diff --git a/modules/gitrepo/fetch.go b/modules/gitrepo/fetch.go
index 5c86f70cac..0474d6111e 100644
--- a/modules/gitrepo/fetch.go
+++ b/modules/gitrepo/fetch.go
@@ -7,6 +7,7 @@ import (
 	"context"
 
 	"code.gitea.io/gitea/modules/git/gitcmd"
+	"code.gitea.io/gitea/modules/globallock"
 )
 
 // FetchRemoteCommit fetches a specific commit and its related objects from a remote
@@ -19,7 +20,9 @@ import (
 // This behavior is sufficient for temporary operations, such as determining the
 // merge base between commits.
 func FetchRemoteCommit(ctx context.Context, repo, remoteRepo Repository, commitID string) error {
-	return RunCmd(ctx, repo, gitcmd.NewCommand("fetch", "--no-tags").
-		AddDynamicArguments(repoPath(remoteRepo)).
-		AddDynamicArguments(commitID))
+	return globallock.LockAndDo(ctx, getRepoWriteLockKey(repo.RelativePath()), func(ctx context.Context) error {
+		return RunCmd(ctx, repo, gitcmd.NewCommand("fetch", "--no-tags").
+			AddDynamicArguments(repoPath(remoteRepo)).
+			AddDynamicArguments(commitID))
+	})
 }
diff --git a/modules/gitrepo/push.go b/modules/gitrepo/push.go
index 920c317f79..a8945b5392 100644
--- a/modules/gitrepo/push.go
+++ b/modules/gitrepo/push.go
@@ -7,6 +7,7 @@ import (
 	"context"
 
 	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/globallock"
 )
 
 // PushToExternal pushes a managed repository to an external remote.
@@ -16,12 +17,16 @@ func PushToExternal(ctx context.Context, repo Repository, opts git.PushOptions)
 
 // Push pushes from one managed repository to another managed repository.
 func Push(ctx context.Context, fromRepo, toRepo Repository, opts git.PushOptions) error {
-	opts.Remote = repoPath(toRepo)
-	return git.Push(ctx, repoPath(fromRepo), opts)
+	return globallock.LockAndDo(ctx, getRepoWriteLockKey(toRepo.RelativePath()), func(ctx context.Context) error {
+		opts.Remote = repoPath(toRepo)
+		return git.Push(ctx, repoPath(fromRepo), opts)
+	})
 }
 
 // PushFromLocal pushes from a local path to a managed repository.
 func PushFromLocal(ctx context.Context, fromLocalPath string, toRepo Repository, opts git.PushOptions) error {
-	opts.Remote = repoPath(toRepo)
-	return git.Push(ctx, fromLocalPath, opts)
+	return globallock.LockAndDo(ctx, getRepoWriteLockKey(toRepo.RelativePath()), func(ctx context.Context) error {
+		opts.Remote = repoPath(toRepo)
+		return git.Push(ctx, fromLocalPath, opts)
+	})
 }
diff --git a/modules/gitrepo/repo_lock.go b/modules/gitrepo/repo_lock.go
new file mode 100644
index 0000000000..2eb89ce807
--- /dev/null
+++ b/modules/gitrepo/repo_lock.go
@@ -0,0 +1,10 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package gitrepo
+
+// getRepoWriteLockKey returns the global lock key for write operations on the repository.
+// Parallel write operations on the same git repository should be avoided to prevent data corruption.
+func getRepoWriteLockKey(repoStoragePath string) string {
+	return "repo-write:" + repoStoragePath
+}
diff --git a/services/git/compare.go b/services/git/compare.go
index 48c60688e3..9e4645c5b1 100644
--- a/services/git/compare.go
+++ b/services/git/compare.go
@@ -65,8 +65,11 @@ func GetCompareInfo(ctx context.Context, baseRepo, headRepo *repo_model.Reposito
 	// if they are not the same repository, then we need to fetch the base commit into the head repository
 	// because we will use headGitRepo in the following code
 	if baseRepo.ID != headRepo.ID {
-		if err := gitrepo.FetchRemoteCommit(ctx, headRepo, baseRepo, compareInfo.BaseCommitID); err != nil {
-			return nil, fmt.Errorf("FetchRemoteCommit: %w", err)
+		exist := headGitRepo.IsCommitExist(compareInfo.BaseCommitID)
+		if !exist {
+			if err := gitrepo.FetchRemoteCommit(ctx, headRepo, baseRepo, compareInfo.BaseCommitID); err != nil {
+				return nil, fmt.Errorf("FetchRemoteCommit: %w", err)
+			}
 		}
 	}