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Apr 1, 2025
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Be more careful about iterator invalidation during recursive invalida… #57934

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5 changes: 5 additions & 0 deletions Compiler/test/invalidation.jl
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Expand Up @@ -283,3 +283,8 @@ begin take!(GLOBAL_BUFFER)
@test isnothing(pr48932_caller_inlined(42))
@test "42" == String(take!(GLOBAL_BUFFER))
end

# Issue #57696
# This test checks for invalidation of recursive backedges. However, unfortunately, the original failure
# manifestation was an unreliable segfault or an assertion failure, so we don't have a more compact test.
@test success(`$(Base.julia_cmd()) -e 'Base.typejoin(x, ::Type) = 0; exit()'`)
237 changes: 134 additions & 103 deletions src/gf.c
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Expand Up @@ -1831,43 +1831,133 @@ JL_DLLEXPORT void jl_invalidate_code_instance(jl_code_instance_t *replaced, size
}

static void _invalidate_backedges(jl_method_instance_t *replaced_mi, jl_code_instance_t *replaced_ci, size_t max_world, int depth) {
jl_array_t *backedges = replaced_mi->backedges;
if (backedges) {
// invalidate callers (if any)
uint8_t recursion_flags = 0;
jl_array_t *backedges = jl_mi_get_backedges_mutate(replaced_mi, &recursion_flags);
if (!backedges)
return;
// invalidate callers (if any)
if (!replaced_ci) {
// We know all backedges are deleted - clear them eagerly
// Clears both array and flags
replaced_mi->backedges = NULL;
JL_GC_PUSH1(&backedges);
size_t i = 0, l = jl_array_nrows(backedges);
size_t ins = 0;
jl_code_instance_t *replaced;
while (i < l) {
jl_value_t *invokesig = NULL;
i = get_next_edge(backedges, i, &invokesig, &replaced);
JL_GC_PROMISE_ROOTED(replaced); // propagated by get_next_edge from backedges
if (replaced_ci) {
// If we're invalidating a particular codeinstance, only invalidate
// this backedge it actually has an edge for our codeinstance.
jl_svec_t *edges = jl_atomic_load_relaxed(&replaced->edges);
for (size_t j = 0; j < jl_svec_len(edges); ++j) {
jl_value_t *edge = jl_svecref(edges, j);
if (edge == (jl_value_t*)replaced_mi || edge == (jl_value_t*)replaced_ci)
goto found;
}
// Keep this entry in the backedge list, but compact it
ins = set_next_edge(backedges, ins, invokesig, replaced);
continue;
found:;
jl_atomic_fetch_and_relaxed(&replaced_mi->flags, ~MI_FLAG_BACKEDGES_ALL);
}
JL_GC_PUSH1(&backedges);
size_t i = 0, l = jl_array_nrows(backedges);
size_t ins = 0;
jl_code_instance_t *replaced;
while (i < l) {
jl_value_t *invokesig = NULL;
i = get_next_edge(backedges, i, &invokesig, &replaced);
if (!replaced) {
ins = i;
continue;
}
JL_GC_PROMISE_ROOTED(replaced); // propagated by get_next_edge from backedges
if (replaced_ci) {
// If we're invalidating a particular codeinstance, only invalidate
// this backedge it actually has an edge for our codeinstance.
jl_svec_t *edges = jl_atomic_load_relaxed(&replaced->edges);
for (size_t j = 0; j < jl_svec_len(edges); ++j) {
jl_value_t *edge = jl_svecref(edges, j);
if (edge == (jl_value_t*)replaced_mi || edge == (jl_value_t*)replaced_ci)
goto found;
}
invalidate_code_instance(replaced, max_world, depth);
ins = set_next_edge(backedges, ins, invokesig, replaced);
continue;
found:;
ins = clear_next_edge(backedges, ins, invokesig, replaced);
jl_atomic_fetch_or(&replaced_mi->flags, MI_FLAG_BACKEDGES_DIRTY);
/* fallthrough */
}
invalidate_code_instance(replaced, max_world, depth);
if (replaced_ci && !replaced_mi->backedges) {
// Fast-path early out. If `invalidate_code_instance` invalidated
// the entire mi via a recursive edge, there's no point to keep
// iterating - they'll already have been invalidated.
break;
}
if (replaced_ci && ins != 0) {
jl_array_del_end(backedges, l - ins);
// If we're only invalidating one ci, we don't know which ci any particular
// backedge was for, so we can't delete them. Put them back.
replaced_mi->backedges = backedges;
jl_gc_wb(replaced_mi, backedges);
}
if (replaced_ci)
jl_mi_done_backedges(replaced_mi, recursion_flags);
JL_GC_POP();
}

enum morespec_options {
morespec_unknown,
morespec_isnot,
morespec_is
};

