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bcachefs: Improve btree_deadlock debugfs output

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This changes bch2_check_for_deadlock() to print the longest chains it
finds - when we have a deadlock because the cycle detector isn't finding
something, this will let us see what it's missing.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2022-10-02 01:41:08 -04:00
parent 943f9946a6
commit 40a44873a5
2 changed files with 50 additions and 21 deletions
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54
fs/bcachefs/btree_locking.c
View File

@ -71,11 +71,6 @@ struct lock_graph {
unsigned nr;
};
static void lock_graph_pop(struct lock_graph *g)
{
closure_put(&g->g[--g->nr].trans->ref);
}
static noinline void print_cycle(struct printbuf *out, struct lock_graph *g)
{
struct trans_waiting_for_lock *i;
@ -87,6 +82,18 @@ static noinline void print_cycle(struct printbuf *out, struct lock_graph *g)
bch2_btree_trans_to_text(out, i->trans);
}
static noinline void print_chain(struct printbuf *out, struct lock_graph *g)
{
struct trans_waiting_for_lock *i;
for (i = g->g; i != g->g + g->nr; i++) {
if (i != g->g)
prt_str(out, "<- ");
prt_printf(out, "%u ", i->trans->locking_wait.task->pid);
}
prt_newline(out);
}
static int abort_lock(struct lock_graph *g, struct trans_waiting_for_lock *i)
{
int ret;
@ -134,6 +141,21 @@ static noinline int break_cycle(struct lock_graph *g)
BUG();
}
static void lock_graph_pop(struct lock_graph *g)
{
closure_put(&g->g[--g->nr].trans->ref);
}
static void lock_graph_pop_above(struct lock_graph *g, struct trans_waiting_for_lock *above,
struct printbuf *cycle)
{
if (g->nr > 1 && cycle)
print_chain(cycle, g);
while (g->g + g->nr > above)
lock_graph_pop(g);
}
static int lock_graph_descend(struct lock_graph *g, struct btree_trans *trans,
struct printbuf *cycle)
{
@ -142,11 +164,10 @@ static int lock_graph_descend(struct lock_graph *g, struct btree_trans *trans,
int ret = 0;
for (i = g->g; i < g->g + g->nr; i++) {
if (i->trans->locking != i->node_want)
while (g->g + g->nr >= i) {
lock_graph_pop(g);
return 0;
}
if (i->trans->locking != i->node_want) {
lock_graph_pop_above(g, i - 1, cycle);
return 0;
}
if (i->trans == trans) {
if (cycle) {
@ -185,20 +206,19 @@ static int lock_graph_descend(struct lock_graph *g, struct btree_trans *trans,
return 0;
deadlock:
while (g->nr)
lock_graph_pop(g);
lock_graph_pop_above(g, g->g, cycle);
return ret;
}
static noinline void lock_graph_remove_non_waiters(struct lock_graph *g)
static noinline void lock_graph_remove_non_waiters(struct lock_graph *g,
struct printbuf *cycle)
{
struct trans_waiting_for_lock *i;
for (i = g->g + 1; i < g->g + g->nr; i++)
if (i->trans->locking != i->node_want ||
i->trans->locking_wait.start_time != i[-1].lock_start_time) {
while (g->g + g->nr >= i)
lock_graph_pop(g);
lock_graph_pop_above(g, i - 1, cycle);
return;
}
BUG();
@ -252,7 +272,7 @@ int bch2_check_for_deadlock(struct btree_trans *trans, struct printbuf *cycle)
b = &READ_ONCE(path->l[top->level].b)->c;
if (unlikely(IS_ERR_OR_NULL(b))) {
lock_graph_remove_non_waiters(&g);
lock_graph_remove_non_waiters(&g, cycle);
goto next;
}
@ -286,6 +306,8 @@ int bch2_check_for_deadlock(struct btree_trans *trans, struct printbuf *cycle)
}
}
if (g.nr > 1 && cycle)
print_chain(cycle, &g);
lock_graph_pop(&g);
goto next;
}

17
fs/bcachefs/debug.c
View File

@ -725,11 +725,18 @@ static ssize_t bch2_btree_deadlock_read(struct file *file, char __user *buf,
goto out;
mutex_lock(&c->btree_trans_lock);
list_for_each_entry(trans, &c->btree_trans_list, list)
if (bch2_check_for_deadlock(trans, &i->buf)) {
i->iter = 1;
break;
}
list_for_each_entry(trans, &c->btree_trans_list, list) {
if (trans->locking_wait.task->pid <= i->iter)
continue;
ret = flush_buf(i);
if (ret)
return ret;
bch2_check_for_deadlock(trans, &i->buf);
i->iter = trans->locking_wait.task->pid;
}
mutex_unlock(&c->btree_trans_lock);
out:
if (i->buf.allocation_failure)