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UserLock: Fix multi-threaded access to a global variable

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This commit is contained in:
Eelco Dolstra 2017-01-25 13:00:38 +01:00
parent a55f589720
commit 951357e5fb
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GPG key ID: 8170B4726D7198DE
1 changed files with 39 additions and 29 deletions
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22
src/libstore/build.cc
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@ -434,7 +434,7 @@ private:
close that file again (without closing the original file close that file again (without closing the original file
descriptor), we lose the lock. So we have to be *very* careful descriptor), we lose the lock. So we have to be *very* careful
not to open a lock file on which we are holding a lock. */ not to open a lock file on which we are holding a lock. */
static PathSet lockedPaths; /* !!! not thread-safe */ static Sync<PathSet> lockedPaths_;
Path fnUserLock; Path fnUserLock;
AutoCloseFD fdUserLock; AutoCloseFD fdUserLock;
@ -460,7 +460,7 @@ public:
}; };
PathSet UserLock::lockedPaths; Sync<PathSet> UserLock::lockedPaths_;
UserLock::UserLock() UserLock::UserLock()
@ -499,9 +499,15 @@ UserLock::UserLock()
fnUserLock = (format("%1%/userpool/%2%") % settings.nixStateDir % pw->pw_uid).str(); fnUserLock = (format("%1%/userpool/%2%") % settings.nixStateDir % pw->pw_uid).str();
if (lockedPaths.find(fnUserLock) != lockedPaths.end()) {
auto lockedPaths(lockedPaths_.lock());
if (lockedPaths->count(fnUserLock))
/* We already have a lock on this one. */ /* We already have a lock on this one. */
continue; continue;
lockedPaths->insert(fnUserLock);
}
try {
AutoCloseFD fd = open(fnUserLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600); AutoCloseFD fd = open(fnUserLock.c_str(), O_RDWR | O_CREAT | O_CLOEXEC, 0600);
if (!fd) if (!fd)
@ -509,7 +515,6 @@ UserLock::UserLock()
if (lockFile(fd.get(), ltWrite, false)) { if (lockFile(fd.get(), ltWrite, false)) {
fdUserLock = std::move(fd); fdUserLock = std::move(fd);
lockedPaths.insert(fnUserLock);
user = i; user = i;
uid = pw->pw_uid; uid = pw->pw_uid;
@ -533,6 +538,10 @@ UserLock::UserLock()
return; return;
} }
} catch (...) {
lockedPaths_.lock()->erase(fnUserLock);
}
} }
throw Error(format("all build users are currently in use; " throw Error(format("all build users are currently in use; "
@ -543,8 +552,9 @@ UserLock::UserLock()
UserLock::~UserLock() UserLock::~UserLock()
{ {
assert(lockedPaths.count(fnUserLock)); auto lockedPaths(lockedPaths_.lock());
lockedPaths.erase(fnUserLock); assert(lockedPaths->count(fnUserLock));
lockedPaths->erase(fnUserLock);
} }