Re: [PATCH 09/10] writeback: factor out wb_dirty_exceeded to remove repeated code

From: Dan Carpenter
Date: Tue Apr 30 2024 - 03:24:45 EST

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Hi Kemeng,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url: https://github.com/intel-lab-lkp/linux/commits/Kemeng-Shi/writeback-factor-out-wb_bg_dirty_limits-to-remove-repeated-code/20240429-114903
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link: https://lore.kernel.org/r/20240429034738.138609-10-shikemeng%40huaweicloud.com
patch subject: [PATCH 09/10] writeback: factor out wb_dirty_exceeded to remove repeated code
config: i386-randconfig-141-20240429 (https://download.01.org/0day-ci/archive/20240430/202404300231.bnb28iB8-lkp@xxxxxxxxx/config)
compiler: gcc-13 (Ubuntu 13.2.0-4ubuntu3) 13.2.0

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
| Closes: https://lore.kernel.org/r/202404300231.bnb28iB8-lkp@xxxxxxxxx/

New smatch warnings:
mm/page-writeback.c:1903 balance_dirty_pages() error: we previously assumed 'mdtc' could be null (see line 1886)

vim +/mdtc +1903 mm/page-writeback.c

fe6c9c6e3e3e33 Jan Kara 2022-06-23 1800 static int balance_dirty_pages(struct bdi_writeback *wb,
fe6c9c6e3e3e33 Jan Kara 2022-06-23 1801 unsigned long pages_dirtied, unsigned int flags)
^1da177e4c3f41 Linus Torvalds 2005-04-16 1802 {
2bc00aef030f4f Tejun Heo 2015-05-22 1803 struct dirty_throttle_control gdtc_stor = { GDTC_INIT(wb) };
c2aa723a609363 Tejun Heo 2015-05-22 1804 struct dirty_throttle_control mdtc_stor = { MDTC_INIT(wb, &gdtc_stor) };
2bc00aef030f4f Tejun Heo 2015-05-22 1805 struct dirty_throttle_control * const gdtc = &gdtc_stor;
c2aa723a609363 Tejun Heo 2015-05-22 1806 struct dirty_throttle_control * const mdtc = mdtc_valid(&mdtc_stor) ?
c2aa723a609363 Tejun Heo 2015-05-22 1807 &mdtc_stor : NULL;
c2aa723a609363 Tejun Heo 2015-05-22 1808 struct dirty_throttle_control *sdtc;
c8a7ee1b73042a Kemeng Shi 2024-04-23 1809 unsigned long nr_dirty;
83712358ba0a14 Wu Fengguang 2011-06-11 1810 long period;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1811 long pause;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1812 long max_pause;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1813 long min_pause;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1814 int nr_dirtied_pause;
143dfe8611a630 Wu Fengguang 2010-08-27 1815 unsigned long task_ratelimit;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1816 unsigned long dirty_ratelimit;
dfb8ae56783542 Tejun Heo 2015-05-22 1817 struct backing_dev_info *bdi = wb->bdi;
5a53748568f796 Maxim Patlasov 2013-09-11 1818 bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
e98be2d599207c Wu Fengguang 2010-08-29 1819 unsigned long start_time = jiffies;
fe6c9c6e3e3e33 Jan Kara 2022-06-23 1820 int ret = 0;
^1da177e4c3f41 Linus Torvalds 2005-04-16 1821
^1da177e4c3f41 Linus Torvalds 2005-04-16 1822 for (;;) {
83712358ba0a14 Wu Fengguang 2011-06-11 1823 unsigned long now = jiffies;
83712358ba0a14 Wu Fengguang 2011-06-11 1824
c8a7ee1b73042a Kemeng Shi 2024-04-23 1825 nr_dirty = global_node_page_state(NR_FILE_DIRTY);
5fce25a9df4865 Peter Zijlstra 2007-11-14 1826
204c26b42a22b8 Kemeng Shi 2024-04-29 1827 balance_domain_limits(gdtc, strictlimit);
204c26b42a22b8 Kemeng Shi 2024-04-29 1828 if (mdtc)
c2aa723a609363 Tejun Heo 2015-05-22 1829 /*
c2aa723a609363 Tejun Heo 2015-05-22 1830 * If @wb belongs to !root memcg, repeat the same
c2aa723a609363 Tejun Heo 2015-05-22 1831 * basic calculations for the memcg domain.
c2aa723a609363 Tejun Heo 2015-05-22 1832 */
