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Merge "libsnapshot: Fix a race condition in WaitForDelete." am: c6b6c08f95

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Original change: https://android-review.googlesource.com/c/platform/system/core/+/1549339

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I26fa83a768b02728aab002628946d27d7abc77b2
This commit is contained in:
David Anderson 2021-01-13 17:37:24 +00:00 • committed by Automerger Merge Worker
commit bc315cf748
2 changed files with 43 additions and 26 deletions
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49
fs_mgr/libsnapshot/snapuserd_server.cpp
View file

@ -77,9 +77,8 @@ void SnapuserdServer::ShutdownThreads() {
JoinAllThreads();
}
const std::string& DmUserHandler::GetMiscName() const {
return snapuserd_->GetMiscName();
}
DmUserHandler::DmUserHandler(std::unique_ptr<Snapuserd>&& snapuserd)
: snapuserd_(std::move(snapuserd)), misc_name_(snapuserd_->GetMiscName()) {}
bool SnapuserdServer::Sendmsg(android::base::borrowed_fd fd, const std::string& msg) {
ssize_t ret = TEMP_FAILURE_RETRY(send(fd.get(), msg.data(), msg.size(), 0));
@ -148,7 +147,7 @@ bool SnapuserdServer::Receivemsg(android::base::borrowed_fd fd, const std::strin
LOG(ERROR) << "Could not find handler: " << out[1];
return Sendmsg(fd, "fail");
}
if ((*iter)->snapuserd()->IsAttached()) {
if (!(*iter)->snapuserd() || (*iter)->snapuserd()->IsAttached()) {
LOG(ERROR) << "Tried to re-attach control device: " << out[1];
return Sendmsg(fd, "fail");
}
@ -185,7 +184,7 @@ bool SnapuserdServer::Receivemsg(android::base::borrowed_fd fd, const std::strin
LOG(ERROR) << "Malformed delete message, " << out.size() << " parts";
return Sendmsg(fd, "fail");
}
if (!RemoveHandler(out[1], true)) {
if (!RemoveAndJoinHandler(out[1])) {
return Sendmsg(fd, "fail");
}
return Sendmsg(fd, "success");
@ -203,20 +202,38 @@ bool SnapuserdServer::Receivemsg(android::base::borrowed_fd fd, const std::strin
}
void SnapuserdServer::RunThread(std::shared_ptr<DmUserHandler> handler) {
LOG(INFO) << "Entering thread for handler: " << handler->GetMiscName();
LOG(INFO) << "Entering thread for handler: " << handler->misc_name();
while (!StopRequested()) {
if (!handler->snapuserd()->Run()) {
LOG(INFO) << "Snapuserd: Thread terminating";
break;
}
}
LOG(INFO) << "Exiting thread for handler: " << handler->GetMiscName();
auto misc_name = handler->misc_name();
LOG(INFO) << "Handler thread about to exit: " << misc_name;
// If the main thread called RemoveHandler, the handler was already removed
// from within the lock, and calling RemoveHandler again has no effect.
RemoveHandler(handler->GetMiscName(), false);
{
std::lock_guard<std::mutex> lock(lock_);
auto iter = FindHandler(&lock, handler->misc_name());
if (iter == dm_users_.end()) {
// RemoveAndJoinHandler() already removed us from the list, and is
// now waiting on a join(), so just return.
LOG(INFO) << "Exiting handler thread to allow for join: " << misc_name;
return;
}
LOG(INFO) << "Exiting handler thread and freeing resources: " << misc_name;
if (handler->snapuserd()->IsAttached()) {
handler->thread().detach();
}
// Important: free resources within the lock. This ensures that if
// WaitForDelete() is called, the handler is either in the list, or
// it's not and its resources are guaranteed to be freed.
handler->FreeResources();
}
}
bool SnapuserdServer::Start(const std::string& socketname) {
@ -351,7 +368,7 @@ bool SnapuserdServer::StartHandler(const std::shared_ptr<DmUserHandler>& handler
CHECK(!handler->snapuserd()->IsAttached());
if (!handler->snapuserd()->InitBackingAndControlDevice()) {
LOG(ERROR) << "Failed to initialize control device: " << handler->GetMiscName();
LOG(ERROR) << "Failed to initialize control device: " << handler->misc_name();
return false;
}
@ -364,14 +381,14 @@ auto SnapuserdServer::FindHandler(std::lock_guard<std::mutex>* proof_of_lock,
CHECK(proof_of_lock);
for (auto iter = dm_users_.begin(); iter != dm_users_.end(); iter++) {
if ((*iter)->GetMiscName() == misc_name) {
if ((*iter)->misc_name() == misc_name) {
return iter;
}
}
return dm_users_.end();
}
bool SnapuserdServer::RemoveHandler(const std::string& misc_name, bool wait) {
bool SnapuserdServer::RemoveAndJoinHandler(const std::string& misc_name) {
std::shared_ptr<DmUserHandler> handler;
{
std::lock_guard<std::mutex> lock(lock_);
@ -386,10 +403,8 @@ bool SnapuserdServer::RemoveHandler(const std::string& misc_name, bool wait) {
}
auto& th = handler->thread();
if (th.joinable() && wait) {
if (th.joinable()) {
th.join();
} else if (handler->snapuserd()->IsAttached()) {
th.detach();
}
return true;
}

20
fs_mgr/libsnapshot/snapuserd_server.h
View file

@ -46,18 +46,19 @@ enum class DaemonOperations {
};
class DmUserHandler {
private:
std::thread thread_;
std::unique_ptr<Snapuserd> snapuserd_;
public:
explicit DmUserHandler(std::unique_ptr<Snapuserd>&& snapuserd)
: snapuserd_(std::move(snapuserd)) {}
explicit DmUserHandler(std::unique_ptr<Snapuserd>&& snapuserd);
void FreeResources() { snapuserd_ = nullptr; }
const std::unique_ptr<Snapuserd>& snapuserd() const { return snapuserd_; }
std::thread& thread() { return thread_; }
const std::string& GetMiscName() const;
const std::string& misc_name() const { return misc_name_; }
private:
std::thread thread_;
std::unique_ptr<Snapuserd> snapuserd_;
std::string misc_name_;
};
class Stoppable {
@ -71,8 +72,9 @@ class Stoppable {
bool StopRequested() {
// checks if value in future object is available
if (futureObj_.wait_for(std::chrono::milliseconds(0)) == std::future_status::timeout)
if (futureObj_.wait_for(std::chrono::milliseconds(0)) == std::future_status::timeout) {
return false;
}
return true;
}
// Request the thread to stop by setting value in promise object
@ -98,7 +100,7 @@ class SnapuserdServer : public Stoppable {
bool Receivemsg(android::base::borrowed_fd fd, const std::string& str);
void ShutdownThreads();
bool RemoveHandler(const std::string& control_device, bool wait);
bool RemoveAndJoinHandler(const std::string& control_device);
DaemonOperations Resolveop(std::string& input);
std::string GetDaemonStatus();
void Parsemsg(std::string const& msg, const char delim, std::vector<std::string>& out);