gfs2: Stop using glock holder auto-demotion for now

We're having unresolved issues with the glock holder auto-demotion mechanism
introduced in commit dc73290.  This mechanism was assumed to be essential
for avoiding frequent short reads and writes until commit 296abc0
("gfs2: No short reads or writes upon glock contention").  Since then,
when the inode glock is lost, it is simply re-acquired and the operation
is resumed.  This means that apart from the performance penalty, we
might as well drop the inode glock before faulting in pages, and
re-acquire it afterwards.

Signed-off-by: Andreas Gruenbacher <[email protected]>

fs/gfs2/file.c

@@ -832,7 +832,6 @@ static ssize_t gfs2_file_direct_read(struct kiocb *iocb, struct iov_iter *to,
  ret = gfs2_glock_nq(gh);
  if (ret)
  goto out_uninit;
-retry_under_glock:
  pagefault_disable();
  to->nofault = true;
  ret = iomap_dio_rw(iocb, to, &gfs2_iomap_ops, NULL,
@@ -845,14 +844,10 @@ static ssize_t gfs2_file_direct_read(struct kiocb *iocb, struct iov_iter *to,
  read = ret;
 
  if (should_fault_in_pages(to, iocb, &prev_count, &window_size)) {
- gfs2_holder_allow_demote(gh);
+ gfs2_glock_dq(gh);
  window_size -= fault_in_iov_iter_writeable(to, window_size);
- gfs2_holder_disallow_demote(gh);
- if (window_size) {
- if (gfs2_holder_queued(gh))
- goto retry_under_glock;
+ if (window_size)
  goto retry;
- }
  }
 out_unlock:
  if (gfs2_holder_queued(gh))
@@ -900,7 +895,6 @@ static ssize_t gfs2_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
  /* Silently fall back to buffered I/O when writing beyond EOF */
  if (iocb->ki_pos + iov_iter_count(from) > i_size_read(&ip->i_inode))
  goto out_unlock;
-retry_under_glock:
 
  from->nofault = true;
  ret = iomap_dio_rw(iocb, from, &gfs2_iomap_ops, NULL,
@@ -916,14 +910,10 @@ static ssize_t gfs2_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
  written = ret;
 
  if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
- gfs2_holder_allow_demote(gh);
+ gfs2_glock_dq(gh);
  window_size -= fault_in_iov_iter_readable(from, window_size);
- gfs2_holder_disallow_demote(gh);
- if (window_size) {
- if (gfs2_holder_queued(gh))
- goto retry_under_glock;
+ if (window_size)
  goto retry;
- }
  }
 out_unlock:
  if (gfs2_holder_queued(gh))
@@ -974,7 +964,6 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
  ret = gfs2_glock_nq(&gh);
  if (ret)
  goto out_uninit;
-retry_under_glock:
  pagefault_disable();
  ret = generic_file_read_iter(iocb, to);
  pagefault_enable();
@@ -984,14 +973,10 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
  read += ret;
 
  if (should_fault_in_pages(to, iocb, &prev_count, &window_size)) {
- gfs2_holder_allow_demote(&gh);
+ gfs2_glock_dq(&gh);
  window_size -= fault_in_iov_iter_writeable(to, window_size);
- gfs2_holder_disallow_demote(&gh);
- if (window_size) {
- if (gfs2_holder_queued(&gh))
- goto retry_under_glock;
+ if (window_size)
  goto retry;
- }
  }
 out_unlock:
  if (gfs2_holder_queued(&gh))
@@ -1030,22 +1015,17 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb,
 
  gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, gh);
 retry:
- ret = gfs2_glock_nq(gh);
- if (ret)
- goto out_uninit;
  if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
-retry_under_glock:
- gfs2_holder_allow_demote(gh);
  window_size -= fault_in_iov_iter_readable(from, window_size);
- gfs2_holder_disallow_demote(gh);
  if (!window_size) {
  ret = -EFAULT;
- goto out_unlock;
+ goto out_uninit;
  }
- if (!gfs2_holder_queued(gh))
- goto retry;
  from->count = min(from->count, window_size);
  }
+ ret = gfs2_glock_nq(gh);
+ if (ret)
+ goto out_uninit;
 
  if (inode == sdp->sd_rindex) {
  struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
@@ -1073,8 +1053,10 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb,
  goto out_unlock;
 
  from->count = orig_count - written;
- if (should_fault_in_pages(from, iocb, &prev_count, &window_size))
- goto retry_under_glock;
+ if (should_fault_in_pages(from, iocb, &prev_count, &window_size)) {
+ gfs2_glock_dq(gh);
+ goto retry;
+ }
 out_unlock:
  if (gfs2_holder_queued(gh))
  gfs2_glock_dq(gh);