From: Dan Williams Subject: Re: [PATCH 2/2] ext4, dax: set ext4_dax_aops for dax files Date: Wed, 12 Sep 2018 09:41:42 -0700 Message-ID: References: <20180911154246.6844-1-toshi.kani@hpe.com> <20180911154246.6844-3-toshi.kani@hpe.com> <20180912093140.GB7782@quack2.suse.cz> <1f1cf9db3981390d2ad5a08d5f1987d9c933e687.camel@hpe.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: "jack@suse.cz" , "adilger.kernel@dilger.ca" , "linux-ext4@vger.kernel.org" , "linux-nvdimm@lists.01.org" , "linux-kernel@vger.kernel.org" , "tytso@mit.edu" To: "Kani, Toshi" Return-path: In-Reply-To: <1f1cf9db3981390d2ad5a08d5f1987d9c933e687.camel@hpe.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed, Sep 12, 2018 at 9:08 AM, Kani, Toshi wrote: > On Wed, 2018-09-12 at 11:31 +0200, Jan Kara wrote: >> On Tue 11-09-18 11:15:18, Dan Williams wrote: >> > On Tue, Sep 11, 2018 at 8:42 AM, Toshi Kani wrote: >> > > Sync syscall to an existing DAX file needs to flush processor cache, >> > > but it does not currently. This is because 'ext4_da_aops' is set to >> > > address_space_operations of existing DAX files, instead of 'ext4_dax_aops', >> > > since S_DAX flag is set after ext4_set_aops() in the open path. >> > > >> > > New file >> > > -------- >> > > lookup_open >> > > ext4_create >> > > __ext4_new_inode >> > > ext4_set_inode_flags // Set S_DAX flag >> > > ext4_set_aops // Set aops to ext4_dax_aops >> > > >> > > Existing file >> > > ------------- >> > > lookup_open >> > > ext4_lookup >> > > ext4_iget >> > > ext4_set_aops // Set aops to ext4_da_aops >> > > ext4_set_inode_flags // Set S_DAX flag >> > > >> > > Change ext4_iget() to call ext4_set_inode_flags() before ext4_set_aops(). >> > > >> > > Fixes: 5f0663bb4a64f588f0a2dd6d1be68d40f9af0086 >> > >> > Same format nit: >> > >> > Fixes: 5f0663bb4a64 ("ext4, dax: introduce ext4_dax_aops") >> > Cc: >> > >> > >> > > Signed-off-by: Toshi Kani >> > > Cc: Jan Kara >> > > Cc: Dan Williams >> > > Cc: "Theodore Ts'o" >> > > Cc: Andreas Dilger >> > > --- >> > > fs/ext4/inode.c | 3 ++- >> > > 1 file changed, 2 insertions(+), 1 deletion(-) >> > > >> > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> > > index 775cd9b4af55..93cbbb859c40 100644 >> > > --- a/fs/ext4/inode.c >> > > +++ b/fs/ext4/inode.c >> > > @@ -4998,6 +4998,8 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino) >> > > if (ret) >> > > goto bad_inode; >> > > >> > > + ext4_set_inode_flags(inode); >> > > + >> > >> > Hmm, does this have unintended behavior changes? >> > >> > I notice that there are some checks for flags "IS_APPEND(inode) || >> > IS_IMMUTABLE(inode)" *before* the call to ext4_set_inode_flags(). I >> > didn't look too much deeper at whether those checks are bogus, but it >> > would seem safer to do something like this for a lower risk fix. >> > >> > Thoughts? >> >> Well, safer but it would leave the landmine around for others to hit. >> Toshi, please move the ext4_set_inode_flags() call to be just after the >> assignment: >> >> ei->i_flags = le32_to_cpu(raw_inode->i_flags); >> >> in ext4_iget(). That way people won't introduce checks for i_flags that can >> never hit... And yes, it fixes also other bugs (mostly in sanity checks >> AFAICS) than the DAX issue. > > Sure. Assuming you think the implicit change Dan pointed out is not a > problem, yes, I will go with this cleaner approach. > Yes, Jan's proposal looks best to me.