[Bug symtab/30837] New: [gdb/symtab, index-cache] data race on current_inferior_

[Bug symtab/30837] New: [gdb/symtab, index-cache] data race on current_inferior_

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

            Bug ID: 30837
           Summary: [gdb/symtab, index-cache] data race on
                    current_inferior_
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Created attachment 15106
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15106&action=edit
gdb.log

When building gdb with -fsanitize=threads and using soon to be submitted target
board cc-with-index-cache, I run into a data race in test-case
gdb.ada/non-ascii-utf-8.exp
...
==================^M
^[[1m^[[31mWARNING: ThreadSanitizer: data race (pid=25220)^M
^[[1m^[[0m^[[1m^[[34m  Read of size 8 at 0x000003342928 by thread T12:^M
^[[1m^[[0m    #0 gdb::ref_ptr<inferior, refcounted_object_ref_policy>::get()
const /data/vries/gdb/src/gdb/../gdbsupport/gdb_ref_ptr.h:132 (gdb+0xa690b8)^M
    #1 current_inferior() /data/vries/gdb/src/gdb/inferior.c:57
(gdb+0xa63b74)^M
    #2 target_supports_terminal_ours() /data/vries/gdb/src/gdb/target.c:1121
(gdb+0xfaefd4)^M
    #3 vwarning(char const*, __va_list_tag*)
/data/vries/gdb/src/gdb/utils.c:147 (gdb+0x10e54c5)^M
    #4 warning(char const*, ...) /data/vries/gdb/src/gdbsupport/errors.cc:34
(gdb+0x1dc04e4)^M
    #5 ada_encode_1 /data/vries/gdb/src/gdb/ada-lang.c:1000 (gdb+0x47d348)^M
    #6 ada_encode[abi:cxx11](char const*, bool)
/data/vries/gdb/src/gdb/ada-lang.c:1159 (gdb+0x47dd12)^M
    #7 write_cooked_index /data/vries/gdb/src/gdb/dwarf2/index-write.c:1142
(gdb+0x832e42)^M
    #8 write_gdbindex /data/vries/gdb/src/gdb/dwarf2/index-write.c:1236
(gdb+0x83348b)^M
  ...
^M
^[[1m^[[34m  Previous write of size 8 at 0x000003342928 by main thread:^M
^[[1m^[[0m    #0 gdb::ref_ptr<inferior,
refcounted_object_ref_policy>::reset(inferior*)
/data/vries/gdb/src/gdb/../gdbsupport/gdb_ref_ptr.h:125 (gdb+0xa6a2bf)^M
    #1 gdb::ref_ptr<inferior,
refcounted_object_ref_policy>::operator=(gdb::ref_ptr<inferior,
refcounted_object_ref_policy>&&)
/data/vries/gdb/src/gdb/../gdbsupport/gdb_ref_ptr.h:113 (gdb+0xa691cc)^M
    #2 set_current_inferior(inferior*) /data/vries/gdb/src/gdb/inferior.c:66
(gdb+0xa63bf6)^M
    #3 switch_to_inferior_no_thread(inferior*)
/data/vries/gdb/src/gdb/inferior.c:714 (gdb+0xa66df9)^M
    #4 scoped_restore_current_thread::restore()
/data/vries/gdb/src/gdb/thread.c:1397 (gdb+0xfe1f9b)^M
    #5 scoped_restore_current_thread::~scoped_restore_current_thread()
/data/vries/gdb/src/gdb/thread.c:1415 (gdb+0xfe20c9)^M
    #6
scoped_restore_current_pspace_and_thread::~scoped_restore_current_pspace_and_thread()
/data/vries/gdb/src/gdb/progspace-and-thread.h:29 (gdb+0x628ef7)^M
    #7 bp_loc_is_permanent /data/vries/gdb/src/gdb/breakpoint.c:8532
(gdb+0x609bed)^M
    #8 code_breakpoint::add_location(symtab_and_line const&)
/data/vries/gdb/src/gdb/breakpoint.c:8509 (gdb+0x609acc)^M
    #9 internal_breakpoint::internal_breakpoint(gdbarch*, bptype, unsigned
long) /data/vries/gdb/src/gdb/breakpoint.c:350 (gdb+0x6282a3)^M
    #10 create_internal_breakpoint /data/vries/gdb/src/gdb/breakpoint.c:3454
(gdb+0x5f71c0)^M
    #11 create_internal_breakpoint /data/vries/gdb/src/gdb/breakpoint.c:3485
(gdb+0x5f7346)^M
    #12 create_exception_master_breakpoint_hook
/data/vries/gdb/src/gdb/breakpoint.c:3856 (gdb+0x5f86dc)^M
    #13 create_exception_master_breakpoint
/data/vries/gdb/src/gdb/breakpoint.c:3882 (gdb+0x5f8899)^M
    #14 breakpoint_re_set() /data/vries/gdb/src/gdb/breakpoint.c:13262
(gdb+0x61c3f1)^M
    #15 symbol_file_command(char const*, int)
/data/vries/gdb/src/gdb/symfile.c:1686 (gdb+0xf44c8d)^M
    #16 file_command /data/vries/gdb/src/gdb/exec.c:554 (gdb+0x94f99f)^M
...

