On Tue 11-06-24 06:15:40, Mateusz Guzik wrote: > new_inode used to have the following: > spin_lock(&inode_lock); > inodes_stat.nr_inodes++; > list_add(&inode->i_list, &inode_in_use); > list_add(&inode->i_sb_list, &sb->s_inodes); > inode->i_ino = ++last_ino; > inode->i_state = 0; > spin_unlock(&inode_lock); > > over time things disappeared, got moved around or got replaced (global > inode lock with a per-inode lock), eventually this got reduced to: > spin_lock(&inode->i_lock); > inode->i_state = 0; > spin_unlock(&inode->i_lock); > > But the lock acquire here does not synchronize against anyone. > > Additionally iget5_locked performs i_state = 0 assignment without any > locks to begin with and the two combined look confusing at best. > > It looks like the current state is a leftover which was not cleaned up. > > Ideally it would be an invariant that i_state == 0 to begin with, but > achieving that would require dealing with all filesystem alloc handlers > one by one. > > In the meantime drop the misleading locking and move i_state zeroing to > alloc_inode so that others don't need to deal with it by hand. > > Signed-off-by: Mateusz Guzik <mjguzik@xxxxxxxxx> Good point. But the initialization would seem more natural in inode_init_always(), wouldn't it? And that will also address your "FIXME" comment. Honza > --- > > I diffed this against fs-next + my inode hash patch as it adds one > i_state = 0 case. Should that patch not be accepted this bit can be > easily dropped from this one. > > I brought the entire thing up quite some time ago [1] and Dave Chinner > noted that perhaps the lock has a side effect of providing memory > barriers which otherwise would not be there and which are needed by > someone. > > For new_inode and alloc_inode consumers all fences are already there > anyway due to immediate lock usage. > > Arguably new_inode_pseudo escape without it but I don't find the code at > hand to be affected in any meanignful way -- the only 2 consumers > (get_pipe_inode and sock_alloc) perform numerous other stores to the > inode immediately after. By the time it gets added to anything looking > at i_state, flushing that should be handled by whatever thing which adds > it. Mentioning this just in case. > > [1] https://lore.kernel.org/all/CAGudoHF_Y0shcU+AMRRdN5RQgs9L_HHvBH8D4K=7_0X72kYy2g@xxxxxxxxxxxxxx/ > > fs/inode.c | 15 +++++---------- > 1 file changed, 5 insertions(+), 10 deletions(-) > > diff --git a/fs/inode.c b/fs/inode.c > index 149adf8ab0ea..3967e68311a6 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -276,6 +276,10 @@ static struct inode *alloc_inode(struct super_block *sb) > return NULL; > } > > + /* > + * FIXME: the code should be able to assert i_state == 0 instead. > + */ > + inode->i_state = 0; > return inode; > } > > @@ -1023,14 +1027,7 @@ EXPORT_SYMBOL(get_next_ino); > */ > struct inode *new_inode_pseudo(struct super_block *sb) > { > - struct inode *inode = alloc_inode(sb); > - > - if (inode) { > - spin_lock(&inode->i_lock); > - inode->i_state = 0; > - spin_unlock(&inode->i_lock); > - } > - return inode; > + return alloc_inode(sb); > } > > /** > @@ -1254,7 +1251,6 @@ struct inode *iget5_locked(struct super_block *sb, unsigned long hashval, > struct inode *new = alloc_inode(sb); > > if (new) { > - new->i_state = 0; > inode = inode_insert5(new, hashval, test, set, data); > if (unlikely(inode != new)) > destroy_inode(new); > @@ -1297,7 +1293,6 @@ struct inode *iget5_locked_rcu(struct super_block *sb, unsigned long hashval, > > new = alloc_inode(sb); > if (new) { > - new->i_state = 0; > inode = inode_insert5(new, hashval, test, set, data); > if (unlikely(inode != new)) > destroy_inode(new); > -- > 2.43.0 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