// check if `type` is replacing `m` with an ambiguity here, given other methods in `d` that already match it
static int is_replacing(char ambig, jl_value_t *type, jl_method_t *m, jl_method_t *const *d, size_t n, jl_value_t *isect, jl_value_t *isect2, char *morespec)
{
size_t k;
for (k = 0; k < n; k++) {
jl_method_t *m2 = d[k];
// see if m2 also fully covered this intersection
if (m == m2 || !(jl_subtype(isect, m2->sig) || (isect2 && jl_subtype(isect2, m2->sig))))
continue;
if (morespec[k] == (char)morespec_unknown)
morespec[k] = (char)(jl_type_morespecific(m2->sig, type) ? morespec_is : morespec_isnot);
if (morespec[k] == (char)morespec_is)
// not actually shadowing this--m2 will still be better
return 0;
// if type is not more specific than m (thus now dominating it)
// then there is a new ambiguity here,
// since m2 was also a previous match over isect,
// see if m was previously dominant over all m2
// or if this was already ambiguous before
if (ambig != morespec_is && !jl_type_morespecific(m->sig, m2->sig)) {
// m and m2 were previously ambiguous over the full intersection of mi with type, and will still be ambiguous with addition of type
return 0;
}
JL_GC_POP();
}
return 1;
}

static int _invalidate_dispatch_backedges(jl_method_instance_t *mi, jl_value_t *type, jl_method_t *m,
jl_method_t *const *d, size_t n, int replaced_dispatch, int ambig,
size_t max_world, char *morespec)
{
uint8_t backedge_recursion_flags = 0;
jl_array_t *backedges = jl_mi_get_backedges_mutate(mi, &backedge_recursion_flags);
if (!backedges)
return 0;
size_t ib = 0, insb = 0, nb = jl_array_nrows(backedges);
jl_value_t *invokeTypes;
jl_code_instance_t *caller;
int invalidated_any = 0;
while (mi->backedges && ib < nb) {
ib = get_next_edge(backedges, ib, &invokeTypes, &caller);
if (!caller) {
insb = ib;
continue;
}
JL_GC_PROMISE_ROOTED(caller); // propagated by get_next_edge from backedges
int replaced_edge;
if (invokeTypes) {
// n.b. normally we must have mi.specTypes <: invokeTypes <: m.sig (though it might not strictly hold), so we only need to check the other subtypes
if (jl_egal(invokeTypes, jl_get_ci_mi(caller)->def.method->sig))
replaced_edge = 0; // if invokeTypes == m.sig, then the only way to change this invoke is to replace the method itself
else
replaced_edge = jl_subtype(invokeTypes, type) && is_replacing(ambig, type, m, d, n, invokeTypes, NULL, morespec);
}
else {
replaced_edge = replaced_dispatch;
}
if (replaced_edge) {
invalidate_code_instance(caller, max_world, 1);
insb = clear_next_edge(backedges, insb, invokeTypes, caller);
jl_atomic_fetch_or(&mi->flags, MI_FLAG_BACKEDGES_DIRTY);
invalidated_any = 1;
}
else {
insb = set_next_edge(backedges, insb, invokeTypes, caller);
}
}
jl_mi_done_backedges(mi, backedge_recursion_flags);
return invalidated_any;
}

