diff options
| author | Christian Brauner <brauner@kernel.org> | 2023-08-18 16:00:50 +0200 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2023-08-21 18:08:03 +0200 |
| commit | 5e87491415217d6bec0bcae08a3156622be2b177 (patch) | |
| tree | 1bc08f12dc38ef9397e3275c1be96382e8de87da /include/linux/fs.h | |
| parent | d8ce82efdece373b570f35acc8a29487b2087b84 (diff) | |
| download | linux-5e87491415217d6bec0bcae08a3156622be2b177.tar.gz | |
super: wait for nascent superblocks
Recent patches experiment with making it possible to allocate a new
superblock before opening the relevant block device. Naturally this has
intricate side-effects that we get to learn about while developing this.
Superblock allocators such as sget{_fc}() return with s_umount of the
new superblock held and lock ordering currently requires that block
level locks such as bdev_lock and open_mutex rank above s_umount.
Before aca740cecbe5 ("fs: open block device after superblock creation")
ordering was guaranteed to be correct as block devices were opened prior
to superblock allocation and thus s_umount wasn't held. But now s_umount
must be dropped before opening block devices to avoid locking
violations.
This has consequences. The main one being that iterators over
@super_blocks and @fs_supers that grab a temporary reference to the
superblock can now also grab s_umount before the caller has managed to
open block devices and called fill_super(). So whereas before such
iterators or concurrent mounts would have simply slept on s_umount until
SB_BORN was set or the superblock was discard due to initalization
failure they can now needlessly spin through sget{_fc}().
If the caller is sleeping on bdev_lock or open_mutex one caller waiting
on SB_BORN will always spin somewhere and potentially this can go on for
quite a while.
It should be possible to drop s_umount while allowing iterators to wait
on a nascent superblock to either be born or discarded. This patch
implements a wait_var_event() mechanism allowing iterators to sleep
until they are woken when the superblock is born or discarded.
This also allows us to avoid relooping through @fs_supers and
@super_blocks if a superblock isn't yet born or dying.
Link: aca740cecbe5 ("fs: open block device after superblock creation")
Reviewed-by: Jan Kara <jack@suse.cz>
Message-Id: <20230818-vfs-super-fixes-v3-v3-3-9f0b1876e46b@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'include/linux/fs.h')
| -rw-r--r-- | include/linux/fs.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h index 14b5777a24a0b2..17367264515622 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1095,6 +1095,7 @@ extern int send_sigurg(struct fown_struct *fown); #define SB_LAZYTIME BIT(25) /* Update the on-disk [acm]times lazily */ /* These sb flags are internal to the kernel */ +#define SB_DYING BIT(24) #define SB_SUBMOUNT BIT(26) #define SB_FORCE BIT(27) #define SB_NOSEC BIT(28) |