bcachefs grabs s_umount and sets SB_RDONLY when the fs is shutdown via the ioctl() interface. This has a couple issues related to interactions between shutdown and freeze:
1. The flags == FSOP_GOING_FLAGS_DEFAULT case is a deadlock vector because freeze_bdev() calls into freeze_super(), which also acquires s_umount. 2. If an explicit shutdown occurs while the sb is frozen, SB_RDONLY alters the thaw path as if the sb was read-only at freeze time. This effectively leaks the frozen state and leaves the sb frozen indefinitely. The usage of SB_RDONLY here goes back to the initial bcachefs commit and AFAICT is simply historical behavior. This behavior is unique to bcachefs relative to the handful of other filesystems that support the shutdown ioctl(). Typically, SB_RDONLY is reserved for the proper remount path, which itself is restricted from modifying frozen superblocks in reconfigure_super(). Drop the unnecessary sb lock and flags update bch2_ioc_goingdown() to address both of these issues. Signed-off-by: Brian Foster <[email protected]> --- This is currently churning through CI here (though I had already pushed an early version that ran clean): https://evilpiepirate.org/~testdashboard/ci?branch=bfoster Brian fs/bcachefs/fs-ioctl.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) diff --git a/fs/bcachefs/fs-ioctl.c b/fs/bcachefs/fs-ioctl.c index 5a39bcb597a3..0baa23c35ef5 100644 --- a/fs/bcachefs/fs-ioctl.c +++ b/fs/bcachefs/fs-ioctl.c @@ -287,34 +287,26 @@ static int bch2_ioc_goingdown(struct bch_fs *c, u32 __user *arg) bch_notice(c, "shutdown by ioctl type %u", flags); - down_write(&c->vfs_sb->s_umount); - switch (flags) { case FSOP_GOING_FLAGS_DEFAULT: ret = freeze_bdev(c->vfs_sb->s_bdev); if (ret) - goto err; - + break; bch2_journal_flush(&c->journal); - c->vfs_sb->s_flags |= SB_RDONLY; bch2_fs_emergency_read_only(c); thaw_bdev(c->vfs_sb->s_bdev); break; - case FSOP_GOING_FLAGS_LOGFLUSH: bch2_journal_flush(&c->journal); fallthrough; - case FSOP_GOING_FLAGS_NOLOGFLUSH: - c->vfs_sb->s_flags |= SB_RDONLY; bch2_fs_emergency_read_only(c); break; default: ret = -EINVAL; break; } -err: - up_write(&c->vfs_sb->s_umount); + return ret; } -- 2.41.0
