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kernfs: dont take i_lock on inode attr read 

The kernfs write lock is held when the kernfs node inode attributes
are updated. Therefore, when either kernfs_iop_getattr() or
kernfs_iop_permission() are called the kernfs node inode attributes
won't change.

Consequently concurrent kernfs_refresh_inode() calls always copy the
same values from the kernfs node.

So there's no need to take the inode i_lock to get consistent values
for generic_fillattr() and generic_permission(), the kernfs read lock
is sufficient.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Ian Kent <raven@themaw.net>
Link: https://lore.kernel.org/r/166606036215.13363.1288735296954908554.stgit@donald.themaw.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Kent 2022-10-18 10:32:42 +08:00 committed by Greg Kroah-Hartman
parent 5033ac5c58
commit aa1d058d48
1 changed files with 0 additions and 4 deletions
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4
fs/kernfs/inode.c
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@ -190,10 +190,8 @@ int kernfs_iop_getattr(struct user_namespace *mnt_userns,
struct kernfs_root *root = kernfs_root(kn); struct kernfs_root *root = kernfs_root(kn);
down_read(&root->kernfs_rwsem); down_read(&root->kernfs_rwsem);
spin_lock(&inode->i_lock);
kernfs_refresh_inode(kn, inode); kernfs_refresh_inode(kn, inode);
generic_fillattr(&init_user_ns, inode, stat); generic_fillattr(&init_user_ns, inode, stat);
spin_unlock(&inode->i_lock);
up_read(&root->kernfs_rwsem); up_read(&root->kernfs_rwsem);
return 0; return 0;
@ -288,10 +286,8 @@ int kernfs_iop_permission(struct user_namespace *mnt_userns,
root = kernfs_root(kn); root = kernfs_root(kn);
down_read(&root->kernfs_rwsem); down_read(&root->kernfs_rwsem);
spin_lock(&inode->i_lock);
kernfs_refresh_inode(kn, inode); kernfs_refresh_inode(kn, inode);
ret = generic_permission(&init_user_ns, inode, mask); ret = generic_permission(&init_user_ns, inode, mask);
spin_unlock(&inode->i_lock);
up_read(&root->kernfs_rwsem); up_read(&root->kernfs_rwsem);
return ret; return ret;