Re: [RFC PATCH 08/12] nfs: convert lock handling to use file_lock_context

J. Bruce Fields
2014-09-10T19:17:37Z

On Wed, Sep 10, 2014 at 10:28:46AM -0400, Jeff Layton wrote:
> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
> ---
> fs/nfs/delegation.c | 37 +++++++++++++++++++++----------------
> fs/nfs/nfs4state.c | 24 +++++++++++++++---------
> fs/nfs/pagelist.c | 3 ++-
> fs/nfs/write.c | 39 +++++++++++++++++++++++++++++++++------
> 4 files changed, 71 insertions(+), 32 deletions(-)
>
> diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
> index 5853f53db732..22c6eed9bb5b 100644
> --- a/fs/nfs/delegation.c
> +++ b/fs/nfs/delegation.c
> @@ -85,25 +85,30 @@ static int nfs_delegation_claim_locks(struct nfs_open_context *ctx, struct nfs4_
> {
> struct inode *inode = state->inode;
> struct file_lock *fl;
> + struct file_lock_context *flctx = inode->i_flctx;
> + struct list_head *list;
> int status = 0;
>
> - if (inode->i_flock == NULL)
> - goto out;
> -
> - /* Protect inode->i_flock using the i_lock */
> - spin_lock(&inode->i_lock);
> - for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
> - if (!(fl->fl_flags & (FL_POSIX|FL_FLOCK)))
> - continue;
> - if (nfs_file_open_context(fl->fl_file) != ctx)
> - continue;
> - spin_unlock(&inode->i_lock);
> - status = nfs4_lock_delegation_recall(fl, state, stateid);
> - if (status < 0)
> - goto out;
> - spin_lock(&inode->i_lock);
> + flctx = inode->i_flctx;
> + if (flctx) {
> + list = &flctx->flc_posix;
> + spin_lock(&flctx->flc_lock);
> +restart:
> + list_for_each_entry(fl, list, fl_list) {
> + if (nfs_file_open_context(fl->fl_file) != ctx)
> + continue;
> + spin_unlock(&flctx->flc_lock);
> + status = nfs4_lock_delegation_recall(fl, state, stateid);
> + if (status < 0)
> + goto out;
> + spin_lock(&flctx->flc_lock);
> + }
> + if (list == &flctx->flc_posix) {
> + list = &flctx->flc_flock;
> + goto restart;
> + }
> + spin_unlock(&flctx->flc_lock);
> }
> - spin_unlock(&inode->i_lock);
> out:
> return status;
> }
> diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
> index a043f618cd5a..2899a0f26293 100644
> --- a/fs/nfs/nfs4state.c
> +++ b/fs/nfs/nfs4state.c
> @@ -1377,21 +1377,23 @@ static int nfs4_reclaim_locks(struct nfs4_state *state, const struct nfs4_state_
> struct inode *inode = state->inode;
> struct nfs_inode *nfsi = NFS_I(inode);
> struct file_lock *fl;
> + struct file_lock_context *flctx = inode->i_flctx;
> + struct list_head *list;
> int status = 0;
>
> - if (inode->i_flock == NULL)
> + if (!flctx)
> return 0;
>
> + list = &flctx->flc_posix;
> +
> /* Guard against delegation returns and new lock/unlock calls */
> down_write(&nfsi->rwsem);
> - /* Protect inode->i_flock using the BKL */
> - spin_lock(&inode->i_lock);
> - for (fl = inode->i_flock; fl != NULL; fl = fl->fl_next) {
> - if (!(fl->fl_flags & (FL_POSIX|FL_FLOCK)))
> - continue;
> + spin_lock(&flctx->flc_lock);
> +restart:
> + list_for_each_entry(fl, list, fl_list) {
> if (nfs_file_open_context(fl->fl_file)->state != state)
> continue;
> - spin_unlock(&inode->i_lock);
> + spin_unlock(&flctx->flc_lock);
> status = ops->recover_lock(state, fl);
> switch (status) {
> case 0:
> @@ -1418,9 +1420,13 @@ static int nfs4_reclaim_locks(struct nfs4_state *state, const struct nfs4_state_
> /* kill_proc(fl->fl_pid, SIGLOST, 1); */
> status = 0;
> }
> - spin_lock(&inode->i_lock);
> + spin_lock(&flctx->flc_lock);
> }
> - spin_unlock(&inode->i_lock);
> + if (list == &flctx->flc_posix) {
> + list = &flctx->flc_flock;
> + goto restart;
> + }
> + spin_unlock(&flctx->flc_lock);
> out:
> up_write(&nfsi->rwsem);
> return status;
> diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
> index ba491926df5f..4df8d8755026 100644
> --- a/fs/nfs/pagelist.c
> +++ b/fs/nfs/pagelist.c
> @@ -782,7 +782,8 @@ static bool nfs_can_coalesce_requests(struct nfs_page *prev,
> if (prev) {
> if (!nfs_match_open_context(req->wb_context, prev->wb_context))
> return false;
> - if (req->wb_context->dentry->d_inode->i_flock != NULL &&
> + if (req->wb_context->dentry->d_inode->i_flctx != NULL &&
> + !list_empty(&req->wb_context->dentry->d_inode->i_flctx->flc_posix) &&
> !nfs_match_lock_context(req->wb_lock_context,
> prev->wb_lock_context))
> return false;
> diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> index e3b5cf28bdc5..02b8777f8f2f 100644
> --- a/fs/nfs/write.c
> +++ b/fs/nfs/write.c
> @@ -1128,7 +1128,8 @@ int nfs_flush_incompatible(struct file *file, struct page *page)
> do_flush = req->wb_page != page || req->wb_context != ctx;
> /* for now, flush if more than 1 request in page_group */
> do_flush |= req->wb_this_page != req;
> - if (l_ctx && ctx->dentry->d_inode->i_flock != NULL) {
> + if (l_ctx && ctx->dentry->d_inode->i_flctx &&
> + !list_empty(&ctx->dentry->d_inode->i_flctx->flc_posix)) {
> do_flush |= l_ctx->lockowner.l_owner != current->files
> || l_ctx->lockowner.l_pid != current->tgid;
> }
> @@ -1189,6 +1190,12 @@ out:
> return PageUptodate(page) != 0;
> }
>
> +static bool
> +is_whole_file_wrlock(struct file_lock *fl)
> +{
> + return fl->fl_start == 0 && fl->fl_end == OFFSET_MAX && fl->fl_type == F_WRLCK;
> +}
> +
> /* If we know the page is up to date, and we're not using byte range locks (or
> * if we have the whole file locked for writing), it may be more efficient to
> * extend the write to cover the entire page in order to avoid fragmentation
> @@ -1199,17 +1206,37 @@ out:
> */
> static int nfs_can_extend_write(struct file *file, struct page *page, struct inode *inode)
> {
> + int ret;
> + struct file_lock_context *flctx = inode->i_flctx;
> + struct file_lock *fl;
> +
> if (file->f_flags & O_DSYNC)
> return 0;
> if (!nfs_write_pageuptodate(page, inode))
> return 0;
> if (NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
> return 1;
> - if (inode->i_flock == NULL || (inode->i_flock->fl_start == 0 &&
> - inode->i_flock->fl_end == OFFSET_MAX &&
> - inode->i_flock->fl_type != F_RDLCK))

