From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1454336914.133285.297.camel@infradead.org> Subject: Re: JFFS2 deadlock From: David Woodhouse To: Thomas.Betker@rohde-schwarz.com, computersforpeace@gmail.com Cc: linux-mtd , Artem Bityutskiy , Thomas Betker , linux-kernel@vger.kernel.org, Joakim Tjernlund , "sztomi89@gmail.com" , wangzaiwei , "linux-mtd@lists.infradead.org" , Alexander Viro , Ming Liu , linux-fsdevel@vger.kernel.org, Deng Chao Date: Mon, 01 Feb 2016 14:28:34 +0000 In-Reply-To: References: <1453910781.20662.35.camel@infinera.com> <20160128000559.GA14270@google.com> Content-Type: multipart/signed; micalg="sha-1"; protocol="application/x-pkcs7-signature"; boundary="=-ipUDn6a8buH5NGFubErP" Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: --=-ipUDn6a8buH5NGFubErP Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2016-01-28 at 09:16 +0100, Thomas.Betker@rohde-schwarz.com wrote: >=20 > Subject: [PATCH] Revert "jffs2: Fix lock acquisition order bug in=C2=A0 > jffs2_write_begin" > http://article.gmane.org/gmane.linux.drivers.mtd/62951 >=20 > This is a patch revising my original patch, which I sent to linux-mtd on= =C2=A0 > 10-Nov-2015. I didn't see a response yet, but it's one of the outstanding= =C2=A0 > patches above. That looks necessary but not sufficient. I think we need this (untested) patch on top of it, to ensure that we *always* take the page lock before f->sem? Please could you try what's in the tree at http://git.infradead.org/users/dwmw2/jffs2-fixes.git ---- From: David Woodhouse Subject: [PATCH] jffs2: Fix page lock / f->sem deadlock With this fix, all code paths should now be obtaining the page lock before f->sem. Reported-by: Szab=C3=B3 Tam=C3=A1s Reported-by: Thomas Betker Signed-off-by: David Woodhouse Cc: stable@vger.kernel.org --- =C2=A0fs/jffs2/README.Locking |=C2=A0=C2=A05 +---- =C2=A0fs/jffs2/gc.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0| 17 ++++++++++------- =C2=A02 files changed, 11 insertions(+), 11 deletions(-) diff --git a/fs/jffs2/README.Locking b/fs/jffs2/README.Locking index 3ea3655..8918ac9 100644 --- a/fs/jffs2/README.Locking +++ b/fs/jffs2/README.Locking @@ -2,10 +2,6 @@ =C2=A0 JFFS2 LOCKING DOCUMENTATION =C2=A0 --------------------------- =C2=A0 -At least theoretically, JFFS2 does not require the Big Kernel Lock -(BKL), which was always helpfully obtained for it by Linux 2.4 VFS -code. It has its own locking, as described below. - =C2=A0This document attempts to describe the existing locking rules for =C2=A0JFFS2. It is not expected to remain perfectly up to date, but ought t= o =C2=A0be fairly close. @@ -69,6 +65,7 @@ Ordering constraints: =C2=A0 =C2=A0=C2=A0=C2=A0any f->sem held. =C2=A0 2. Never attempt to lock two file mutexes in one thread. =C2=A0 =C2=A0=C2=A0=C2=A0No ordering rules have been made for doing so. + 3. Never lock a page cache page with f->sem held. =C2=A0 =C2=A0 =C2=A0 erase_completion_lock spinlock diff --git a/fs/jffs2/gc.c b/fs/jffs2/gc.c index 6fb0802..5919fef 100644 --- a/fs/jffs2/gc.c +++ b/fs/jffs2/gc.c @@ -1316,14 +1316,17 @@ static int jffs2_garbage_collect_dnode(struct jffs2= _sb_info *c, struct jffs2_era =C2=A0 BUG_ON(start > orig_start); =C2=A0 } =C2=A0 - /* First, use readpage() to read the appropriate page into the page cache= */ - /* Q: What happens if we actually try to GC the _same_ page for which com= mit_write() - =C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0triggered garbage collection in the first = place? - =C2=A0* A: I _think_ it's OK. read_cache_page shouldn't deadlock, we'll w= rite out the - =C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0page OK. We'll actually write it out again= in commit_write, which is a little - =C2=A0*=C2=A0=C2=A0=C2=A0=C2=A0suboptimal, but at least we're correct. - =C2=A0*/ + /* The rules state that we must obtain the page lock *before* f->sem, so + =C2=A0* drop f->sem temporarily. Since we also hold c->alloc_sem, nothing= 's + =C2=A0* actually going to *change* so we're safe; we only allow reading. + =C2=A0* + =C2=A0* It is important to note that jffs2_write_begin() will ensure that= its + =C2=A0* page is marked Uptodate before allocating space. That means that = if we + =C2=A0* end up here trying to GC the *same* page that jffs2_write_begin()= is + =C2=A0* trying to write out, read_cache_page() will not deadlock. */ + mutex_unlock(&f->sem); =C2=A0 pg_ptr =3D jffs2_gc_fetch_page(c, f, start, &pg); + mutex_lock(&f->sem); =C2=A0 =C2=A0 if (IS_ERR(pg_ptr)) { =C2=A0 pr_warn("read_cache_page() returned error: %ld\n", --=C2=A0 2.5.0 --=20 David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation --=-ipUDn6a8buH5NGFubErP Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIISjjCCBicw ggUPoAMCAQICAw3vNzANBgkqhkiG9w0BAQUFADCBjDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0 YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcx ODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNzIDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENB 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