From: Tom Tromey <tom@tromey.com>
To: gdb-patches@sourceware.org
Cc: Tom Tromey <tom@tromey.com>
Subject: [PATCH] Fix race in background index-cache writing
Date: Fri, 24 Mar 2023 15:55:28 -0600 [thread overview]
Message-ID: <20230324215528.891455-1-tom@tromey.com> (raw)
Tom de Vries pointed out a bug in the index-cache background writer --
sometimes it will fail. He also noted that it fails when the number
of worker threads is set to zero. These turn out to be the same
problem -- the cache can't be written to until the per-BFD's
"index_table" member is set.
This patch avoids the race by rearranging the code slightly, to ensure
the cache cannot possibly be written before the member is set.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30261
---
gdb/dwarf2/cooked-index.c | 24 +++++++++++++++---------
gdb/dwarf2/cooked-index.h | 5 ++++-
gdb/dwarf2/read.c | 6 +++++-
3 files changed, 24 insertions(+), 11 deletions(-)
diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index 3a907690906..167beb2bf0e 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -442,26 +442,32 @@ cooked_index_shard::wait (bool allow_quit) const
m_future.wait ();
}
-cooked_index::cooked_index (vec_type &&vec, dwarf2_per_bfd *per_bfd)
+cooked_index::cooked_index (vec_type &&vec)
: m_vector (std::move (vec))
{
for (auto &idx : m_vector)
idx->finalize ();
- /* This must be set after all the finalization tasks have been
- started, because it may call 'wait'. */
- m_write_future
- = gdb::thread_pool::g_thread_pool->post_task ([this, per_bfd] ()
- {
- maybe_write_index (per_bfd);
- });
-
/* ACTIVE_VECTORS is not locked, and this assert ensures that this
will be caught if ever moved to the background. */
gdb_assert (is_main_thread ());
active_vectors.insert (this);
}
+/* See cooked-index.h. */
+
+void
+cooked_index::start_writing_index (dwarf2_per_bfd *per_bfd)
+{
+ /* This must be set after all the finalization tasks have been
+ started, because it may call 'wait'. */
+ m_write_future
+ = gdb::thread_pool::g_thread_pool->post_task ([this, per_bfd] ()
+ {
+ maybe_write_index (per_bfd);
+ });
+}
+
cooked_index::~cooked_index ()
{
/* The 'finalize' method may be run in a different thread. If
diff --git a/gdb/dwarf2/cooked-index.h b/gdb/dwarf2/cooked-index.h
index b16b87bbb0e..f2664929e52 100644
--- a/gdb/dwarf2/cooked-index.h
+++ b/gdb/dwarf2/cooked-index.h
@@ -366,7 +366,7 @@ class cooked_index : public dwarf_scanner_base
object. */
using vec_type = std::vector<std::unique_ptr<cooked_index_shard>>;
- cooked_index (vec_type &&vec, dwarf2_per_bfd *per_bfd);
+ explicit cooked_index (vec_type &&vec);
~cooked_index () override;
DISABLE_COPY_AND_ASSIGN (cooked_index);
@@ -429,6 +429,9 @@ class cooked_index : public dwarf_scanner_base
m_write_future.wait ();
}
+ /* Start writing to the index cache, if the user asked for this. */
+ void start_writing_index (dwarf2_per_bfd *per_bfd);
+
private:
/* Maybe write the index to the index cache. */
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index c910be875a3..dbf323d0da0 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -5147,9 +5147,13 @@ dwarf2_build_psymtabs_hard (dwarf2_per_objfile *per_objfile)
indexes.push_back (index_storage.release ());
indexes.shrink_to_fit ();
- cooked_index *vec = new cooked_index (std::move (indexes), per_bfd);
+ cooked_index *vec = new cooked_index (std::move (indexes));
per_bfd->index_table.reset (vec);
+ /* Cannot start writing the index entry until after the
+ 'index_table' member has been set. */
+ vec->start_writing_index (per_bfd);
+
const cooked_index_entry *main_entry = vec->get_main ();
if (main_entry != nullptr)
{
--
2.39.1
next reply other threads:[~2023-03-24 21:55 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-24 21:55 Tom Tromey [this message]
2023-03-30 14:27 ` Simon Marchi
2023-03-31 14:39 ` Tom Tromey
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