[PATCH v7 12/19] gfs2: Eliminate ip->i_gh

[Andreas Gruenbacher <agruenba@xxxxxxxxxx>]

Now that gfs2_file_buffered_write is the only remaining user of
ip->i_gh, we can move the glock holder to the stack (or rather, use the
one we already have on the stack); there is no need for keeping the
holder in the inode anymore.

This is slightly complicated by the fact that we're using ip->i_gh for
the statfs inode in gfs2_file_buffered_write as well.  Writing to the
statfs inode isn't very common, so allocate the statfs holder
dynamically when needed.

Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
---
 fs/gfs2/file.c   | 40 +++++++++++++++++++++++++++-------------
 fs/gfs2/incore.h |  3 +--
 2 files changed, 28 insertions(+), 15 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 813154d60834..5f328bc21d0b 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -876,16 +876,31 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	return written ? written : ret;
 }
 
-static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct iov_iter *from)
+static ssize_t gfs2_file_buffered_write(struct kiocb *iocb,
+					struct iov_iter *from,
+					struct gfs2_holder *gh)
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file_inode(file);
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_sbd *sdp = GFS2_SB(inode);
+	struct gfs2_holder *statfs_gh = NULL;
 	ssize_t ret;
 
-	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &ip->i_gh);
-	ret = gfs2_glock_nq(&ip->i_gh);
+	/*
+	 * In this function, we disable page faults when we're holding the
+	 * inode glock while doing I/O.  If a page fault occurs, we drop the
+	 * inode glock, fault in the pages manually, and retry.
+	 */
+
+	if (inode == sdp->sd_rindex) {
+		statfs_gh = kmalloc(sizeof(*statfs_gh), GFP_NOFS);
+		if (!statfs_gh)
+			return -ENOMEM;
+	}
+
+	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, gh);
+	ret = gfs2_glock_nq(gh);
 	if (ret)
 		goto out_uninit;
 
@@ -893,7 +908,7 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct iov_iter *fro
 		struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
 
 		ret = gfs2_glock_nq_init(m_ip->i_gl, LM_ST_EXCLUSIVE,
-					 GL_NOCACHE, &m_ip->i_gh);
+					 GL_NOCACHE, statfs_gh);
 		if (ret)
 			goto out_unlock;
 	}
@@ -902,16 +917,15 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct iov_iter *fro
 	ret = iomap_file_buffered_write(iocb, from, &gfs2_iomap_ops);
 	current->backing_dev_info = NULL;
 
-	if (inode == sdp->sd_rindex) {
-		struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
-
-		gfs2_glock_dq_uninit(&m_ip->i_gh);
-	}
+	if (inode == sdp->sd_rindex)
+		gfs2_glock_dq_uninit(statfs_gh);
 
 out_unlock:
-	gfs2_glock_dq(&ip->i_gh);
+	gfs2_glock_dq(gh);
 out_uninit:
-	gfs2_holder_uninit(&ip->i_gh);
+	gfs2_holder_uninit(gh);
+	if (statfs_gh)
+		kfree(statfs_gh);
 	return ret;
 }
 
@@ -966,7 +980,7 @@ static ssize_t gfs2_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			goto out_unlock;
 
 		iocb->ki_flags |= IOCB_DSYNC;
-		buffered = gfs2_file_buffered_write(iocb, from);
+		buffered = gfs2_file_buffered_write(iocb, from, &gh);
 		if (unlikely(buffered <= 0)) {
 			if (!ret)
 				ret = buffered;
@@ -988,7 +1002,7 @@ static ssize_t gfs2_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		if (!ret || ret2 > 0)
 			ret += ret2;
 	} else {
-		ret = gfs2_file_buffered_write(iocb, from);
+		ret = gfs2_file_buffered_write(iocb, from, &gh);
 		if (likely(ret > 0)) {
 			iocb->ki_pos += ret;
 			ret = generic_write_sync(iocb, ret);
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index e73a81db0714..87abdcc1de0c 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -387,9 +387,8 @@ struct gfs2_inode {
 	u64 i_generation;
 	u64 i_eattr;
 	unsigned long i_flags;		/* GIF_... */
-	struct gfs2_glock *i_gl; /* Move into i_gh? */
+	struct gfs2_glock *i_gl;
 	struct gfs2_holder i_iopen_gh;
-	struct gfs2_holder i_gh; /* for prepare/commit_write only */
 	struct gfs2_qadata *i_qadata; /* quota allocation data */
 	struct gfs2_holder i_rgd_gh;
 	struct gfs2_blkreserv i_res; /* rgrp multi-block reservation */
-- 
2.26.3