[bugfix] concurrent map writes in dereferencer media processing maps (#2964)

* removes the avatar / header deref maps as we now have per-uri status / account locks, adds retries on data-races, adds separate emoji map mutex

* work with a copy of account / status for each retry loop

* revert to old data race behaviour, it gets too complicated otherwise

---------

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

internal/federation/dereferencing/account.go

@@ -496,7 +496,7 @@ func (d *Dereferencer) enrichAccount(
 				account.Username, account.Domain, err,
 			)
 
-		case err == nil && account.Domain != accDomain:
+		case account.Domain != accDomain:
 			// After webfinger, we now have correct account domain from which we can do a final DB check.
 			alreadyAcc, err := d.state.DB.GetAccountByUsernameDomain(ctx, account.Username, accDomain)
 			if err != nil && !errors.Is(err, db.ErrNoEntries) {
@@ -518,7 +518,7 @@ func (d *Dereferencer) enrichAccount(
 			// or the stub account we were passed.
 			fallthrough
 
-		case err == nil:
+		default:
 			// Update account with latest info.
 			account.URI = accURI.String()
 			account.Domain = accDomain
@@ -531,19 +531,14 @@ func (d *Dereferencer) enrichAccount(
 		// must parse from account.
 		uri, err = url.Parse(account.URI)
 		if err != nil {
-			return nil, nil, gtserror.Newf(
-				"invalid uri %q: %w",
-				account.URI, gtserror.SetUnretrievable(err),
-			)
+			err := gtserror.Newf("invalid uri %q: %w", account.URI, err)
+			return nil, nil, gtserror.SetUnretrievable(err)
 		}
 
 		// Check URI scheme ahead of time for more useful errs.
 		if uri.Scheme != "http" && uri.Scheme != "https" {
-			err := errors.New("account URI scheme must be http or https")
-			return nil, nil, gtserror.Newf(
-				"invalid uri %q: %w",
-				account.URI, gtserror.SetUnretrievable(err),
-			)
+			err := gtserror.Newf("invalid uri %q: scheme must be http(s)", account.URI)
+			return nil, nil, gtserror.SetUnretrievable(err)
 		}
 	}
 
@@ -634,7 +629,7 @@ func (d *Dereferencer) enrichAccount(
 	if err != nil {
 		// ASRepresentationToAccount will set Malformed on the
 		// returned error, so we don't need to do it here.
-		err = gtserror.Newf("error converting accountable to gts model for account %s: %w", uri, err)
+		err = gtserror.Newf("error converting %s to gts model: %w", uri, err)
 		return nil, nil, err
 	}
 
@@ -798,39 +793,16 @@ func (d *Dereferencer) fetchRemoteAccountAvatar(ctx context.Context, tsport tran
 		return gtserror.Newf("error parsing url %s: %w", latestAcc.AvatarRemoteURL, err)
 	}
 
-	// Acquire lock for derefs map.
-	unlock := d.state.FedLocks.Lock(latestAcc.AvatarRemoteURL)
-	unlock = util.DoOnce(unlock)
-	defer unlock()
-
-	// Look for an existing dereference in progress.
-	processing, ok := d.derefAvatars[latestAcc.AvatarRemoteURL]
-
-	if !ok {
-		// Set the media data function to dereference avatar from URI.
-		data := func(ctx context.Context) (io.ReadCloser, int64, error) {
-			return tsport.DereferenceMedia(ctx, avatarURI)
-		}
-
-		// Create new media processing request from the media manager instance.
-		processing = d.mediaManager.PreProcessMedia(data, latestAcc.ID, &media.AdditionalMediaInfo{
-			Avatar:    func() *bool { v := true; return &v }(),
-			RemoteURL: &latestAcc.AvatarRemoteURL,
-		})
-
-		// Store media in map to mark as processing.
-		d.derefAvatars[latestAcc.AvatarRemoteURL] = processing
-
-		defer func() {
-			// On exit safely remove media from map.
-			unlock := d.state.FedLocks.Lock(latestAcc.AvatarRemoteURL)
-			delete(d.derefAvatars, latestAcc.AvatarRemoteURL)
-			unlock()
-		}()
+	// Set the media data function to dereference avatar from URI.
+	data := func(ctx context.Context) (io.ReadCloser, int64, error) {
+		return tsport.DereferenceMedia(ctx, avatarURI)
 	}
 
-	// Unlock map.
-	unlock()
+	// Create new media processing request from the media manager instance.
+	processing := d.mediaManager.PreProcessMedia(data, latestAcc.ID, &media.AdditionalMediaInfo{
+		Avatar:    func() *bool { v := true; return &v }(),
+		RemoteURL: &latestAcc.AvatarRemoteURL,
+	})
 
