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Fix a race around SQLite DB config validation

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The DB config is a single-row table, and the first Podman process
to run against the database creates it. However, there was a race
where multiple Podman processes, started simultaneously, could
try and write it. Only the first would succeed, with subsequent
processes failing once (and then running correctly once re-ran),
but it was happening often in CI and deserves fixing.

[NO NEW TESTS NEEDED] It's a CI flake fix.

Signed-off-by: Matt Heon <mheon@redhat.com>
This commit is contained in:
Matt Heon
2023-03-23 10:48:09 -04:00
committed by Matthew Heon
parent cb18a33f63
commit e061cb968c
1 changed files with 26 additions and 15 deletions
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41
libpod/sqlite_state.go
View File

@ -333,23 +333,30 @@ func (s *SQLiteState) ValidateDBConfig(runtime *Runtime) (defErr error) {
runtimeGraphDriver = storeOpts.GraphDriverName
}
row := s.conn.QueryRow("SELECT Os, StaticDir, TmpDir, GraphRoot, RunRoot, GraphDriver, VolumeDir FROM DBConfig;")
// We have to do this in a transaction to ensure mutual exclusion.
// Otherwise we have a race - multiple processes can be checking the
// row's existence simultaneously, both try to create it, second one to
// get the transaction lock gets an error.
// TODO: The transaction isn't strictly necessary, and there's a (small)
// chance it's a perf hit. If it is, we can move it entirely within the
// `errors.Is()` block below, with extra validation to ensure the row
// still does not exist (and, if it does, to retry this function).
tx, err := s.conn.Begin()
if err != nil {
return fmt.Errorf("beginning database validation transaction: %w", err)
}
defer func() {
if defErr != nil {
if err := tx.Rollback(); err != nil {
logrus.Errorf("Rolling back transaction to validate database: %v", err)
}
}
}()
row := tx.QueryRow("SELECT Os, StaticDir, TmpDir, GraphRoot, RunRoot, GraphDriver, VolumeDir FROM DBConfig;")
if err := row.Scan(&os, &staticDir, &tmpDir, &graphRoot, &runRoot, &graphDriver, &volumePath); err != nil {
if errors.Is(err, sql.ErrNoRows) {
// Need to create runtime config info in DB
tx, err := s.conn.Begin()
if err != nil {
return fmt.Errorf("beginning DB config transaction: %w", err)
}
defer func() {
if defErr != nil {
if err := tx.Rollback(); err != nil {
logrus.Errorf("Rolling back transaction to create DB config: %v", err)
}
}
}()
if _, err := tx.Exec(createRow, 1, schemaVersion, runtimeOS,
runtimeStaticDir, runtimeTmpDir, runtimeGraphRoot,
runtimeRunRoot, runtimeGraphDriver, runtimeVolumePath); err != nil {
@ -357,7 +364,7 @@ func (s *SQLiteState) ValidateDBConfig(runtime *Runtime) (defErr error) {
}
if err := tx.Commit(); err != nil {
return fmt.Errorf("committing DB config transaction: %w", err)
return fmt.Errorf("committing write of database validation row: %w", err)
}
return nil
@ -366,6 +373,10 @@ func (s *SQLiteState) ValidateDBConfig(runtime *Runtime) (defErr error) {
return fmt.Errorf("retrieving DB config: %w", err)
}
if err := tx.Commit(); err != nil {
return fmt.Errorf("committing database validation row: %w", err)
}
checkField := func(fieldName, dbVal, ourVal string) error {
if dbVal != ourVal {
return fmt.Errorf("database %s %q does not match our %s %q: %w", fieldName, dbVal, fieldName, ourVal, define.ErrDBBadConfig)