Message-ID: <20210928181357.rv47styhcp4ld5sb@kari-VirtualBox>
Date:   Tue, 28 Sep 2021 21:13:57 +0300
From:   Kari Argillander <kari.argillander@...il.com>
To:     Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
Cc:     ntfs3@...ts.linux.dev, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] fs/ntfs3: Remove locked argument in ntfs_set_ea

On Tue, Sep 28, 2021 at 09:01:38PM +0300, Konstantin Komarov wrote:
> 
> 
> On 27.09.2021 22:10, Kari Argillander wrote:
> > On Mon, Sep 27, 2021 at 06:10:00PM +0300, Konstantin Komarov wrote:
> >>
> >>
> >> On 25.09.2021 11:49, Kari Argillander wrote:
> >>> On Fri, Sep 24, 2021 at 07:15:50PM +0300, Konstantin Komarov wrote:
> >>>> We always need to lock now, because locks became smaller
> >>>> (see "Move ni_lock_dir and ni_unlock into ntfs_create_inode").
> >>>
> >>> So basically this actually fixes that commit?
> >>>
> >>> Fixes: d562e901f25d ("fs/ntfs3: Move ni_lock_dir and ni_unlock into ntfs_create_inode")
> >>>
> >>> Or if you do not use fixes atleast use
> >>>
> >>> d562e901f25d ("fs/ntfs3: Move ni_lock_dir and ni_unlock into ntfs_create_inode")
> >>>
> >>> You can add these to your gitconfig
> >>>
> >>> 	[core]
> >>> 		abbrev = 12
> >>> 	[pretty]
> >>> 	        fixes = Fixes: %h (\"%s\")
> >>> 		fixed = Fixes: %h (\"%s\")
> >>>
> >>> And get this annotation with
> >>> 	git show --pretty=fixes <sha>
> >>>
> >>> Have some comments below also.
> >>>
> >>>>
> >>>> Signed-off-by: Konstantin Komarov <almaz.alexandrovich@...agon-software.com>
> >>>> ---
> >>>>  fs/ntfs3/xattr.c | 28 +++++++++++++---------------
> >>>>  1 file changed, 13 insertions(+), 15 deletions(-)
> >>>>
> >>>> diff --git a/fs/ntfs3/xattr.c b/fs/ntfs3/xattr.c
> >>>> index 253a07d9aa7b..1ab109723b10 100644
> >>>> --- a/fs/ntfs3/xattr.c
> >>>> +++ b/fs/ntfs3/xattr.c
> >>>> @@ -257,7 +257,7 @@ static int ntfs_get_ea(struct inode *inode, const char *name, size_t name_len,
> >>>>  
> >>>>  static noinline int ntfs_set_ea(struct inode *inode, const char *name,
> >>>>  				size_t name_len, const void *value,
> >>>> -				size_t val_size, int flags, int locked)
> > 
> > Maybe we should leave int locked and ...
> > 
> >>>> +				size_t val_size, int flags)
> >>>>  {
> >>>>  	struct ntfs_inode *ni = ntfs_i(inode);
> >>>>  	struct ntfs_sb_info *sbi = ni->mi.sbi;
> >>>> @@ -276,8 +276,7 @@ static noinline int ntfs_set_ea(struct inode *inode, const char *name,
> >>>>  	u64 new_sz;
> >>>>  	void *p;
> >>>>  
> >>>> -	if (!locked)
> >>>> -		ni_lock(ni);
> >>>> +	ni_lock(ni);
> >>>>  
> >>>>  	run_init(&ea_run);
> >>>>  
> >>>> @@ -465,8 +464,7 @@ static noinline int ntfs_set_ea(struct inode *inode, const char *name,
> >>>>  	mark_inode_dirty(&ni->vfs_inode);
> >>>>  
> >>>>  out:
> >>>> -	if (!locked)
> >>>> -		ni_unlock(ni);
> >>>> +	ni_unlock(ni);
> >>>>  
> >>>>  	run_close(&ea_run);
> >>>>  	kfree(ea_all);
> >>>> @@ -537,7 +535,7 @@ struct posix_acl *ntfs_get_acl(struct inode *inode, int type)
> >>>>  
> >>>>  static noinline int ntfs_set_acl_ex(struct user_namespace *mnt_userns,