 	// Start media attachment loading (blocking call).
 	if _, err := processing.LoadAttachment(ctx); err != nil {
@@ -884,39 +856,16 @@ func (d *Dereferencer) fetchRemoteAccountHeader(ctx context.Context, tsport tran
 		return gtserror.Newf("error parsing url %s: %w", latestAcc.HeaderRemoteURL, err)
 	}
 
-	// Acquire lock for derefs map.
-	unlock := d.state.FedLocks.Lock(latestAcc.HeaderRemoteURL)
-	unlock = util.DoOnce(unlock)
-	defer unlock()
-
-	// Look for an existing dereference in progress.
-	processing, ok := d.derefHeaders[latestAcc.HeaderRemoteURL]
-
-	if !ok {
-		// Set the media data function to dereference avatar from URI.
-		data := func(ctx context.Context) (io.ReadCloser, int64, error) {
-			return tsport.DereferenceMedia(ctx, headerURI)
-		}
-
-		// Create new media processing request from the media manager instance.
-		processing = d.mediaManager.PreProcessMedia(data, latestAcc.ID, &media.AdditionalMediaInfo{
-			Header:    func() *bool { v := true; return &v }(),
-			RemoteURL: &latestAcc.HeaderRemoteURL,
-		})
-
-		// Store media in map to mark as processing.
-		d.derefHeaders[latestAcc.HeaderRemoteURL] = processing
-
-		defer func() {
-			// On exit safely remove media from map.
-			unlock := d.state.FedLocks.Lock(latestAcc.HeaderRemoteURL)
-			delete(d.derefHeaders, latestAcc.HeaderRemoteURL)
-			unlock()
-		}()
+	// Set the media data function to dereference avatar from URI.
+	data := func(ctx context.Context) (io.ReadCloser, int64, error) {
+		return tsport.DereferenceMedia(ctx, headerURI)
 	}
 
-	// Unlock map.
-	unlock()
+	// Create new media processing request from the media manager instance.
+	processing := d.mediaManager.PreProcessMedia(data, latestAcc.ID, &media.AdditionalMediaInfo{
+		Header:    func() *bool { v := true; return &v }(),
+		RemoteURL: &latestAcc.HeaderRemoteURL,
+	})
 
 	// Start media attachment loading (blocking call).
 	if _, err := processing.LoadAttachment(ctx); err != nil {

internal/federation/dereferencing/dereferencer.go

@@ -85,11 +85,22 @@ type Dereferencer struct {
 	mediaManager        *media.Manager
 	visibility          *visibility.Filter
 
-	// all protected by State{}.FedLocks.
-	derefAvatars map[string]*media.ProcessingMedia
-	derefHeaders map[string]*media.ProcessingMedia
-	derefEmojis  map[string]*media.ProcessingEmoji
+	// in-progress dereferencing emoji. we already perform
+	// locks per-status and per-account so we don't need
+	// processing maps for other media which won't often
+	// end up being repeated. worst case we run into an
+	// db.ErrAlreadyExists error which then gets handled
+	// appropriately by enrich{Account,Status}Safely().
+	derefEmojis   map[string]*media.ProcessingEmoji
+	derefEmojisMu sync.Mutex
 
+	// handshakes marks current in-progress handshakes
+	// occurring, useful to prevent a deadlock between
+	// gotosocial instances attempting to dereference
+	// accounts for the first time. when a handshake is
+	// currently ongoing we know not to block waiting
+	// on certain data and instead return an in-progress
+	// form of the data as we currently see it.
 	handshakes   map[string][]*url.URL
 	handshakesMu sync.Mutex
 }
@@ -108,8 +119,6 @@ func NewDereferencer(
 		transportController: transportController,
 		mediaManager:        mediaManager,
 		visibility:          visFilter,
-		derefAvatars:        make(map[string]*media.ProcessingMedia),
-		derefHeaders:        make(map[string]*media.ProcessingMedia),
 		derefEmojis:         make(map[string]*media.ProcessingEmoji),
 		handshakes:          make(map[string][]*url.URL),
 	}

internal/federation/dereferencing/emoji.go

@@ -24,6 +24,7 @@
 	"net/url"
 
 	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/id"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
@@ -31,11 +32,8 @@
 	"github.com/superseriousbusiness/gotosocial/internal/util"
 )
 
-func (d *Dereferencer) GetRemoteEmoji(ctx context.Context, requestingUsername string, remoteURL string, shortcode string, domain string, id string, emojiURI string, ai *media.AdditionalEmojiInfo, refresh bool) (*media.ProcessingEmoji, error) {
-	var (
-		shortcodeDomain = shortcode + "@" + domain
-		processingEmoji *media.ProcessingEmoji
-	)
+func (d *Dereferencer) GetRemoteEmoji(ctx context.Context, requestUser string, remoteURL string, shortcode string, domain string, id string, emojiURI string, ai *media.AdditionalEmojiInfo, refresh bool) (*media.ProcessingEmoji, error) {
+	var shortcodeDomain = shortcode + "@" + domain
 
