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gfs2: Fix iomap write page reclaim deadlock
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Since commit 64bc06b ("gfs2: iomap buffered write support"), gfs2 is doing
buffered writes by starting a transaction in iomap_begin, writing a range of
pages, and ending that transaction in iomap_end.  This approach suffers from
two problems:

  (1) Any allocations necessary for the write are done in iomap_begin, so when
  the data aren't journaled, there is no need for keeping the transaction open
  until iomap_end.

  (2) Transactions keep the gfs2 log flush lock held.  When
  iomap_file_buffered_write calls balance_dirty_pages, this can end up calling
  gfs2_write_inode, which will try to flush the log.  This requires taking the
  log flush lock which is already held, resulting in a deadlock.

Fix both of these issues by not keeping transactions open from iomap_begin to
iomap_end.  Instead, start a small transaction in page_prepare and end it in
page_done when necessary.

Reported-by: Edwin Török <[email protected]>
Fixes: 64bc06b ("gfs2: iomap buffered write support")
Signed-off-by: Andreas Gruenbacher <[email protected]>
Signed-off-by: Bob Peterson <[email protected]>
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Andreas Gruenbacher committed May 7, 2019
1 parent 8f91821 commit d0a22a4
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Showing 2 changed files with 58 additions and 44 deletions.
14 changes: 10 additions & 4 deletions fs/gfs2/aops.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -649,18 +649,21 @@ static int gfs2_readpages(struct file *file, struct address_space *mapping,
*/
void adjust_fs_space(struct inode *inode)
{
struct gfs2_sbd *sdp = inode->i_sb->s_fs_info;
struct gfs2_sbd *sdp = GFS2_SB(inode);
struct gfs2_inode *m_ip = GFS2_I(sdp->sd_statfs_inode);
struct gfs2_inode *l_ip = GFS2_I(sdp->sd_sc_inode);
struct gfs2_statfs_change_host *m_sc = &sdp->sd_statfs_master;
struct gfs2_statfs_change_host *l_sc = &sdp->sd_statfs_local;
struct buffer_head *m_bh, *l_bh;
u64 fs_total, new_free;

if (gfs2_trans_begin(sdp, 2 * RES_STATFS, 0) != 0)
return;

/* Total up the file system space, according to the latest rindex. */
fs_total = gfs2_ri_total(sdp);
if (gfs2_meta_inode_buffer(m_ip, &m_bh) != 0)
return;
goto out;

spin_lock(&sdp->sd_statfs_spin);
gfs2_statfs_change_in(m_sc, m_bh->b_data +
Expand All @@ -675,11 +678,14 @@ void adjust_fs_space(struct inode *inode)
gfs2_statfs_change(sdp, new_free, new_free, 0);

if (gfs2_meta_inode_buffer(l_ip, &l_bh) != 0)
goto out;
goto out2;
update_statfs(sdp, m_bh, l_bh);
brelse(l_bh);
out:
out2:
brelse(m_bh);
out:
sdp->sd_rindex_uptodate = 0;
gfs2_trans_end(sdp);
}

/**
Expand Down
88 changes: 48 additions & 40 deletions fs/gfs2/bmap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -991,17 +991,28 @@ static void gfs2_write_unlock(struct inode *inode)
gfs2_glock_dq_uninit(&ip->i_gh);
}

static int gfs2_iomap_page_prepare(struct inode *inode, loff_t pos,
unsigned len, struct iomap *iomap)
{
struct gfs2_sbd *sdp = GFS2_SB(inode);

return gfs2_trans_begin(sdp, RES_DINODE + (len >> inode->i_blkbits), 0);
}

static void gfs2_iomap_page_done(struct inode *inode, loff_t pos,
unsigned copied, struct page *page,
struct iomap *iomap)
{
struct gfs2_inode *ip = GFS2_I(inode);
struct gfs2_sbd *sdp = GFS2_SB(inode);

if (page)
if (page && !gfs2_is_stuffed(ip))
gfs2_page_add_databufs(ip, page, offset_in_page(pos), copied);
gfs2_trans_end(sdp);
}

static const struct iomap_page_ops gfs2_iomap_page_ops = {
.page_prepare = gfs2_iomap_page_prepare,
.page_done = gfs2_iomap_page_done,
};