204c26b42a22b8 Kemeng Shi 2024-04-29 1833 balance_domain_limits(mdtc, strictlimit);
5a53748568f796 Maxim Patlasov 2013-09-11 1834
ea6813be07dcdc Jan Kara 2022-06-23 1835 /*
ea6813be07dcdc Jan Kara 2022-06-23 1836 * In laptop mode, we wait until hitting the higher threshold
ea6813be07dcdc Jan Kara 2022-06-23 1837 * before starting background writeout, and then write out all
ea6813be07dcdc Jan Kara 2022-06-23 1838 * the way down to the lower threshold. So slow writers cause
ea6813be07dcdc Jan Kara 2022-06-23 1839 * minimal disk activity.
ea6813be07dcdc Jan Kara 2022-06-23 1840 *
ea6813be07dcdc Jan Kara 2022-06-23 1841 * In normal mode, we start background writeout at the lower
ea6813be07dcdc Jan Kara 2022-06-23 1842 * background_thresh, to keep the amount of dirty memory low.
ea6813be07dcdc Jan Kara 2022-06-23 1843 */
c8a7ee1b73042a Kemeng Shi 2024-04-23 1844 if (!laptop_mode && nr_dirty > gdtc->bg_thresh &&
ea6813be07dcdc Jan Kara 2022-06-23 1845 !writeback_in_progress(wb))
ea6813be07dcdc Jan Kara 2022-06-23 1846 wb_start_background_writeback(wb);
ea6813be07dcdc Jan Kara 2022-06-23 1847
16c4042f08919f Wu Fengguang 2010-08-11 1848 /*
c2aa723a609363 Tejun Heo 2015-05-22 1849 * If memcg domain is in effect, @dirty should be under
c2aa723a609363 Tejun Heo 2015-05-22 1850 * both global and memcg freerun ceilings.
16c4042f08919f Wu Fengguang 2010-08-11 1851 */
c474a90dc076a7 Kemeng Shi 2024-04-29 1852 if (gdtc->freerun && (!mdtc || mdtc->freerun)) {
a37b0715ddf300 NeilBrown 2020-06-01 1853 unsigned long intv;
a37b0715ddf300 NeilBrown 2020-06-01 1854 unsigned long m_intv;
a37b0715ddf300 NeilBrown 2020-06-01 1855
a37b0715ddf300 NeilBrown 2020-06-01 1856 free_running:
c474a90dc076a7 Kemeng Shi 2024-04-29 1857 intv = domain_poll_intv(gdtc, strictlimit);
a37b0715ddf300 NeilBrown 2020-06-01 1858 m_intv = ULONG_MAX;
c2aa723a609363 Tejun Heo 2015-05-22 1859
83712358ba0a14 Wu Fengguang 2011-06-11 1860 current->dirty_paused_when = now;
83712358ba0a14 Wu Fengguang 2011-06-11 1861 current->nr_dirtied = 0;
c2aa723a609363 Tejun Heo 2015-05-22 1862 if (mdtc)
c474a90dc076a7 Kemeng Shi 2024-04-29 1863 m_intv = domain_poll_intv(mdtc, strictlimit);
c2aa723a609363 Tejun Heo 2015-05-22 1864 current->nr_dirtied_pause = min(intv, m_intv);
16c4042f08919f Wu Fengguang 2010-08-11 1865 break;
83712358ba0a14 Wu Fengguang 2011-06-11 1866 }
16c4042f08919f Wu Fengguang 2010-08-11 1867
ea6813be07dcdc Jan Kara 2022-06-23 1868 /* Start writeback even when in laptop mode */
bc05873dccd27d Tejun Heo 2015-05-22 1869 if (unlikely(!writeback_in_progress(wb)))
9ecf4866c018ae Tejun Heo 2015-05-22 1870 wb_start_background_writeback(wb);
143dfe8611a630 Wu Fengguang 2010-08-27 1871
97b27821b4854c Tejun Heo 2019-08-26 1872 mem_cgroup_flush_foreign(wb);
97b27821b4854c Tejun Heo 2019-08-26 1873
c2aa723a609363 Tejun Heo 2015-05-22 1874 /*
c2aa723a609363 Tejun Heo 2015-05-22 1875 * Calculate global domain's pos_ratio and select the
c2aa723a609363 Tejun Heo 2015-05-22 1876 * global dtc by default.
c2aa723a609363 Tejun Heo 2015-05-22 1877 */
aab09fbaa2dd34 Kemeng Shi 2024-04-29 1878 wb_dirty_freerun(gdtc, strictlimit);
aab09fbaa2dd34 Kemeng Shi 2024-04-29 1879 if (gdtc->freerun)
a37b0715ddf300 NeilBrown 2020-06-01 1880 goto free_running;
a37b0715ddf300 NeilBrown 2020-06-01 1881
8b8bf84233eccf Kemeng Shi 2024-04-29 1882 wb_dirty_exceeded(gdtc, strictlimit);
daddfa3cb30ebf Tejun Heo 2015-05-22 1883 wb_position_ratio(gdtc);
c2aa723a609363 Tejun Heo 2015-05-22 1884 sdtc = gdtc;
e98be2d599207c Wu Fengguang 2010-08-29 1885
c2aa723a609363 Tejun Heo 2015-05-22 @1886 if (mdtc) {
^^^^^^^^^^^
This code assumes mdtc can be NULL