> >>>>  				    struct inode *inode, struct posix_acl *acl,
> >>>> -				    int type, int locked)
> >>>> +				    int type)
> >>>>  {
> >>>>  	const char *name;
> >>>>  	size_t size, name_len;
> >>>> @@ -594,7 +592,7 @@ static noinline int ntfs_set_acl_ex(struct user_namespace *mnt_userns,
> >>>>  		flags = 0;
> >>>>  	}
> >>>>  
> >>>> -	err = ntfs_set_ea(inode, name, name_len, value, size, flags, locked);
> >>>> +	err = ntfs_set_ea(inode, name, name_len, value, size, flags);
> >>>>  	if (err == -ENODATA && !size)
> >>>>  		err = 0; /* Removing non existed xattr. */
> >>>>  	if (!err)
> >>>> @@ -612,7 +610,7 @@ static noinline int ntfs_set_acl_ex(struct user_namespace *mnt_userns,
> >>>>  int ntfs_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
> >>>>  		 struct posix_acl *acl, int type)
> >>>>  {
> >>>> -	return ntfs_set_acl_ex(mnt_userns, inode, acl, type, 0);
> >>>> +	return ntfs_set_acl_ex(mnt_userns, inode, acl, type);
> >>>>  }
> >>>>  
> >>>>  static int ntfs_xattr_get_acl(struct user_namespace *mnt_userns,
> >>>> @@ -693,7 +691,7 @@ int ntfs_init_acl(struct user_namespace *mnt_userns, struct inode *inode,
> >>>>  
> >>>>  	if (default_acl) {
> >>>>  		err = ntfs_set_acl_ex(mnt_userns, inode, default_acl,
> >>>> -				      ACL_TYPE_DEFAULT, 1);
> >>>> +				      ACL_TYPE_DEFAULT);
> >>>>  		posix_acl_release(default_acl);
> >>>>  	} else {
> >>>>  		inode->i_default_acl = NULL;
> >>>> @@ -704,7 +702,7 @@ int ntfs_init_acl(struct user_namespace *mnt_userns, struct inode *inode,
> >>>>  	else {
> >>>>  		if (!err)
> >>>>  			err = ntfs_set_acl_ex(mnt_userns, inode, acl,
> >>>> -					      ACL_TYPE_ACCESS, 1);
> >>>> +					      ACL_TYPE_ACCESS);
> >>>>  		posix_acl_release(acl);
> >>>>  	}
> >>>>  
> >>>> @@ -988,7 +986,7 @@ static noinline int ntfs_setxattr(const struct xattr_handler *handler,
> >>>>  	}
> >>>>  #endif
> >>>>  	/* Deal with NTFS extended attribute. */
> >>>> -	err = ntfs_set_ea(inode, name, name_len, value, size, flags, 0);
> >>>> +	err = ntfs_set_ea(inode, name, name_len, value, size, flags);
> >>>>  
> >>>>  out:
> >>>>  	return err;
> >>>> @@ -1006,26 +1004,26 @@ int ntfs_save_wsl_perm(struct inode *inode)
> >>>>  
> > 
> > do lock here and ...
> > 
> >>>>  	value = cpu_to_le32(i_uid_read(inode));
> >>>>  	err = ntfs_set_ea(inode, "$LXUID", sizeof("$LXUID") - 1, &value,
> >>>> -			  sizeof(value), 0, 0);
> >>>> +			  sizeof(value), 0);
> >>>>  	if (err)
> >>>>  		goto out;
> >>>>  
> >>>>  	value = cpu_to_le32(i_gid_read(inode));
> >>>>  	err = ntfs_set_ea(inode, "$LXGID", sizeof("$LXGID") - 1, &value,
> >>>> -			  sizeof(value), 0, 0);
> >>>> +			  sizeof(value), 0);
> >>>>  	if (err)
> >>>>  		goto out;
> >>>>  
> >>>>  	value = cpu_to_le32(inode->i_mode);
> >>>>  	err = ntfs_set_ea(inode, "$LXMOD", sizeof("$LXMOD") - 1, &value,
> >>>> -			  sizeof(value), 0, 0);
> >>>> +			  sizeof(value), 0);
> >>>>  	if (err)
> >>>>  		goto out;
> >>>>  
> >>>>  	if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode)) {