// invalidate cached methods that overlap this definition
Expand Down Expand Up @@ -1898,20 +1988,22 @@ JL_DLLEXPORT void jl_method_instance_add_backedge(jl_method_instance_t *callee,
JL_LOCK(&callee->def.method->writelock);
if (jl_atomic_load_relaxed(&allow_new_worlds)) {
int found = 0;
jl_array_t *backedges = jl_mi_get_backedges(callee);
// TODO: use jl_cache_type_(invokesig) like cache_method does to save memory
if (!callee->backedges) {
if (!backedges) {
// lazy-init the backedges array
callee->backedges = jl_alloc_vec_any(0);
jl_gc_wb(callee, callee->backedges);
backedges = jl_alloc_vec_any(0);
callee->backedges = backedges;
jl_gc_wb(callee, backedges);
}
else {
size_t i = 0, l = jl_array_nrows(callee->backedges);
size_t i = 0, l = jl_array_nrows(backedges);
for (i = 0; i < l; i++) {
// optimized version of while (i < l) i = get_next_edge(callee->backedges, i, &invokeTypes, &mi);
jl_value_t *ciedge = jl_array_ptr_ref(callee->backedges, i);
jl_value_t *ciedge = jl_array_ptr_ref(backedges, i);
if (ciedge != (jl_value_t*)caller)
continue;
jl_value_t *invokeTypes = i > 0 ? jl_array_ptr_ref(callee->backedges, i - 1) : NULL;
jl_value_t *invokeTypes = i > 0 ? jl_array_ptr_ref(backedges, i - 1) : NULL;
if (invokeTypes && jl_is_method_instance(invokeTypes))
invokeTypes = NULL;
if ((invokesig == NULL && invokeTypes == NULL) ||
Expand All @@ -1922,7 +2014,7 @@ JL_DLLEXPORT void jl_method_instance_add_backedge(jl_method_instance_t *callee,
}
}
if (!found)
push_edge(callee->backedges, invokesig, caller);
push_edge(backedges, invokesig, caller);
}
JL_UNLOCK(&callee->def.method->writelock);
}
Expand Down Expand Up @@ -2111,13 +2203,13 @@ static int erase_method_backedges(jl_typemap_entry_t *def, void *closure)
for (i = 0; i < l; i++) {
jl_method_instance_t *mi = (jl_method_instance_t*)jl_svecref(specializations, i);
if ((jl_value_t*)mi != jl_nothing) {
mi->backedges = NULL;
mi->backedges = 0;
}
}
}
else {
jl_method_instance_t *mi = (jl_method_instance_t*)specializations;
mi->backedges = NULL;
mi->backedges = 0;
}
JL_UNLOCK(&method->writelock);
return 1;
Expand Down Expand Up @@ -2189,39 +2281,6 @@ static int jl_type_intersection2(jl_value_t *t1, jl_value_t *t2, jl_value_t **is
return 1;
}

enum morespec_options {
morespec_unknown,
morespec_isnot,
morespec_is
};

// check if `type` is replacing `m` with an ambiguity here, given other methods in `d` that already match it
static int is_replacing(char ambig, jl_value_t *type, jl_method_t *m, jl_method_t *const *d, size_t n, jl_value_t *isect, jl_value_t *isect2, char *morespec)
{
size_t k;
for (k = 0; k < n; k++) {
jl_method_t *m2 = d[k];
// see if m2 also fully covered this intersection
if (m == m2 || !(jl_subtype(isect, m2->sig) || (isect2 && jl_subtype(isect2, m2->sig))))
continue;
if (morespec[k] == (char)morespec_unknown)
morespec[k] = (char)(jl_type_morespecific(m2->sig, type) ? morespec_is : morespec_isnot);
if (morespec[k] == (char)morespec_is)
// not actually shadowing this--m2 will still be better
return 0;
// if type is not more specific than m (thus now dominating it)
// then there is a new ambiguity here,
// since m2 was also a previous match over isect,
// see if m was previously dominant over all m2
// or if this was already ambiguous before
if (ambig != morespec_is && !jl_type_morespecific(m->sig, m2->sig)) {
// m and m2 were previously ambiguous over the full intersection of mi with type, and will still be ambiguous with addition of type
return 0;
}
}
return 1;
}

