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kernfs: Use a per-fs rwsem to protect per-fs list of kernfs_super_info. 

Right now per-fs kernfs_rwsem protects list of kernfs_super_info instances
for a kernfs_root. Since kernfs_rwsem is used to synchronize several other
operations across kernfs and since most of these operations don't impact
kernfs_super_info, we can use a separate per-fs rwsem to synchronize access
to list of kernfs_super_info.
This helps in reducing contention around kernfs_rwsem and also allows
operations that change/access list of kernfs_super_info to proceed without
contending for kernfs_rwsem.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Link: https://lore.kernel.org/r/20230309110932.2889010-3-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Imran Khan 2023-03-09 22:09:31 +11:00 committed by Greg Kroah-Hartman
parent 9caf696142
commit c9f2dfb7b5
4 changed files with 8 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/kernfs/dir.c
View File

@ -944,6 +944,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
idr_init(&root->ino_idr);
init_rwsem(&root->kernfs_rwsem);
init_rwsem(&root->kernfs_iattr_rwsem);
init_rwsem(&root->kernfs_supers_rwsem);
INIT_LIST_HEAD(&root->supers);
/*

4
fs/kernfs/file.c
View File

@ -922,8 +922,8 @@ repeat:
root = kernfs_root(kn);
/* kick fsnotify */
down_write(&root->kernfs_rwsem);
down_read(&root->kernfs_supers_rwsem);
list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
struct kernfs_node *parent;
struct inode *p_inode = NULL;
@ -960,7 +960,7 @@ repeat:
iput(inode);
}
up_write(&root->kernfs_rwsem);
up_read(&root->kernfs_supers_rwsem);
kernfs_put(kn);
goto repeat;
}

1
fs/kernfs/kernfs-internal.h
View File

@ -48,6 +48,7 @@ struct kernfs_root {
wait_queue_head_t deactivate_waitq;
struct rw_semaphore kernfs_rwsem;
struct rw_semaphore kernfs_iattr_rwsem;
struct rw_semaphore kernfs_supers_rwsem;
};
/* +1 to avoid triggering overflow warning when negating it */

8
fs/kernfs/mount.c
View File

@ -351,9 +351,9 @@ int kernfs_get_tree(struct fs_context *fc)
}
sb->s_flags |= SB_ACTIVE;
down_write(&root->kernfs_rwsem);
down_write(&root->kernfs_supers_rwsem);
list_add(&info->node, &info->root->supers);
up_write(&root->kernfs_rwsem);
up_write(&root->kernfs_supers_rwsem);
}
fc->root = dget(sb->s_root);
@ -380,9 +380,9 @@ void kernfs_kill_sb(struct super_block *sb)
struct kernfs_super_info *info = kernfs_info(sb);
struct kernfs_root *root = info->root;
down_write(&root->kernfs_rwsem);
down_write(&root->kernfs_supers_rwsem);
list_del(&info->node);
up_write(&root->kernfs_rwsem);
up_write(&root->kernfs_supers_rwsem);
/*
* Remove the superblock from fs_supers/s_instances