Expand Down Expand Up @@ -1057,31 +1068,45 @@ static int gfs2_iomap_begin_write(struct inode *inode, loff_t pos,
if (alloc_required)
rblocks += gfs2_rg_blocks(ip, data_blocks + ind_blocks);

ret = gfs2_trans_begin(sdp, rblocks, iomap->length >> inode->i_blkbits);
if (ret)
goto out_trans_fail;
if (unstuff || iomap->type == IOMAP_HOLE) {
struct gfs2_trans *tr;

if (unstuff) {
ret = gfs2_unstuff_dinode(ip, NULL);
ret = gfs2_trans_begin(sdp, rblocks,
iomap->length >> inode->i_blkbits);
if (ret)
goto out_trans_end;
release_metapath(mp);
ret = gfs2_iomap_get(inode, iomap->offset, iomap->length,
flags, iomap, mp);
if (ret)
goto out_trans_end;
}
goto out_trans_fail;

if (iomap->type == IOMAP_HOLE) {
ret = gfs2_iomap_alloc(inode, iomap, flags, mp);
if (ret) {
gfs2_trans_end(sdp);
gfs2_inplace_release(ip);
punch_hole(ip, iomap->offset, iomap->length);
goto out_qunlock;
if (unstuff) {
ret = gfs2_unstuff_dinode(ip, NULL);
if (ret)
goto out_trans_end;
release_metapath(mp);
ret = gfs2_iomap_get(inode, iomap->offset,
iomap->length, flags, iomap, mp);
if (ret)
goto out_trans_end;
}

if (iomap->type == IOMAP_HOLE) {
ret = gfs2_iomap_alloc(inode, iomap, flags, mp);
if (ret) {
gfs2_trans_end(sdp);
gfs2_inplace_release(ip);
punch_hole(ip, iomap->offset, iomap->length);
goto out_qunlock;
}
}

tr = current->journal_info;
if (tr->tr_num_buf_new)
__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
else
gfs2_trans_add_meta(ip->i_gl, mp->mp_bh[0]);

gfs2_trans_end(sdp);
}
if (!gfs2_is_stuffed(ip) && gfs2_is_jdata(ip))

if (gfs2_is_stuffed(ip) || gfs2_is_jdata(ip))
iomap->page_ops = &gfs2_iomap_page_ops;
return 0;

Expand Down Expand Up @@ -1121,10 +1146,6 @@ static int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
iomap->type != IOMAP_MAPPED)
ret = -ENOTBLK;
}
if (!ret) {
get_bh(mp.mp_bh[0]);
iomap->private = mp.mp_bh[0];
}
release_metapath(&mp);
trace_gfs2_iomap_end(ip, iomap, ret);
return ret;
Expand All @@ -1135,27 +1156,16 @@ static int gfs2_iomap_end(struct inode *inode, loff_t pos, loff_t length,
{
struct gfs2_inode *ip = GFS2_I(inode);
struct gfs2_sbd *sdp = GFS2_SB(inode);
struct gfs2_trans *tr = current->journal_info;
struct buffer_head *dibh = iomap->private;

if ((flags & (IOMAP_WRITE | IOMAP_DIRECT)) != IOMAP_WRITE)
goto out;

if (iomap->type != IOMAP_INLINE) {
if (!gfs2_is_stuffed(ip))
gfs2_ordered_add_inode(ip);

if (tr->tr_num_buf_new)
__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
else
gfs2_trans_add_meta(ip->i_gl, dibh);
}

if (inode == sdp->sd_rindex) {
if (inode == sdp->sd_rindex)
adjust_fs_space(inode);
sdp->sd_rindex_uptodate = 0;
}

gfs2_trans_end(sdp);
gfs2_inplace_release(ip);

if (length != written && (iomap->flags & IOMAP_F_NEW)) {
Expand All @@ -1175,8 +1185,6 @@ static int gfs2_iomap_end(struct inode *inode, loff_t pos, loff_t length,
gfs2_write_unlock(inode);

out:
if (dibh)
brelse(dibh);
return 0;
}

Expand Down

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