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Prakash Surya ef7a79488a OpenZFS 8997 - ztest assertion failure in zil_lwb_write_issue
PROBLEM
=======

When `dmu_tx_assign` is called from `zil_lwb_write_issue`, it's possible
for either `ERESTART` or `EIO` to be returned.

If `ERESTART` is returned, this will cause an assertion to fail directly
in `zil_lwb_write_issue`, where the code assumes the return value is
`EIO` if `dmu_tx_assign` returns a non-zero value. This can occur if the
SPA is suspended when `dmu_tx_assign` is called, and most often occurs
when running `zloop`.

If `EIO` is returned, this can cause assertions to fail elsewhere in the
ZIL code. For example, `zil_commit_waiter_timeout` contains the
following logic:

    lwb_t *nlwb = zil_lwb_write_issue(zilog, lwb);
    ASSERT3S(lwb->lwb_state, !=, LWB_STATE_OPENED);

In this case, if `dmu_tx_assign` returned `EIO` from within
`zil_lwb_write_issue`, the `lwb` variable passed in will not be issued
to disk. Thus, it's `lwb_state` field will remain `LWB_STATE_OPENED` and
this assertion will fail. `zil_commit_waiter_timeout` assumes that after
it calls `zil_lwb_write_issue`, the `lwb` will be issued to disk, and
doesn't handle the case where this is not true; i.e. it doesn't handle
the case where `dmu_tx_assign` returns `EIO`.

SOLUTION
========

This change modifies the `dmu_tx_assign` function such that `txg_how` is
a bitmask, rather than of the `txg_how_t` enum type. Now, the previous
`TXG_WAITED` semantics can be used via `TXG_NOTHROTTLE`, along with
specifying either `TXG_NOWAIT` or `TXG_WAIT` semantics.

Previously, when `TXG_WAITED` was specified, `TXG_NOWAIT` semantics was
automatically invoked. This was not ideal when using `TXG_WAITED` within
`zil_lwb_write_issued`, leading the problem described above. Rather, we
want to achieve the semantics of `TXG_WAIT`, while also preventing the
`tx` from being penalized via the dirty delay throttling.

With this change, `zil_lwb_write_issued` can acheive the semtantics that
it requires by passing in the value `TXG_WAIT | TXG_NOTHROTTLE` to
`dmu_tx_assign`.

Further, consumers of `dmu_tx_assign` wishing to achieve the old
`TXG_WAITED` semantics can pass in the value `TXG_NOWAIT | TXG_NOTHROTTLE`.

Authored by: Prakash Surya <prakash.surya@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Andriy Gapon <avg@FreeBSD.org>
Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>

Porting Notes:
- Additionally updated `zfs_tmpfile` to use `TXG_NOTHROTTLE`

OpenZFS-issue: https://www.illumos.org/issues/8997
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/19ea6cb0f9
Closes #7084
2018-07-06 02:46:51 -07:00
.github Update codecov.yml 2018-03-14 16:10:36 -07:00
cmd Fedora 28: Fix misc bounds check compiler warnings 2018-05-07 17:19:57 -07:00
config Linux compat 4.18: check_disk_size_change() 2018-07-06 02:46:51 -07:00
contrib modprobe zfs during dracut mount 2018-05-07 17:19:57 -07:00
etc chmod -x on etc/init.d/zfs-*.in automake files 2018-05-07 17:19:57 -07:00
include OpenZFS 8997 - ztest assertion failure in zil_lwb_write_issue 2018-07-06 02:46:51 -07:00
lib Linux 4.18 compat: inode timespec -> timespec64 2018-07-06 02:46:51 -07:00
man Add back iostat -y or -w descriptions 2018-05-07 17:19:57 -07:00
module OpenZFS 8997 - ztest assertion failure in zil_lwb_write_issue 2018-07-06 02:46:51 -07:00
rpm Tag zfs-0.7.9 2018-05-08 13:33:38 -07:00
scripts Fix free memory calculation on v3.14+ 2018-03-14 16:10:37 -07:00
tests Add test with two kinds of file creation orders 2018-05-07 17:19:57 -07:00
udev Fix spelling 2017-01-03 11:31:18 -06:00
.gitignore Add configure option to enable gcov analysis 2018-03-14 16:10:36 -07:00
.gitmodules Add zimport.sh compatibility test script 2014-02-21 12:10:31 -08:00
AUTHORS Add a missing > to AUTHORS 2014-09-02 14:18:53 -07:00
COPYRIGHT Update ZED copyright boilerplate 2015-05-11 15:07:00 -07:00
DISCLAIMER Fix minor typos and update marketing copy. 2013-03-21 12:51:06 -07:00
META Tag zfs-0.7.9 2018-05-08 13:33:38 -07:00
Makefile.am Add support for "--enable-code-coverage" option 2018-03-14 16:10:36 -07:00
OPENSOLARIS.LICENSE Add CDDL license file 2008-12-01 14:49:34 -08:00
README.markdown Update codecov.yml 2018-03-14 16:10:36 -07:00
TEST Retire filebench testing 2017-06-01 06:24:28 -07:00
autogen.sh build: do not call boilerplate ourself 2013-04-02 10:55:20 -07:00
configure.ac Fix mmap / libaio deadlock 2018-05-07 17:19:57 -07:00
copy-builtin Allow c99 when building ZFS in the kernel tree 2017-03-27 12:31:15 -07:00
zfs-script-config.sh.in zpool iostat/status -c improvements 2017-06-05 10:52:15 -07:00
zfs.release.in Move zfs.release generation to configure step 2012-07-12 12:22:51 -07:00

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