 	// Ensure we have been passed a valid URL.
 	derefURI, err := url.Parse(remoteURL)
@@ -43,52 +41,61 @@ func (d *Dereferencer) GetRemoteEmoji(ctx context.Context, requestingUsername st
 		return nil, fmt.Errorf("GetRemoteEmoji: error parsing url for emoji %s: %s", shortcodeDomain, err)
 	}
 
-	// Acquire lock for derefs map.
-	unlock := d.state.FedLocks.Lock(remoteURL)
+	// Acquire derefs lock.
+	d.derefEmojisMu.Lock()
+
+	// Ensure unlock only done once.
+	unlock := d.derefEmojisMu.Unlock
 	unlock = util.DoOnce(unlock)
 	defer unlock()
 
-	// first check if we're already processing this emoji
-	if alreadyProcessing, ok := d.derefEmojis[shortcodeDomain]; ok {
-		// we're already on it, no worries
-		processingEmoji = alreadyProcessing
-	} else {
-		// not processing it yet, let's start
-		t, err := d.transportController.NewTransportForUsername(ctx, requestingUsername)
+	// Look for an existing dereference in progress.
+	processing, ok := d.derefEmojis[shortcodeDomain]
+
+	if !ok {
+		// Fetch a transport for current request user in order to perform request.
+		tsport, err := d.transportController.NewTransportForUsername(ctx, requestUser)
 		if err != nil {
-			return nil, fmt.Errorf("GetRemoteEmoji: error creating transport to fetch emoji %s: %s", shortcodeDomain, err)
+			return nil, gtserror.Newf("couldn't create transport: %w", err)
 		}
 
-		dataFunc := func(innerCtx context.Context) (io.ReadCloser, int64, error) {
-			return t.DereferenceMedia(innerCtx, derefURI)
+		// Set the media data function to dereference emoji from URI.
+		data := func(ctx context.Context) (io.ReadCloser, int64, error) {
+			return tsport.DereferenceMedia(ctx, derefURI)
 		}
 
-		newProcessing, err := d.mediaManager.PreProcessEmoji(ctx, dataFunc, shortcode, id, emojiURI, ai, refresh)
+		// Create new emoji processing request from the media manager.
+		processing, err = d.mediaManager.PreProcessEmoji(ctx, data,
+			shortcode,
+			id,
+			emojiURI,
+			ai,
+			refresh,
+		)
 		if err != nil {
-			return nil, fmt.Errorf("GetRemoteEmoji: error processing emoji %s: %s", shortcodeDomain, err)
+			return nil, gtserror.Newf("error preprocessing emoji %s: %s", shortcodeDomain, err)
 		}
 
-		// store it in our map to indicate it's in process
-		d.derefEmojis[shortcodeDomain] = newProcessing
-		processingEmoji = newProcessing
+		// Store media in map to mark as processing.
+		d.derefEmojis[shortcodeDomain] = processing
+
+		defer func() {
+			// On exit safely remove emoji from map.
+			d.derefEmojisMu.Lock()
+			delete(d.derefEmojis, shortcodeDomain)
+			d.derefEmojisMu.Unlock()
+		}()
 	}
 
 	// Unlock map.
 	unlock()
 
-	defer func() {
-		// On exit safely remove emoji from map.
-		unlock := d.state.FedLocks.Lock(remoteURL)
-		delete(d.derefEmojis, shortcodeDomain)
-		unlock()
-	}()
-
 	// Start emoji attachment loading (blocking call).
-	if _, err := processingEmoji.LoadEmoji(ctx); err != nil {
+	if _, err := processing.LoadEmoji(ctx); err != nil {
 		return nil, err
 	}
 
-	return processingEmoji, nil
+	return processing, nil
 }
 
 func (d *Dereferencer) populateEmojis(ctx context.Context, rawEmojis []*gtsmodel.Emoji, requestingUsername string) ([]*gtsmodel.Emoji, error) {

internal/federation/dereferencing/status.go

@@ -285,7 +285,7 @@ func (d *Dereferencer) enrichStatusSafely(
 	requestUser string,
 	uri *url.URL,
 	status *gtsmodel.Status,
-	apubStatus ap.Statusable,
+	statusable ap.Statusable,
 ) (*gtsmodel.Status, ap.Statusable, bool, error) {
 	uriStr := status.URI
 
@@ -313,7 +313,7 @@ func (d *Dereferencer) enrichStatusSafely(
 		requestUser,
 		uri,
 		status,
-		apubStatus,
+		statusable,
 	)
 
 	if gtserror.StatusCode(err) >= 400 {