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> --- 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
