ext4: Turn off multiple page-io submission by default

Jon Nelson has found a test case which causes postgresql to fail with
the error:

psql:t.sql:4: ERROR: invalid page header in block 38269 of relation base/16384/16581

Under memory pressure, it looks like part of a file can end up getting
replaced by zero's.  Until we can figure out the cause, we'll roll
back the change and use block_write_full_page() instead of
ext4_bio_write_page().  The new, more efficient writing function can
be used via the mount option mblk_io_submit, so we can test and fix
the new page I/O code.

To reproduce the problem, install postgres 8.4 or 9.0, and pin enough
memory such that the system just at the end of triggering writeback
before running the following sql script:

begin;
create temporary table foo as select x as a, ARRAY[x] as b FROM
generate_series(1, 10000000 ) AS x;
create index foo_a_idx on foo (a);
create index foo_b_idx on foo USING GIN (b);
rollback;

If the temporary table is created on a hard drive partition which is
encrypted using dm_crypt, then under memory pressure, approximately
30-40% of the time, pgsql will issue the above failure.

This patch should fix this problem, and the problem will come back if
the file system is mounted with the mblk_io_submit mount option.

Reported-by: Jon Nelson <jnelson@jamponi.net>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 12 insertions, 2 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e32195d6aac3..fb15c9c0be74 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1026,6 +1026,8 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 	    !(def_mount_opts & EXT4_DEFM_NODELALLOC))
 		seq_puts(seq, ",nodelalloc");
 
+	if (test_opt(sb, MBLK_IO_SUBMIT))
+		seq_puts(seq, ",mblk_io_submit");
 	if (sbi->s_stripe)
 		seq_printf(seq, ",stripe=%lu", sbi->s_stripe);
 	/*
@@ -1239,8 +1241,8 @@ enum {
 	Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_jqfmt_vfsv1, Opt_quota,
 	Opt_noquota, Opt_ignore, Opt_barrier, Opt_nobarrier, Opt_err,
 	Opt_resize, Opt_usrquota, Opt_grpquota, Opt_i_version,
-	Opt_stripe, Opt_delalloc, Opt_nodelalloc,
-	Opt_block_validity, Opt_noblock_validity,
+	Opt_stripe, Opt_delalloc, Opt_nodelalloc, Opt_mblk_io_submit,
+	Opt_nomblk_io_submit, Opt_block_validity, Opt_noblock_validity,
 	Opt_inode_readahead_blks, Opt_journal_ioprio,
 	Opt_dioread_nolock, Opt_dioread_lock,
 	Opt_discard, Opt_nodiscard,
@@ -1304,6 +1306,8 @@ static const match_table_t tokens = {
 	{Opt_resize, "resize"},
 	{Opt_delalloc, "delalloc"},
 	{Opt_nodelalloc, "nodelalloc"},
+	{Opt_mblk_io_submit, "mblk_io_submit"},
+	{Opt_nomblk_io_submit, "nomblk_io_submit"},
 	{Opt_block_validity, "block_validity"},
 	{Opt_noblock_validity, "noblock_validity"},
 	{Opt_inode_readahead_blks, "inode_readahead_blks=%u"},
@@ -1725,6 +1729,12 @@ set_qf_format:
 		case Opt_nodelalloc:
 			clear_opt(sbi->s_mount_opt, DELALLOC);
 			break;
+		case Opt_mblk_io_submit:
+			set_opt(sbi->s_mount_opt, MBLK_IO_SUBMIT);
+			break;
+		case Opt_nomblk_io_submit:
+			clear_opt(sbi->s_mount_opt, MBLK_IO_SUBMIT);
+			break;
 		case Opt_stripe:
 			if (match_int(&args[0], &option))
 				return 0;