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roots: don't share a RootFetcher between threads

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If the send workaround is enabled, it is possible for two threads (a
thread running the crawl_new task, and a thread attempting to apply the
send workaround) to access the same RootFetcher object at the same time.
That never ends well.

Give each function its own BtrfsRootFetcher object.

Fixes: https://github.com/Zygo/bees/issues/250
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2023-02-20 11:13:18 -05:00
parent fd6c3b3769
commit d5a99c2f5e
2 changed files with 4 additions and 4 deletions
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7
src/bees-roots.cc
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@ -500,7 +500,8 @@ BeesRoots::transid_max_nocache()
// We look for the root of the extent tree and read its transid. // We look for the root of the extent tree and read its transid.
// Should run in O(1) time and be fairly reliable. // Should run in O(1) time and be fairly reliable.
const auto bti = m_root_fetcher.root(BTRFS_EXTENT_TREE_OBJECTID); BtrfsRootFetcher root_fetcher(m_ctx->root_fd());
const auto bti = root_fetcher.root(BTRFS_EXTENT_TREE_OBJECTID);
BEESTRACE("extracting transid from " << bti); BEESTRACE("extracting transid from " << bti);
const auto rv = bti.transid(); const auto rv = bti.transid();
@ -927,7 +928,6 @@ BeesRoots::state_load()
BeesRoots::BeesRoots(shared_ptr<BeesContext> ctx) : BeesRoots::BeesRoots(shared_ptr<BeesContext> ctx) :
m_ctx(ctx), m_ctx(ctx),
m_root_fetcher(ctx->root_fd()),
m_crawl_state_file(ctx->home_fd(), crawl_state_filename()), m_crawl_state_file(ctx->home_fd(), crawl_state_filename()),
m_crawl_thread("crawl_transid"), m_crawl_thread("crawl_transid"),
m_writeback_thread("crawl_writeback") m_writeback_thread("crawl_writeback")
@ -1101,7 +1101,8 @@ BeesRoots::is_root_ro(uint64_t root)
BEESTRACE("checking subvol flags on root " << root); BEESTRACE("checking subvol flags on root " << root);
const auto item = m_root_fetcher.root(root); BtrfsRootFetcher root_fetcher(m_ctx->root_fd());
const auto item = root_fetcher.root(root);
// If we can't access the subvol's root item...guess it's ro? // If we can't access the subvol's root item...guess it's ro?
if (!item || item.root_flags() & BTRFS_ROOT_SUBVOL_RDONLY) { if (!item || item.root_flags() & BTRFS_ROOT_SUBVOL_RDONLY) {
return true; return true;

1
src/bees.h
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@ -534,7 +534,6 @@ class BeesScanMode;
class BeesRoots : public enable_shared_from_this<BeesRoots> { class BeesRoots : public enable_shared_from_this<BeesRoots> {
shared_ptr<BeesContext> m_ctx; shared_ptr<BeesContext> m_ctx;
BtrfsRootFetcher m_root_fetcher;
BeesStringFile m_crawl_state_file; BeesStringFile m_crawl_state_file;
map<uint64_t, shared_ptr<BeesCrawl>> m_root_crawl_map; map<uint64_t, shared_ptr<BeesCrawl>> m_root_crawl_map;
mutex m_mutex; mutex m_mutex;