c2aa723a609363 Tejun Heo 2015-05-22 1887 /*
c2aa723a609363 Tejun Heo 2015-05-22 1888 * If memcg domain is in effect, calculate its
c2aa723a609363 Tejun Heo 2015-05-22 1889 * pos_ratio. @wb should satisfy constraints from
c2aa723a609363 Tejun Heo 2015-05-22 1890 * both global and memcg domains. Choose the one
c2aa723a609363 Tejun Heo 2015-05-22 1891 * w/ lower pos_ratio.
c2aa723a609363 Tejun Heo 2015-05-22 1892 */
aab09fbaa2dd34 Kemeng Shi 2024-04-29 1893 wb_dirty_freerun(mdtc, strictlimit);
aab09fbaa2dd34 Kemeng Shi 2024-04-29 1894 if (mdtc->freerun)
a37b0715ddf300 NeilBrown 2020-06-01 1895 goto free_running;
aab09fbaa2dd34 Kemeng Shi 2024-04-29 1896
8b8bf84233eccf Kemeng Shi 2024-04-29 1897 wb_dirty_exceeded(mdtc, strictlimit);
c2aa723a609363 Tejun Heo 2015-05-22 1898 wb_position_ratio(mdtc);
c2aa723a609363 Tejun Heo 2015-05-22 1899 if (mdtc->pos_ratio < gdtc->pos_ratio)
c2aa723a609363 Tejun Heo 2015-05-22 1900 sdtc = mdtc;
c2aa723a609363 Tejun Heo 2015-05-22 1901 }
daddfa3cb30ebf Tejun Heo 2015-05-22 1902
8b8bf84233eccf Kemeng Shi 2024-04-29 @1903 wb->dirty_exceeded = gdtc->dirty_exceeded || mdtc->dirty_exceeded;
^^^^^^
Unchecked dereference

