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copy: improve state barriers

This commit is contained in:
Thomas Schoebel-Theuer 2022-02-22 06:06:39 +01:00 committed by Thomas Schoebel-Theuer
parent 7c59774177
commit e273447add
1 changed files with 23 additions and 9 deletions
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32
kernel/mars_copy.c
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@ -190,6 +190,9 @@ void _clear_mref(struct copy_brick *brick, unsigned index, unsigned queue)
index, queue); index, queue);
} }
__clear_mref(brick, mref, queue); __clear_mref(brick, mref, queue);
/* For safety, we had kept the reference across the INPUT_CALL().
* Now we should be safe to clean it.
*/
WRITE_ONCE(st->table[queue], NULL); WRITE_ONCE(st->table[queue], NULL);
} }
} }
@ -206,6 +209,10 @@ void _clear_all_mref(struct copy_brick *brick)
_clear_mref(brick, i, 0); _clear_mref(brick, i, 0);
_clear_mref(brick, i, 1); _clear_mref(brick, i, 1);
} }
/* Just for safety. Although _clear_mref() already used WRITE_ONCE().
* Sometimes, we mistrust the hardware ;)
*/
smp_mb();
} }
static static
@ -218,7 +225,8 @@ void _clear_state_table(struct copy_brick *brick)
memset(sub_table, 0, PAGE_SIZE); memset(sub_table, 0, PAGE_SIZE);
} }
mb(); /* just for safety. */
smp_mb();
} }
static static
@ -557,7 +565,7 @@ int _next_state(struct copy_brick *brick, unsigned index, loff_t pos,
int status; int status;
st = _GET_STATE(brick, index); st = _GET_STATE(brick, index);
next_state = st->state; next_state = READ_ONCE(st->state);
restart: restart:
state = next_state; state = next_state;
@ -633,7 +641,7 @@ restart:
goto idle; goto idle;
} }
st->writeout = false; WRITE_ONCE(st->writeout, false);
WRITE_ONCE(st->error, 0); WRITE_ONCE(st->error, 0);
if (brick->is_aborting || if (brick->is_aborting ||
@ -833,7 +841,7 @@ restart:
MARS_IO("irrelevant\n"); MARS_IO("irrelevant\n");
goto idle; goto idle;
} }
st->writeout = true; WRITE_ONCE(st->writeout, true);
/* rechecking means to start over again. /* rechecking means to start over again.
* ATTENTIION! this may lead to infinite request * ATTENTIION! this may lead to infinite request
* submission loops, intentionally. * submission loops, intentionally.
@ -869,6 +877,12 @@ restart:
idle: idle:
if (unlikely(progress < 0)) { if (unlikely(progress < 0)) {
/* Subtle race here:
* We don't lock or use atomics or cmpxchg or sisters,
* because (a) the reason for any error does not really matter,
* and (b) the progress should be regarded as a _hint_
* (not contributing to the logic).
*/
if (READ_ONCE(st->error) >= 0) if (READ_ONCE(st->error) >= 0)
WRITE_ONCE(st->error, progress); WRITE_ONCE(st->error, progress);
MARS_DBG("progress = %d\n", progress); MARS_DBG("progress = %d\n", progress);
@ -876,7 +890,7 @@ idle:
notify_clash(brick); notify_clash(brick);
} else if (do_restart) { } else if (do_restart) {
goto restart; goto restart;
} else if (st->state != next_state) { } else if (READ_ONCE(st->state) != next_state) {
progress++; progress++;
} }
@ -894,7 +908,7 @@ idle:
progress); progress);
// save the resulting state // save the resulting state
st->state = next_state; WRITE_ONCE(st->state, next_state);
return progress; return progress;
} }
@ -983,7 +997,7 @@ int _run_copy(struct copy_brick *brick, loff_t this_start)
struct copy_state *st = _GET_STATE(brick, index); struct copy_state *st = _GET_STATE(brick, index);
bool is_active; bool is_active;
if (st->state != COPY_STATE_FINISHED) { if (READ_ONCE(st->state) != COPY_STATE_FINISHED) {
break; break;
} }
if (max-- <= 0) { if (max-- <= 0) {
@ -1017,8 +1031,8 @@ int _run_copy(struct copy_brick *brick, loff_t this_start)
break; break;
} }
// rollover // rollover
st->state = COPY_STATE_START; WRITE_ONCE(st->state, COPY_STATE_START);
len = st->len; len = READ_ONCE(st->len);
count += len; count += len;
// check contiguity // check contiguity
if (unlikely(GET_OFFSET(pos) + len != COPY_CHUNK)) { if (unlikely(GET_OFFSET(pos) + len != COPY_CHUNK)) {