On Sat, Dec 25, 2021 at 1:32 AM David Howells <dhowells@xxxxxxxxxx> wrote: > > Use an inode flag, S_KERNEL_FILE, to mark that a backing file is in use by > the kernel to prevent cachefiles or other kernel services from interfering > with that file. > > Alter rmdir to reject attempts to remove a directory marked with this flag. > This is used by cachefiles to prevent cachefilesd from removing them. > > Using S_SWAPFILE instead isn't really viable as that has other effects in > the I/O paths. > > Changes > ======= > ver #3: > - Check for the object pointer being NULL in the tracepoints rather than > the caller. > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> > cc: linux-cachefs@xxxxxxxxxx > Link: https://lore.kernel.org/r/163819630256.215744.4815885535039369574.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1 > Link: https://lore.kernel.org/r/163906931596.143852.8642051223094013028.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2 > Link: https://lore.kernel.org/r/163967141000.1823006.12920680657559677789.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3 > --- > > fs/cachefiles/Makefile | 1 + > fs/cachefiles/namei.c | 43 +++++++++++++++++++++++++++++++++++++ > fs/namei.c | 3 ++- > include/linux/fs.h | 1 + > include/trace/events/cachefiles.h | 42 ++++++++++++++++++++++++++++++++++++ > 5 files changed, 89 insertions(+), 1 deletion(-) > create mode 100644 fs/cachefiles/namei.c > > diff --git a/fs/cachefiles/Makefile b/fs/cachefiles/Makefile > index 463e3d608b75..e0b092ca077f 100644 > --- a/fs/cachefiles/Makefile > +++ b/fs/cachefiles/Makefile > @@ -7,6 +7,7 @@ cachefiles-y := \ > cache.o \ > daemon.o \ > main.o \ > + namei.o \ > security.o > > cachefiles-$(CONFIG_CACHEFILES_ERROR_INJECTION) += error_inject.o > diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c > new file mode 100644 > index 000000000000..913f83f1c900 > --- /dev/null > +++ b/fs/cachefiles/namei.c > @@ -0,0 +1,43 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +/* CacheFiles path walking and related routines > + * > + * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved. > + * Written by David Howells (dhowells@xxxxxxxxxx) > + */ > + > +#include <linux/fs.h> > +#include "internal.h" > + > +/* > + * Mark the backing file as being a cache file if it's not already in use. The > + * mark tells the culling request command that it's not allowed to cull the > + * file or directory. The caller must hold the inode lock. > + */ > +static bool __cachefiles_mark_inode_in_use(struct cachefiles_object *object, > + struct dentry *dentry) > +{ > + struct inode *inode = d_backing_inode(dentry); > + bool can_use = false; > + > + if (!(inode->i_flags & S_KERNEL_FILE)) { > + inode->i_flags |= S_KERNEL_FILE; > + trace_cachefiles_mark_active(object, inode); > + can_use = true; > + } else { > + pr_notice("cachefiles: Inode already in use: %pd\n", dentry); > + } > + > + return can_use; > +} > + > +/* > + * Unmark a backing inode. The caller must hold the inode lock. > + */ > +static void __cachefiles_unmark_inode_in_use(struct cachefiles_object *object, > + struct dentry *dentry) > +{ > + struct inode *inode = d_backing_inode(dentry); > + > + inode->i_flags &= ~S_KERNEL_FILE; > + trace_cachefiles_mark_inactive(object, inode); > +} > diff --git a/fs/namei.c b/fs/namei.c > index 1f9d2187c765..d81f04f8d818 100644 > --- a/fs/namei.c > +++ b/fs/namei.c > @@ -3958,7 +3958,8 @@ int vfs_rmdir(struct user_namespace *mnt_userns, struct inode *dir, > inode_lock(dentry->d_inode); > > error = -EBUSY; > - if (is_local_mountpoint(dentry)) > + if (is_local_mountpoint(dentry) || > + (dentry->d_inode->i_flags & S_KERNEL_FILE)) Better as this check to the many other checks in may_delete() > goto out; > > error = security_inode_rmdir(dir, dentry); > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 2c0b8e77d9ab..bcf1ca430139 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -2249,6 +2249,7 @@ struct super_operations { > #define S_ENCRYPTED (1 << 14) /* Encrypted file (using fs/crypto/) */ > #define S_CASEFOLD (1 << 15) /* Casefolded file */ > #define S_VERITY (1 << 16) /* Verity file (using fs/verity/) */ > +#define S_KERNEL_FILE (1 << 17) /* File is in use by the kernel (eg. fs/cachefiles) */ > Trying to brand this flag as a generic "in use by kernel" is misleading. Modules other than cachefiles cannot set/clear this flag, because then cachefiles won't know that it is allowed to set/clear the flag. So I think it would be better to call it for what it really is - an inode flag that is controlled by cachefiles. Also, the name KERNEL_FILE for a directory is a bit confusing IMO. Perhaps S_CACHEFILES? Thanks, Amir.