Doesn't the existing code already have a bug? Without the i_lock
inode->i_flock could turn NULL partyway through

There's a bug in the existing code, isn't there? Without holding the
i_lock, couldn't inode->i_flock turn NULL partway through this
conditional and cause NULL dereferences? (Or, more bizarrely, the
checks of those various fields could end up being for different locks.)

> - return 1;
> - return 0;
> + /* no lock context == no locks */
> + if (!flctx)
> + return 0;
> +
> + /* if lists are empty then there are no locks */
> + if (list_empty(&flctx->flc_posix) && list_empty(&flctx->flc_flock))
> + return 0;
> +
> + ret = 0;
> + /* Check to see if there are whole file write locks */
> + spin_lock(&flctx->flc_lock);
> + fl = list_first_entry(&flctx->flc_posix, struct file_lock, fl_list);
> + if (is_whole_file_wrlock(fl)) {
> + ret = 1;
> + } else {
> + fl = list_first_entry(&flctx->flc_flock, struct file_lock, fl_list);
> + if (is_whole_file_wrlock(fl))
> + ret = 1;
> + }
> + spin_unlock(&flctx->flc_lock);
> + return ret;

Kind of pity we're turning 5 lines of code into 20 in the name of
simplification. Could be slightly pithier:

ret = is_whole_file_wrlock(fl);
if (!ret) {
fl = ...
ret = is_whole_file_wrlock(fl);
}

But, whatever, looks OK to me.

--b.

> }
>
> /*
> --
> 1.9.3
>