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Fri, 17 May 2024 01:17:24 +0200 Message-ID: Date: Fri, 17 May 2024 08:47:20 +0930 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] btrfs: always set an inode's delayed_inode with WRITE_ONCE() To: fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNIlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT7CwJQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCY00iVQUJDToH pgAKCRDCPZHzoSX+qNKACACkjDLzCvcFuDlgqCiS4ajHAo6twGra3uGgY2klo3S4JespWifr BLPPak74oOShqNZ8yWzB1Bkz1u93Ifx3c3H0r2vLWrImoP5eQdymVqMWmDAq+sV1Koyt8gXQ XPD2jQCrfR9nUuV1F3Z4Lgo+6I5LjuXBVEayFdz/VYK63+YLEAlSowCF72Lkz06TmaI0XMyj jgRNGM2MRgfxbprCcsgUypaDfmhY2nrhIzPUICURfp9t/65+/PLlV4nYs+DtSwPyNjkPX72+ LdyIdY+BqS8cZbPG5spCyJIlZonADojLDYQq4QnufARU51zyVjzTXMg5gAttDZwTH+8LbNI4 mm2YzsBNBFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcga CbPEwhLj1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj /IrRUUka68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fN GSsRb+pKEKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0 q1eW4Jrv0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEv ABEBAAHCwHwEGAEIACYCGwwWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCY00ibgUJDToHvwAK CRDCPZHzoSX+qK6vB/9yyZlsS+ijtsvwYDjGA2WhVhN07Xa5SBBvGCAycyGGzSMkOJcOtUUf tD+ADyrLbLuVSfRN1ke738UojphwkSFj4t9scG5A+U8GgOZtrlYOsY2+cG3R5vjoXUgXMP37 INfWh0KbJodf0G48xouesn08cbfUdlphSMXujCA8y5TcNyRuNv2q5Nizl8sKhUZzh4BascoK DChBuznBsucCTAGrwPgG4/ul6HnWE8DipMKvkV9ob1xJS2W4WJRPp6QdVrBWJ9cCdtpR6GbL iQi22uZXoSPv/0oUrGU+U5X4IvdnvT+8viPzszL5wXswJZfqfy8tmHM85yjObVdIG6AlnrrD In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:TPVIxzUj8PGQAVFysajgEH5wc3e079oTGkiDJ8ZqLeQqBKao+gm BRjI68ncZtYhNDEzW8jyn6wU5sX1XOckZnYEMVnrmTFTSWEqhsRPBttLu/UM4YmyTxFPt2D Git45PDTWasctieZxTZwDrZCzoY+6uSuiNxWjQXQNS8sjUYPM3gULO4UJ3eL8sDx0l9vo55 ovx7+JkNT1Z0H9eT3A2ZQ== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:P0DwFGQKNNo=;a8XszxuMNocA/r3NnAQ87a68X5j 17mYnCRoBUTQCW9qKb5wtmZrRPG0R0SeEoVYAx2X2LFDzJaToAVFwt+XYy8bxe5MZKPDpBaWH 2dlCtamlmi/9Of32N5a8JEPBTuoCMjWbKlzxThbJkreGPHol+XQPf4IOioyGK8up0SLnr+WRR VZcsSppBhgPv086mc5ocMrHowuywDAFO8yYn+ADVmfuVgJd8NjVGEtAJaSyEjoMKPgA6CnylT 2YUq/cbnt3biEfQdHp8t0kqBvOtP6rvTe2bGgy0wJm8MD7y3HoSdcJIs/QFL5nShN6LDddYji zL/CDxYRquJBJru6kMKkG5tDiOMA8/HwKUQZ8fIJ2QLZKXNu5MFVBUaPQAB1EklSyIFLsyDWl As6YPpi2wF3FQo/VmbavH3bJGZugL4fP5kFZ/U6n4Bgw5B3IqEKyDWRABUL9eLgabWNO+gkJp 2BLUs8oqO3HqEbd4vNSjmyGVD9tmn4a7CVZyKCopwB7V4oDQ9JZuhd8mQ42z7zC91JQNyoh7J mMAva3ZEQfH8dIUXOAJ2wyLs2bQTJVatv8mViALrkfdhcDcC19vsmyPjuFWof1mJ68WiWuc+9 BTVbTg/3cVunEkr7rHYGtaYEu+ucfx3VpfBiuSVB/yMihRZ3DoK/ecmu52ofOCW2pCytSISoQ NNpw0bH9NIKWxzmyVuMAoBeS1c7DuBfCEYY3czqRcPqUOPotMU+elNhIVgfijM8WjD30VU1w1 RVFsqTCnn+eiBPbMoZWK16xTgHb1qfuoD21WOfnYusUtryYdkIpH9q5arMBNT2ynonk5p5gPO wOcNtXB/utofgctqSoQ4gW8v1WcfmBUlaU4cHpZ82NxT0= =E5=9C=A8 2024/5/17 00:58, fdmanana@kernel.org =E5=86=99=E9=81=93: > From: Filipe Manana > > Currently we have a couple places using READ_ONCE() to access an inode's > delayed_inode without taking the lock that protects the xarray for delay= ed > inodes, while all the other places access it while holding the lock. > > However we never update the delayed_inode pointer of an inode with > WRITE_ONCE(), making the use of READ_ONCE() pointless since it should > always be paired with a WRITE_ONCE() in order to protect against issues > such as write tearing for example. > > So change all the places that update struct btrfs_inode::delayed_inode t= o > use WRITE_ONCE() instead of simple assignments. > > Signed-off-by: Filipe Manana A quick search shows that we still have one call site not using READ_ONCE(= ): Inside btrfs_dirty_inode() of inode.c we have btrfs_end_transaction(trans); if (inode->delayed_inode) btrfs_balance_delayed_items(fs_info); I guess we should also use READ_ONCE() for it? Thanks, Qu > --- > fs/btrfs/delayed-inode.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c > index 483c141dc488..6df7e44d9d31 100644 > --- a/fs/btrfs/delayed-inode.c > +++ b/fs/btrfs/delayed-inode.c > @@ -106,7 +106,7 @@ static struct btrfs_delayed_node *btrfs_get_delayed_= node( > */ > if (refcount_inc_not_zero(&node->refs)) { > refcount_inc(&node->refs); > - btrfs_inode->delayed_node =3D node; > + WRITE_ONCE(btrfs_inode->delayed_node, node); > } else { > node =3D NULL; > } > @@ -161,7 +161,7 @@ static struct btrfs_delayed_node *btrfs_get_or_creat= e_delayed_node( > ASSERT(xa_err(ptr) !=3D -EINVAL); > ASSERT(xa_err(ptr) !=3D -ENOMEM); > ASSERT(ptr =3D=3D NULL); > - btrfs_inode->delayed_node =3D node; > + WRITE_ONCE(btrfs_inode->delayed_node, node); > xa_unlock(&root->delayed_nodes); > > return node; > @@ -1312,7 +1312,7 @@ void btrfs_remove_delayed_node(struct btrfs_inode = *inode) > if (!delayed_node) > return; > > - inode->delayed_node =3D NULL; > + WRITE_ONCE(inode->delayed_node, NULL); > btrfs_release_delayed_node(delayed_node); > } >