20792ebf3eeb82 Jan Kara 2021-09-02 1904 if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) +
45a2966fd64147 Jan Kara 2021-09-02 1905 BANDWIDTH_INTERVAL))
fee468fdf41cdf Jan Kara 2021-09-02 1906 __wb_update_bandwidth(gdtc, mdtc, true);
e98be2d599207c Wu Fengguang 2010-08-29 1907
c2aa723a609363 Tejun Heo 2015-05-22 1908 /* throttle according to the chosen dtc */
20792ebf3eeb82 Jan Kara 2021-09-02 1909 dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit);
c2aa723a609363 Tejun Heo 2015-05-22 1910 task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >>
3a73dbbc9bb3fc Wu Fengguang 2011-11-07 1911 RATELIMIT_CALC_SHIFT;
c2aa723a609363 Tejun Heo 2015-05-22 1912 max_pause = wb_max_pause(wb, sdtc->wb_dirty);
a88a341a73be4e Tejun Heo 2015-05-22 1913 min_pause = wb_min_pause(wb, max_pause,
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1914 task_ratelimit, dirty_ratelimit,
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1915 &nr_dirtied_pause);
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1916
3a73dbbc9bb3fc Wu Fengguang 2011-11-07 1917 if (unlikely(task_ratelimit == 0)) {
83712358ba0a14 Wu Fengguang 2011-06-11 1918 period = max_pause;
c8462cc9de9e92 Wu Fengguang 2011-06-11 1919 pause = max_pause;
143dfe8611a630 Wu Fengguang 2010-08-27 1920 goto pause;
e50e37201ae2e7 Wu Fengguang 2010-08-11 1921 }
83712358ba0a14 Wu Fengguang 2011-06-11 1922 period = HZ * pages_dirtied / task_ratelimit;
83712358ba0a14 Wu Fengguang 2011-06-11 1923 pause = period;
83712358ba0a14 Wu Fengguang 2011-06-11 1924 if (current->dirty_paused_when)
83712358ba0a14 Wu Fengguang 2011-06-11 1925 pause -= now - current->dirty_paused_when;
83712358ba0a14 Wu Fengguang 2011-06-11 1926 /*
83712358ba0a14 Wu Fengguang 2011-06-11 1927 * For less than 1s think time (ext3/4 may block the dirtier
83712358ba0a14 Wu Fengguang 2011-06-11 1928 * for up to 800ms from time to time on 1-HDD; so does xfs,
83712358ba0a14 Wu Fengguang 2011-06-11 1929 * however at much less frequency), try to compensate it in
83712358ba0a14 Wu Fengguang 2011-06-11 1930 * future periods by updating the virtual time; otherwise just
83712358ba0a14 Wu Fengguang 2011-06-11 1931 * do a reset, as it may be a light dirtier.
83712358ba0a14 Wu Fengguang 2011-06-11 1932 */
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1933 if (pause < min_pause) {
5634cc2aa9aebc Tejun Heo 2015-08-18 1934 trace_balance_dirty_pages(wb,
c2aa723a609363 Tejun Heo 2015-05-22 1935 sdtc->thresh,
c2aa723a609363 Tejun Heo 2015-05-22 1936 sdtc->bg_thresh,
c2aa723a609363 Tejun Heo 2015-05-22 1937 sdtc->dirty,
c2aa723a609363 Tejun Heo 2015-05-22 1938 sdtc->wb_thresh,
c2aa723a609363 Tejun Heo 2015-05-22 1939 sdtc->wb_dirty,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1940 dirty_ratelimit,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1941 task_ratelimit,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1942 pages_dirtied,
83712358ba0a14 Wu Fengguang 2011-06-11 1943 period,
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1944 min(pause, 0L),
ece13ac31bbe49 Wu Fengguang 2010-08-29 1945 start_time);
83712358ba0a14 Wu Fengguang 2011-06-11 1946 if (pause < -HZ) {
83712358ba0a14 Wu Fengguang 2011-06-11 1947 current->dirty_paused_when = now;
83712358ba0a14 Wu Fengguang 2011-06-11 1948 current->nr_dirtied = 0;
83712358ba0a14 Wu Fengguang 2011-06-11 1949 } else if (period) {
83712358ba0a14 Wu Fengguang 2011-06-11 1950 current->dirty_paused_when += period;
83712358ba0a14 Wu Fengguang 2011-06-11 1951 current->nr_dirtied = 0;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1952 } else if (current->nr_dirtied_pause <= pages_dirtied)
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1953 current->nr_dirtied_pause += pages_dirtied;
57fc978cfb61ed Wu Fengguang 2011-06-11 1954 break;
e50e37201ae2e7 Wu Fengguang 2010-08-11 1955 }