> >>>>  		value = cpu_to_le32(inode->i_rdev);
> >>>>  		err = ntfs_set_ea(inode, "$LXDEV", sizeof("$LXDEV") - 1, &value,
> >>>> -				  sizeof(value), 0, 0);
> >>>> +				  sizeof(value), 0);
> > 
> > unlock here. Of course unlock also in error path.
> > 
> >>>
> >>> Is this really that we can lock/unlock same lock 4 times in a row in a
> >>> ntfs_set_ea? This does not feel correct. 
> >>>
> >>>   Argillander
> >>>
> >>
> >> How it was working before d562e901f25d 
> >> "fs/ntfs3: Move ni_lock_dir and ni_unlock into ntfs_create_inode":
> >>
> >> ntfs_create (lock mutex) =>
> >> ntfs_create_inode =>
> >> ntfs_save_wsl_perm (we are under lock here) =>
> >> return to ntfs_create and unlock
> >>
> >> How it works with d562e901f25d:
> >>
> >> ntfs_create => 
> >> ntfs_create_inode (lock in line 1201 file fs/ntfs3/inode.c 
> >> and unlock in line 1557) => 
> >> ntfs_save_wsl_perm (we aren't under lock here in line 1605)
> >>
> >> So we need to lock 4 times because there are 4 ntfs_set_ea calls.
> >> But now there can be done more work between those calls
> >> in other threads, locks became more granular.
> > 
> > Yeah but locking and locking 4 times when we can do it just ones is
> > quite waste. Please consider my suggestion above or tell what is wrong
> > with it. 
> > 
> >   Argillander
> > 
> 
> If I've understood correctly, you want to lock once in start of function 
> ntfs_save_wsl_perm and unlock at the end of it.
> It takes care of locks for those 4 calls to ntfs_set_ea.
> 
> But there are still other calls to ntfs_set_ea, that aren't protected
> in this case:
> function ntfs_set_acl_ex (line 603 file fs/ntfs3/xattr.c)
> err = ntfs_set_ea(inode, name, name_len, value, size, flags, locked);
> 
> This function called there:
> - function ntfs_set_acl  (line 621 file fs/ntfs3/xattr.c)
> return ntfs_set_acl_ex(mnt_userns, inode, acl, type);
> - function ntfs_init_acl (line 701 file fs/ntfs3/xattr.c)
> err = ntfs_set_acl_ex(mnt_userns, inode, default_acl,
> - function ntfs_init_acl (line 712 file fs/ntfs3/xattr.c)
> err = ntfs_set_acl_ex(mnt_userns, inode, acl,
> 
> So there are many entry points to ntfs_set_ea (and can be added more).
> Of course we can let int locked remain for these situations,
> but in my opinion it makes code a lot less readable
> (that was the reason to start looking into locking).

Yeah this what I was suggesting. And I totally agree that it is less
readable.

> I'm not sure, that winning some lock/unlocking
> in one specific scenario is worth it.

Still 4 locking / 4 unlocking in row is painfull. One option is to lock
outside of ntfs_set_acl if that is ok to you. If not maybe atleast add
todo comment to ntfs_set_wsl_perm that locking needs to be rethinked. I
know that there is lot of work to do with locks in here so maybe it is
not right time to nit pick about them.

> 
> >>
> >>>>  		if (err)
> >>>>  			goto out;
> >>>>  	}
> >>>> -- 
> >>>> 2.33.0
> >>>>
> >>>>

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