From: Tom de Vries <tdevries@suse.de>
To: Tom Tromey <tom@tromey.com>
Cc: gdb-patches@sourceware.org
Subject: Re: [PATCH 5/5] [gdb/symtab] Fix data race on per_cu->lang
Date: Tue, 5 Jul 2022 10:17:05 +0200 [thread overview]
Message-ID: <7d4271d4-5b01-3ddf-fc39-8a4f7e40d9ab@suse.de> (raw)
In-Reply-To: <877d4svih2.fsf@tromey.com>
On 7/4/22 20:30, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
>
> Tom> Both writes are called from the parallel for in dwarf2_build_psymtabs_hard,
> Tom> this one directly:
> Tom> ...
> Tom> #1 process_psymtab_comp_unit gdb/dwarf2/read.c:6812 (gdb+0x830912)
> Tom> #2 operator() gdb/dwarf2/read.c:7102 (gdb+0x831902)
> Tom> #3 operator() gdb/../gdbsupport/parallel-for.h:171 (gdb+0x8723a8)
> Tom> ...
> Tom> and this one when handling cross-CU refs:
> Tom> ...
> Tom> #1 cooked_indexer::ensure_cu_exists(cutu_reader*, dwarf2_per_objfile*, \
> Tom> sect_offset, bool, bool) gdb/dwarf2/read.c:17973 (gdb+0x85c522)
>
> This method tries to ensure that a CU isn't processed twice, using the
> 'scanned' field. Do you know why this isn't working?
>
Yes, because for_scanning == false, so this:
...
/* When scanning, we only want to visit a given CU a single time.
Doing this check here avoids self-imports as well. */
if (for_scanning)
{
bool nope = false;
if (!per_cu->scanned.compare_exchange_strong (nope, true))
return nullptr;
}
...
is not actived.
A quick experiment of setting it to true at the call site:
...
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 23fe5679cbd..f85263564cb 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -18143,7 +18143,7 @@ cooked_indexer::scan_attributes
(dwarf2_per_cu_data *scanning_
per_cu,
{
cutu_reader *new_reader
= ensure_cu_exists (reader, reader->cu->per_objfile, origin_offset,
- origin_is_dwz, false);
+ origin_is_dwz, true);
if (new_reader != nullptr)
{
const gdb_byte *new_info_ptr = (new_reader->buffer
...
makes thread sanitizer stop complaining, but also makes the test-case fail:
...
FAIL: gdb.dwarf2/inlined_subroutine-inheritance.exp: gdb_breakpoint: set
breakpoint at bytes_repeat
...
Thanks,
- Tom
> Tom> Fix this by guarding the write with a lock.
>
> I would rather we avoid locks. Ideally the existing exclusion mechanism
> should be made to work, but if that fails, perhaps we can use another
> atomic.
>
> Tom
next prev parent reply other threads:[~2022-07-05 8:17 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-29 15:29 [PATCH 1/5] [COVER-LETTER, RFC] Fix some fsanitize=thread issues in gdb's cooked index Tom de Vries
2022-06-29 15:29 ` [PATCH 2/5] [gdb/symtab] Fix data race on per_cu->dwarf_version Tom de Vries
2022-07-01 11:16 ` Tom de Vries
2022-07-02 11:07 ` Tom de Vries
2022-07-04 18:51 ` Tom Tromey
2022-07-04 19:43 ` Tom de Vries
2022-07-04 19:53 ` Tom Tromey
2022-06-29 15:29 ` [PATCH 3/5] [gdb/symtab] Work around fsanitize=address false positive for per_cu->lang Tom de Vries
2022-06-29 17:38 ` Pedro Alves
2022-06-29 18:25 ` Pedro Alves
2022-06-29 18:28 ` Pedro Alves
2022-07-04 7:04 ` [PATCH 3/5] [gdb/symtab] Work around fsanitize=address false positive for per_ cu->lang Tom de Vries
2022-07-04 18:32 ` [PATCH 3/5] [gdb/symtab] Work around fsanitize=address false positive for per_cu->lang Tom Tromey
2022-07-04 19:45 ` Tom de Vries
2022-07-06 19:20 ` [PATCH] Introduce struct packed template, fix -fsanitize=thread for per_cu fields Pedro Alves
2022-07-07 10:18 ` Tom de Vries
2022-07-07 15:26 ` Pedro Alves
2022-07-08 14:54 ` Tom de Vries
2022-07-12 10:22 ` Tom de Vries
2022-06-29 15:29 ` [PATCH 4/5] [gdb/symtab] Work around fsanitize=address false positive for per_cu->unit_type Tom de Vries
2022-06-29 15:29 ` [PATCH 5/5] [gdb/symtab] Fix data race on per_cu->lang Tom de Vries
2022-07-04 18:30 ` Tom Tromey
2022-07-05 8:17 ` Tom de Vries [this message]
2022-07-05 15:19 ` Tom de Vries
2022-07-06 15:42 ` Tom de Vries
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