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1956 if (unlikely(pause > max_pause)) {
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1957 /* for occasional dropped task_ratelimit */
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1958 now += min(pause - max_pause, max_pause);
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1959 pause = max_pause;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1960 }
143dfe8611a630 Wu Fengguang 2010-08-27 1961
143dfe8611a630 Wu Fengguang 2010-08-27 1962 pause:
5634cc2aa9aebc Tejun Heo 2015-08-18 1963 trace_balance_dirty_pages(wb,
c2aa723a609363 Tejun Heo 2015-05-22 1964 sdtc->thresh,
c2aa723a609363 Tejun Heo 2015-05-22 1965 sdtc->bg_thresh,
c2aa723a609363 Tejun Heo 2015-05-22 1966 sdtc->dirty,
c2aa723a609363 Tejun Heo 2015-05-22 1967 sdtc->wb_thresh,
c2aa723a609363 Tejun Heo 2015-05-22 1968 sdtc->wb_dirty,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1969 dirty_ratelimit,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1970 task_ratelimit,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1971 pages_dirtied,
83712358ba0a14 Wu Fengguang 2011-06-11 1972 period,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1973 pause,
ece13ac31bbe49 Wu Fengguang 2010-08-29 1974 start_time);
fe6c9c6e3e3e33 Jan Kara 2022-06-23 1975 if (flags & BDP_ASYNC) {
fe6c9c6e3e3e33 Jan Kara 2022-06-23 1976 ret = -EAGAIN;
fe6c9c6e3e3e33 Jan Kara 2022-06-23 1977 break;
fe6c9c6e3e3e33 Jan Kara 2022-06-23 1978 }
499d05ecf990a7 Jan Kara 2011-11-16 1979 __set_current_state(TASK_KILLABLE);
f814bdda774c18 Jan Kara 2024-01-23 1980 bdi->last_bdp_sleep = jiffies;
d25105e8911bff Wu Fengguang 2009-10-09 1981 io_schedule_timeout(pause);
87c6a9b253520b Jens Axboe 2009-09-17 1982
83712358ba0a14 Wu Fengguang 2011-06-11 1983 current->dirty_paused_when = now + pause;
83712358ba0a14 Wu Fengguang 2011-06-11 1984 current->nr_dirtied = 0;
7ccb9ad5364d6a Wu Fengguang 2011-11-30 1985 current->nr_dirtied_pause = nr_dirtied_pause;
83712358ba0a14 Wu Fengguang 2011-06-11 1986
ffd1f609ab1053 Wu Fengguang 2011-06-19 1987 /*
2bc00aef030f4f Tejun Heo 2015-05-22 1988 * This is typically equal to (dirty < thresh) and can also
2bc00aef030f4f Tejun Heo 2015-05-22 1989 * keep "1000+ dd on a slow USB stick" under control.
ffd1f609ab1053 Wu Fengguang 2011-06-19 1990 */
1df647197c5b8a Wu Fengguang 2011-11-13 1991 if (task_ratelimit)
ffd1f609ab1053 Wu Fengguang 2011-06-19 1992 break;
499d05ecf990a7 Jan Kara 2011-11-16 1993
c5c6343c4d75f9 Wu Fengguang 2011-12-02 1994 /*
f0953a1bbaca71 Ingo Molnar 2021-05-06 1995 * In the case of an unresponsive NFS server and the NFS dirty
de1fff37b2781f Tejun Heo 2015-05-22 1996 * pages exceeds dirty_thresh, give the other good wb's a pipe
c5c6343c4d75f9 Wu Fengguang 2011-12-02 1997 * to go through, so that tasks on them still remain responsive.
c5c6343c4d75f9 Wu Fengguang 2011-12-02 1998 *
3f8b6fb7f279c7 Masahiro Yamada 2017-02-27 1999 * In theory 1 page is enough to keep the consumer-producer
c5c6343c4d75f9 Wu Fengguang 2011-12-02 2000 * pipe going: the flusher cleans 1 page => the task dirties 1
de1fff37b2781f Tejun Heo 2015-05-22 2001 * more page. However wb_dirty has accounting errors. So use
93f78d882865cb Tejun Heo 2015-05-22 2002 * the larger and more IO friendly wb_stat_error.
c5c6343c4d75f9 Wu Fengguang 2011-12-02 2003 */
2bce774e8245e9 Wang Long 2017-11-15 2004 if (sdtc->wb_dirty <= wb_stat_error())
c5c6343c4d75f9 Wu Fengguang 2011-12-02 2005 break;
c5c6343c4d75f9 Wu Fengguang 2011-12-02 2006
499d05ecf990a7 Jan Kara 2011-11-16 2007 if (fatal_signal_pending(current))
499d05ecf990a7 Jan Kara 2011-11-16 2008 break;
^1da177e4c3f41 Linus Torvalds 2005-04-16 2009 }
fe6c9c6e3e3e33 Jan Kara 2022-06-23 2010 return ret;
^1da177e4c3f41 Linus Torvalds 2005-04-16 2011 }

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