jl_typemap_entry_t *jl_method_table_add(jl_methtable_t *mt, jl_method_t *method, jl_tupletype_t *simpletype)
{
JL_TIMING(ADD_METHOD, ADD_METHOD);
Expand Down Expand Up @@ -2386,35 +2445,7 @@ void jl_method_table_activate(jl_methtable_t *mt, jl_typemap_entry_t *newentry)
// found that this specialization dispatch got replaced by m
// call invalidate_backedges(mi, max_world, "jl_method_table_insert");
// but ignore invoke-type edges
jl_array_t *backedges = mi->backedges;
if (backedges) {
size_t ib = 0, insb = 0, nb = jl_array_nrows(backedges);
jl_value_t *invokeTypes;
jl_code_instance_t *caller;
while (ib < nb) {
ib = get_next_edge(backedges, ib, &invokeTypes, &caller);
JL_GC_PROMISE_ROOTED(caller); // propagated by get_next_edge from backedges
int replaced_edge;
if (invokeTypes) {
// n.b. normally we must have mi.specTypes <: invokeTypes <: m.sig (though it might not strictly hold), so we only need to check the other subtypes
if (jl_egal(invokeTypes, jl_get_ci_mi(caller)->def.method->sig))
replaced_edge = 0; // if invokeTypes == m.sig, then the only way to change this invoke is to replace the method itself
else
replaced_edge = jl_subtype(invokeTypes, type) && is_replacing(ambig, type, m, d, n, invokeTypes, NULL, morespec);
}
else {
replaced_edge = replaced_dispatch;
}
if (replaced_edge) {
invalidate_code_instance(caller, max_world, 1);
invalidated = 1;
}
else {
insb = set_next_edge(backedges, insb, invokeTypes, caller);
}
}
jl_array_del_end(backedges, nb - insb);
}
invalidated = _invalidate_dispatch_backedges(mi, type, m, d, n, replaced_dispatch, ambig, max_world, morespec);
jl_array_ptr_1d_push(oldmi, (jl_value_t*)mi);
if (_jl_debug_method_invalidation && invalidated) {
jl_array_ptr_1d_push(_jl_debug_method_invalidation, (jl_value_t*)mi);
Expand Down
5 changes: 4 additions & 1 deletion src/julia.h
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Expand Up @@ -404,13 +404,16 @@ struct _jl_method_instance_t {
} def; // pointer back to the context for this code
jl_value_t *specTypes; // argument types this was specialized for
jl_svec_t *sparam_vals; // static parameter values, indexed by def.method->sig
jl_array_t *backedges; // list of code-instances which call this method-instance; `invoke` records (invokesig, caller) pairs
// list of code-instances which call this method-instance; `invoke` records (invokesig, caller) pairs
jl_array_t *backedges;
_Atomic(struct _jl_code_instance_t*) cache;
uint8_t cache_with_orig; // !cache_with_specTypes

// flags for this method instance
// bit 0: generated by an explicit `precompile(...)`
// bit 1: dispatched
// bit 2: The ->backedges field is currently being walked higher up the stack - entries may be deleted, but not moved
// bit 3: The ->backedges field was modified and should be compacted when clearing bit 2
_Atomic(uint8_t) flags;
};
#define JL_MI_FLAGS_MASK_PRECOMPILED 0x01
Expand Down
20 changes: 20 additions & 0 deletions src/julia_internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -726,9 +726,29 @@ JL_DLLEXPORT void jl_resolve_definition_effects_in_ir(jl_array_t *stmts, jl_modu
JL_DLLEXPORT int jl_maybe_add_binding_backedge(jl_binding_t *b, jl_value_t *edge, jl_method_t *in_method);
JL_DLLEXPORT void jl_add_binding_backedge(jl_binding_t *b, jl_value_t *edge);

static const uint8_t MI_FLAG_BACKEDGES_INUSE = 0b0100;
static const uint8_t MI_FLAG_BACKEDGES_DIRTY = 0b1000;
static const uint8_t MI_FLAG_BACKEDGES_ALL = 0b1100;

STATIC_INLINE jl_array_t *jl_mi_get_backedges_mutate(jl_method_instance_t *mi JL_PROPAGATES_ROOT, uint8_t *flags) {
*flags = jl_atomic_load_relaxed(&mi->flags) & (MI_FLAG_BACKEDGES_ALL);
jl_array_t *ret = mi->backedges;
if (ret)
jl_atomic_fetch_or_relaxed(&mi->flags, MI_FLAG_BACKEDGES_INUSE);
return ret;
}

STATIC_INLINE jl_array_t *jl_mi_get_backedges(jl_method_instance_t *mi JL_PROPAGATES_ROOT) {
assert(!(jl_atomic_load_relaxed(&mi->flags) & MI_FLAG_BACKEDGES_ALL));
jl_array_t *ret = mi->backedges;
return ret;
}

int get_next_edge(jl_array_t *list, int i, jl_value_t** invokesig, jl_code_instance_t **caller) JL_NOTSAFEPOINT;
int set_next_edge(jl_array_t *list, int i, jl_value_t *invokesig, jl_code_instance_t *caller);
int clear_next_edge(jl_array_t *list, int i, jl_value_t *invokesig, jl_code_instance_t *caller);
void push_edge(jl_array_t *list, jl_value_t *invokesig, jl_code_instance_t *caller);
void jl_mi_done_backedges(jl_method_instance_t *mi JL_PROPAGATES_ROOT, uint8_t old_flags);

JL_DLLEXPORT void jl_add_method_root(jl_method_t *m, jl_module_t *mod, jl_value_t* root);
void jl_append_method_roots(jl_method_t *m, uint64_t modid, jl_array_t* roots);
Expand Down
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