diff options
author | Jan Kara <jack@suse.cz> | 2021-07-30 16:09:08 +0100 |
---|---|---|
committer | Mark Brown <broonie@kernel.org> | 2021-07-30 16:09:08 +0100 |
commit | d666b327d149f2f5c2287fd0e84c6a31cf7cb28e (patch) | |
tree | 18a779ad45e7e8fc2e233caf7506039c6e21e273 | |
parent | e09a1a407d22cace3c781640b5fe154f398ae98b (diff) | |
download | linux-2.6-d666b327d149f2f5c2287fd0e84c6a31cf7cb28e.tar.gz |
writeback: use READ_ONCE for unlocked reads of writeback stats
We do some unlocked reads of writeback statistics like
avg_write_bandwidth, dirty_ratelimit, or bw_time_stamp. Generally we are
fine with getting somewhat out-of-date values but actually getting
different values in various parts of the functions because the compiler
decided to reload value from original memory location could confuse
calculations. Use READ_ONCE for these unlocked accesses and WRITE_ONCE
for the updates to be on the safe side.
Link: https://lkml.kernel.org/r/20210713104716.22868-5-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Michael Stapelberg <stapelberg+linux@google.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
-rw-r--r-- | mm/page-writeback.c | 28 |
1 files changed, 15 insertions, 13 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index ae5ace94e86eea..57b98ea365e27b 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -183,7 +183,7 @@ static struct fprop_local_percpu *wb_memcg_completions(struct bdi_writeback *wb) static void wb_min_max_ratio(struct bdi_writeback *wb, unsigned long *minp, unsigned long *maxp) { - unsigned long this_bw = wb->avg_write_bandwidth; + unsigned long this_bw = READ_ONCE(wb->avg_write_bandwidth); unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth); unsigned long long min = wb->bdi->min_ratio; unsigned long long max = wb->bdi->max_ratio; @@ -892,7 +892,7 @@ static long long pos_ratio_polynom(unsigned long setpoint, static void wb_position_ratio(struct dirty_throttle_control *dtc) { struct bdi_writeback *wb = dtc->wb; - unsigned long write_bw = wb->avg_write_bandwidth; + unsigned long write_bw = READ_ONCE(wb->avg_write_bandwidth); unsigned long freerun = dirty_freerun_ceiling(dtc->thresh, dtc->bg_thresh); unsigned long limit = hard_dirty_limit(dtc_dom(dtc), dtc->thresh); unsigned long wb_thresh = dtc->wb_thresh; @@ -1115,7 +1115,7 @@ out: &wb->bdi->tot_write_bandwidth) <= 0); } wb->write_bandwidth = bw; - wb->avg_write_bandwidth = avg; + WRITE_ONCE(wb->avg_write_bandwidth, avg); } static void update_dirty_limit(struct dirty_throttle_control *dtc) @@ -1324,7 +1324,7 @@ static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc, else dirty_ratelimit -= step; - wb->dirty_ratelimit = max(dirty_ratelimit, 1UL); + WRITE_ONCE(wb->dirty_ratelimit, max(dirty_ratelimit, 1UL)); wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit; trace_bdi_dirty_ratelimit(wb, dirty_rate, task_ratelimit); @@ -1336,11 +1336,12 @@ static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc, { struct bdi_writeback *wb = gdtc->wb; unsigned long now = jiffies; - unsigned long elapsed = now - wb->bw_time_stamp; + unsigned long elapsed; unsigned long dirtied; unsigned long written; spin_lock(&wb->list_lock); + elapsed = now - wb->bw_time_stamp; dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]); written = percpu_counter_read(&wb->stat[WB_WRITTEN]); @@ -1361,7 +1362,7 @@ static void __wb_update_bandwidth(struct dirty_throttle_control *gdtc, wb->dirtied_stamp = dirtied; wb->written_stamp = written; - wb->bw_time_stamp = now; + WRITE_ONCE(wb->bw_time_stamp, now); spin_unlock(&wb->list_lock); } @@ -1385,7 +1386,7 @@ static void wb_bandwidth_estimate_start(struct bdi_writeback *wb) spin_lock(&wb->list_lock); wb->dirtied_stamp = wb_stat(wb, WB_DIRTIED); wb->written_stamp = wb_stat(wb, WB_WRITTEN); - wb->bw_time_stamp = now; + WRITE_ONCE(wb->bw_time_stamp, now); spin_unlock(&wb->list_lock); } } @@ -1410,7 +1411,7 @@ static unsigned long dirty_poll_interval(unsigned long dirty, static unsigned long wb_max_pause(struct bdi_writeback *wb, unsigned long wb_dirty) { - unsigned long bw = wb->avg_write_bandwidth; + unsigned long bw = READ_ONCE(wb->avg_write_bandwidth); unsigned long t; /* @@ -1432,8 +1433,8 @@ static long wb_min_pause(struct bdi_writeback *wb, unsigned long dirty_ratelimit, int *nr_dirtied_pause) { - long hi = ilog2(wb->avg_write_bandwidth); - long lo = ilog2(wb->dirty_ratelimit); + long hi = ilog2(READ_ONCE(wb->avg_write_bandwidth)); + long lo = ilog2(READ_ONCE(wb->dirty_ratelimit)); long t; /* target pause */ long pause; /* estimated next pause */ int pages; /* target nr_dirtied_pause */ @@ -1713,12 +1714,12 @@ free_running: if (dirty_exceeded && !wb->dirty_exceeded) wb->dirty_exceeded = 1; - if (time_is_before_jiffies(wb->bw_time_stamp + + if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) + BANDWIDTH_INTERVAL)) __wb_update_bandwidth(gdtc, mdtc, true); /* throttle according to the chosen dtc */ - dirty_ratelimit = wb->dirty_ratelimit; + dirty_ratelimit = READ_ONCE(wb->dirty_ratelimit); task_ratelimit = ((u64)dirty_ratelimit * sdtc->pos_ratio) >> RATELIMIT_CALC_SHIFT; max_pause = wb_max_pause(wb, sdtc->wb_dirty); @@ -2368,7 +2369,8 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc) * but if there's constant writeback being submitted, this makes sure * writeback bandwidth is updated once in a while. */ - if (time_is_before_jiffies(wb->bw_time_stamp + BANDWIDTH_INTERVAL)) + if (time_is_before_jiffies(READ_ONCE(wb->bw_time_stamp) + + BANDWIDTH_INTERVAL)) wb_update_bandwidth(wb); return ret; } |