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nfs: block notification on fs with its own ->lock 

NFSv4.1 supports an optional lock notification feature which notifies
the client when a lock comes available.  (Normally NFSv4 clients just
poll for locks if necessary.)  To make that work, we need to request a
blocking lock from the filesystem.

We turned that off for NFS in commit f657f8eef3 ("nfs: don't atempt
blocking locks on nfs reexports") [sic] because it actually blocks the
nfsd thread while waiting for the lock.

Thanks to Vasily Averin for pointing out that NFS isn't the only
filesystem with that problem.

Any filesystem that leaves ->lock NULL will use posix_lock_file(), which
does the right thing.  Simplest is just to assume that any filesystem
that defines its own ->lock is not safe to request a blocking lock from.

So, this patch mostly reverts commit f657f8eef3 ("nfs: don't atempt
blocking locks on nfs reexports") [sic] and commit b840be2f00 ("lockd:
don't attempt blocking locks on nfs reexports"), and instead uses a
check of ->lock (Vasily's suggestion) to decide whether to support
blocking lock notifications on a given filesystem.  Also add a little
documentation.

Perhaps someday we could add back an export flag later to allow
filesystems with "good" ->lock methods to support blocking lock
notifications.

Reported-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[ cel: Description rewritten to address checkpatch nits ]
[ cel: Fixed warning when SUNRPC debugging is disabled ]
[ cel: Fixed NULL check ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Vasily Averin <vvs@virtuozzo.com>
This commit is contained in:
J. Bruce Fields 2021-12-16 12:20:13 -05:00 committed by Chuck Lever
parent cd2e999c7c
commit 40595cdc93
5 changed files with 24 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
fs/lockd/svclock.c
View File

@ -470,8 +470,10 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
struct nlm_host *host, struct nlm_lock *lock, int wait,
struct nlm_cookie *cookie, int reclaim)
{
struct nlm_block *block = NULL;
#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
struct inode *inode = nlmsvc_file_inode(file);
#endif
struct nlm_block *block = NULL;
int error;
int mode;
int async_block = 0;
@ -484,7 +486,7 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
(long long)lock->fl.fl_end,
wait);
if (inode->i_sb->s_export_op->flags & EXPORT_OP_SYNC_LOCKS) {
if (nlmsvc_file_file(file)->f_op->lock) {
async_block = wait;
wait = 0;
}

2
fs/nfs/export.c
View File

@ -158,5 +158,5 @@ const struct export_operations nfs_export_ops = {
.fetch_iversion = nfs_fetch_iversion,
.flags = EXPORT_OP_NOWCC|EXPORT_OP_NOSUBTREECHK|
EXPORT_OP_CLOSE_BEFORE_UNLINK|EXPORT_OP_REMOTE_FS|
EXPORT_OP_NOATOMIC_ATTR|EXPORT_OP_SYNC_LOCKS,
EXPORT_OP_NOATOMIC_ATTR,
};

18
fs/nfsd/nfs4state.c
View File

@ -6842,7 +6842,6 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
struct nfsd4_blocked_lock *nbl = NULL;
struct file_lock *file_lock = NULL;
struct file_lock *conflock = NULL;
struct super_block *sb;
__be32 status = 0;
int lkflg;
int err;
@ -6864,7 +6863,6 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
dprintk("NFSD: nfsd4_lock: permission denied!\n");
return status;
}
sb = cstate->current_fh.fh_dentry->d_sb;
if (lock->lk_is_new) {
if (nfsd4_has_session(cstate))
@ -6916,8 +6914,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
fp = lock_stp->st_stid.sc_file;
switch (lock->lk_type) {
case NFS4_READW_LT:
if (nfsd4_has_session(cstate) &&
!(sb->s_export_op->flags & EXPORT_OP_SYNC_LOCKS))
if (nfsd4_has_session(cstate))
fl_flags |= FL_SLEEP;
fallthrough;
case NFS4_READ_LT:
@ -6929,8 +6926,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
fl_type = F_RDLCK;
break;
case NFS4_WRITEW_LT:
if (nfsd4_has_session(cstate) &&
!(sb->s_export_op->flags & EXPORT_OP_SYNC_LOCKS))
if (nfsd4_has_session(cstate))
fl_flags |= FL_SLEEP;
fallthrough;
case NFS4_WRITE_LT:
@ -6951,6 +6947,16 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
goto out;
}
/*
* Most filesystems with their own ->lock operations will block
* the nfsd thread waiting to acquire the lock. That leads to
* deadlocks (we don't want every nfsd thread tied up waiting
* for file locks), so don't attempt blocking lock notifications
* on those filesystems:
*/
if (nf->nf_file->f_op->lock)
fl_flags &= ~FL_SLEEP;
nbl = find_or_allocate_block(lock_sop, &fp->fi_fhandle, nn);
if (!nbl) {
dprintk("NFSD: %s: unable to allocate block!\n", __func__);

2
include/linux/exportfs.h
View File

@ -221,8 +221,6 @@ struct export_operations {
#define EXPORT_OP_NOATOMIC_ATTR (0x10) /* Filesystem cannot supply
atomic attribute updates
*/
#define EXPORT_OP_SYNC_LOCKS (0x20) /* Filesystem can't do
asychronous blocking locks */
unsigned long flags;
};

9
include/linux/lockd/lockd.h
View File

@ -303,10 +303,15 @@ void nlmsvc_invalidate_all(void);
int nlmsvc_unlock_all_by_sb(struct super_block *sb);
int nlmsvc_unlock_all_by_ip(struct sockaddr *server_addr);
static inline struct file *nlmsvc_file_file(struct nlm_file *file)
{
return file->f_file[O_RDONLY] ?
file->f_file[O_RDONLY] : file->f_file[O_WRONLY];
}
static inline struct inode *nlmsvc_file_inode(struct nlm_file *file)
{
return locks_inode(file->f_file[O_RDONLY] ?
file->f_file[O_RDONLY] : file->f_file[O_WRONLY]);
return locks_inode(nlmsvc_file_file(file));
}
static inline int __nlm_privileged_request4(const struct sockaddr *sap)