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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #1 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=f1b8ee6f2b4381bc46a0ad4c233b6eddc1e135b5

commit f1b8ee6f2b4381bc46a0ad4c233b6eddc1e135b5
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Nov 27 21:15:26 2023 +0100

    [gdb/testsuite] Add boards/cc-with-index-cache.exp

    We have a target board cc-with-gdb-index that uses the gdb-add-index script
to
    add a .gdb_index index to an exec.

    There is however an alternative way of adding a .gdb_index: the
index-cache.

    Add a new target board cc-with-index-cache.

    This is not superfluous for two reasons:
    - there is functionality that gdb-add-index doesn't support, but the
      index-cache does: the index-cache can add an index to an exec with a
      .gnu_debugaltlink (note that when using the cc-with-gdb-index board this
      case is quietly ignored), and
    - using the index-cache is excercised in only a few test-cases, and having
      this target board extends the test coverage to the entire test suite. 
This
      is for instance relevant because the index-cache is written by a worker
      thread in the background, so we can check more thoroughly for data races
      (see PR symtab/30837).

    Tested on x86_64-linux.

    Shell script changes checked with shellcheck.

    Approved-By: Tom Tromey <tom@tromey.com>

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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org
           Assignee|unassigned at sourceware dot org   |tromey at sourceware dot org

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
Probably need to defer warnings in this code.

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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |29366


Referenced Bugs:

https://sourceware.org/bugzilla/show_bug.cgi?id=29366
[Bug 29366] [meta] New DWARF indexer meta bug
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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
Also worth noting that if/when the .debug_names writer is fixed,
this warning will be impossible, because that will just be
writing out the DW_AT_name values verbatim.

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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #4 from Tom Tromey <tromey at sourceware dot org> ---
Actually the debug-names writer shouldn't be invoked from the
background so this must be something else.

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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #5 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Tom Tromey from comment #4)
> Actually the debug-names writer shouldn't be invoked from the
> background so this must be something else.

It's the call to ada_encode in index-write.c:write_cooked_index.

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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |15.1

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https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #6 from Tom Tromey <tromey at sourceware dot org> ---
I have a patch for this that I'll send tomorrow.

It's tempting to unify the ways to intercept warnings
and not have a separate "deferred warning" class, but
in the end I chose not to do this for now.

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[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #7 from Tom Tromey <tromey at sourceware dot org> ---
https://sourceware.org/pipermail/gdb-patches/2024-February/206595.html

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[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #8 from Tom Tromey <tromey at sourceware dot org> ---
v2 (just a rebase):
https://sourceware.org/pipermail/gdb-patches/2024-March/207215.html

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[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

--- Comment #9 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom Tromey <tromey@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=818ef5f4137aaff3afdb52f8bbd3a4c3a9ffa28b

commit 818ef5f4137aaff3afdb52f8bbd3a4c3a9ffa28b
Author: Tom Tromey <tromey@adacore.com>
Date:   Tue Feb 13 13:55:34 2024 -0700

    Capture warnings when writing to the index cache

    PR symtab/30837 points out a race that can occur when writing to the
    index cache: a call to ada_encode can cause a warning, which is
    forbidden on a worker thread.

    This patch fixes the problem by arranging to capture any such
    warnings.

    This is v2 of the patch.  It is rebased on top of some other changes
    in the same area.  v1 was here:

        https://sourceware.org/pipermail/gdb-patches/2024-February/206595.html

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30837

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[Bug symtab/30837] [gdb/symtab, index-cache] data race on current_inferior_

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=30837

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #10 from Tom Tromey <tromey at sourceware dot org> ---
Fixed.

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https://sourceware.org/bugzilla/show_bug.cgi?id=30837

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |31751


Referenced Bugs:

https://sourceware.org/bugzilla/show_bug.cgi?id=31751
[Bug 31751] re-enable background DWARF reading
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