[PATCH v7 3/4] perf symbol-elf: dso__load_sym_internal reference count fixes

[Ian Rogers]

dso__load_sym_internal passed curr_mapp as an out argument to
dso__process_kernel_symbol. The out argument was never used so remove
it to simplify the reference counting logic.

Simplify reference counting issues with curr_dso by ensuring the value
it points to has a +1 reference count, and then putting as
necessary. This avoids some reference counting games when the dso is
created making the code more obviously correct with some possible
introduced overhead due to the reference counting get/puts. This,
however, silences reference count checking and we can always optimize
from a seemingly correct point.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/symbol-elf.c | 51 ++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 26 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 3be5e8d1e278..e398abfd13a0 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1419,7 +1419,7 @@ void __weak arch__sym_update(struct symbol *s __maybe_unused,
 static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
 				      GElf_Sym *sym, GElf_Shdr *shdr,
 				      struct maps *kmaps, struct kmap *kmap,
-				      struct dso **curr_dsop, struct map **curr_mapp,
+				      struct dso **curr_dsop,
 				      const char *section_name,
 				      bool adjust_kernel_syms, bool kmodule, bool *remap_kernel,
 				      u64 max_text_sh_offset)
@@ -1470,8 +1470,8 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
 			map__set_pgoff(map, shdr->sh_offset);
 		}
 
-		*curr_mapp = map;
-		*curr_dsop = dso;
+		dso__put(*curr_dsop);
+		*curr_dsop = dso__get(dso);
 		return 0;
 	}
 
@@ -1484,8 +1484,8 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
 	 */
 	if (kmodule && adjust_kernel_syms && is_exe_text(shdr->sh_flags) &&
 	    shdr->sh_offset <= max_text_sh_offset) {
-		*curr_mapp = map;
-		*curr_dsop = dso;
+		dso__put(*curr_dsop);
+		*curr_dsop = dso__get(dso);
 		return 0;
 	}
 
@@ -1507,10 +1507,10 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
 		dso__set_binary_type(curr_dso, dso__binary_type(dso));
 		dso__set_adjust_symbols(curr_dso, dso__adjust_symbols(dso));
 		curr_map = map__new2(start, curr_dso);
-		dso__put(curr_dso);
-		if (curr_map == NULL)
+		if (curr_map == NULL) {
+			dso__put(curr_dso);
 			return -1;
-
+		}
 		if (dso__kernel(curr_dso))
 			map__kmap(curr_map)->kmaps = kmaps;
 
@@ -1524,21 +1524,15 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
 		dso__set_symtab_type(curr_dso, dso__symtab_type(dso));
 		if (maps__insert(kmaps, curr_map))
 			return -1;
-		/*
-		 * Add it before we drop the reference to curr_map, i.e. while
-		 * we still are sure to have a reference to this DSO via
-		 * *curr_map->dso.
-		 */
 		dsos__add(&maps__machine(kmaps)->dsos, curr_dso);
-		/* kmaps already got it */
-		map__put(curr_map);
 		dso__set_loaded(curr_dso);
-		*curr_mapp = curr_map;
+		dso__put(*curr_dsop);
 		*curr_dsop = curr_dso;
 	} else {
-		*curr_dsop = map__dso(curr_map);
-		map__put(curr_map);
+		dso__put(*curr_dsop);
+		*curr_dsop = dso__get(map__dso(curr_map));
 	}
+	map__put(curr_map);
 
 	return 0;
 }
@@ -1549,11 +1543,9 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 {
 	struct kmap *kmap = dso__kernel(dso) ? map__kmap(map) : NULL;
 	struct maps *kmaps = kmap ? map__kmaps(map) : NULL;
-	struct map *curr_map = map;
-	struct dso *curr_dso = dso;
+	struct dso *curr_dso = NULL;
 	Elf_Data *symstrs, *secstrs, *secstrs_run, *secstrs_sym;
 	uint32_t nr_syms;
-	int err = -1;
 	uint32_t idx;
 	GElf_Ehdr ehdr;
 	GElf_Shdr shdr;
@@ -1656,6 +1648,7 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 	if (kmodule && adjust_kernel_syms)
 		max_text_sh_offset = max_text_section(runtime_ss->elf, &runtime_ss->ehdr);
 
+	curr_dso = dso__get(dso);
 	elf_symtab__for_each_symbol(syms, nr_syms, idx, sym) {
 		struct symbol *f;
 		const char *elf_name = elf_sym__name(&sym, symstrs);
@@ -1744,9 +1737,13 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 			--sym.st_value;
 
 		if (dso__kernel(dso)) {
-			if (dso__process_kernel_symbol(dso, map, &sym, &shdr, kmaps, kmap, &curr_dso, &curr_map,
-						       section_name, adjust_kernel_syms, kmodule,
-						       &remap_kernel, max_text_sh_offset))
+			if (dso__process_kernel_symbol(dso, map, &sym, &shdr,
+						       kmaps, kmap, &curr_dso,
+						       section_name,
+						       adjust_kernel_syms,
+						       kmodule,
+						       &remap_kernel,
+						       max_text_sh_offset))
 				goto out_elf_end;
 		} else if ((used_opd && runtime_ss->adjust_symbols) ||
 			   (!used_opd && syms_ss->adjust_symbols)) {
@@ -1795,6 +1792,7 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 		__symbols__insert(dso__symbols(curr_dso), f, dso__kernel(dso));
 		nr++;
 	}
+	dso__put(curr_dso);
 
 	/*
 	 * For misannotated, zeroed, ASM function sizes.
@@ -1810,9 +1808,10 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 			maps__fixup_end(kmaps);
 		}
 	}
-	err = nr;
+	return nr;
 out_elf_end:
-	return err;
+	dso__put(curr_dso);
+	return -1;
 }
 
 int dso__load_sym(struct dso *dso, struct map *map, struct symsrc *syms_ss,
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog