @@ -955,8 +955,10 @@ static void fuse_readpages_end(struct fuse_mount > > *fm, struct fuse_args *args, > > fuse_invalidate_atime(inode); > > } > >=20 > > - for (i =3D 0; i < ap->num_folios; i++) > > + for (i =3D 0; i < ap->num_folios; i++) { > > folio_end_read(ap->folios[i], !err); > > + folio_put(ap->folios[i]); > > + } > > if (ia->ff) > > fuse_file_put(ia->ff, false); > >=20 > > @@ -1049,6 +1051,7 @@ static void fuse_readahead(struct readahead_contr= ol *rac) > >=20 > > while (ap->num_folios < cur_pages) { > > folio =3D readahead_folio(rac); > > + folio_get(folio); >=20 > This is almost the same as my patch, but balances the folio_put() in > readahead_folio() with another folio_get(), while mine uses > __readahead_folio() that does not do folio_put() in the first place. >=20 > But I think neither patch proves the extraneous folio_put() comes from > fuse_try_move_page(). >=20 > > ap->folios[ap->num_folios] =3D folio; > > ap->descs[ap->num_folios].length =3D folio_size= (folio); > > ap->num_folios++; > >=20 > >=20 > > I reran it just now with a printk by that ref drop in > > fuse_try_move_page() and I'm indeed seeing that path get hit. >=20 > It might get hit, but is it hit in the readahead paths? One way to test > would be to instead of yours above or mine change, to stop doing the > foio_put() in fuse_try_move_page(). But maybe it's called also from other > contexts that do expect it, and will leak memory otherwise. >=20 I think you're right that there is a double put in fuse_try_move_page(). Let's assume that we enter that function and the refcount on "oldpage" is 1: 1/ We take a reference to "oldfolio" when we enter the function, now refcount is 2. 2/ We drop a reference on "oldfolio" with the call to replace_page_cache_folio. Now refcount is 1. 3/ Now there are 2 folio_put(oldfolio) calls on the way out of the function, refcount goes to -1. Maybe it's expected that this function consumes an extra folio reference, but it's certainly not evident why that is if so. I don't see why the callers would expect that either. > > Not sure why fstests didn't pick this up though since splice is > > enabled by default in passthrough_hp, i'll look into this next week. > >=20 >=20 >=20 --=20 Jeff Layton