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Probably fix a segfault in PathLocks

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This commit is contained in:
Eelco Dolstra 2016-12-09 13:26:43 +01:00
parent b30d1e7ada
commit 47f587700d
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GPG key ID: 8170B4726D7198DE
1 changed files with 57 additions and 44 deletions
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101
src/libstore/pathlocks.cc
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@ -1,5 +1,6 @@
#include "pathlocks.hh"
#include "util.hh"
#include "sync.hh"
#include <cerrno>
#include <cstdlib>
@ -72,7 +73,7 @@ bool lockFile(int fd, LockType lockType, bool wait)
close a descriptor, the previous lock will be closed as well. And
there is no way to query whether we already have a lock (F_GETLK
only works on locks held by other processes). */
static StringSet lockedPaths; /* !!! not thread-safe */
static Sync<StringSet> lockedPaths_;
PathLocks::PathLocks()
@ -108,49 +109,60 @@ bool PathLocks::lockPaths(const PathSet & _paths,
debug(format("locking path ‘%1%’") % path);
if (lockedPaths.find(lockPath) != lockedPaths.end())
throw Error("deadlock: trying to re-acquire self-held lock");
AutoCloseFD fd;
while (1) {
/* Open/create the lock file. */
fd = openLockFile(lockPath, true);
/* Acquire an exclusive lock. */
if (!lockFile(fd.get(), ltWrite, false)) {
if (wait) {
if (waitMsg != "") printError(waitMsg);
lockFile(fd.get(), ltWrite, true);
} else {
/* Failed to lock this path; release all other
locks. */
unlock();
return false;
}
}
debug(format("lock acquired on ‘%1%’") % lockPath);
/* Check that the lock file hasn't become stale (i.e.,
hasn't been unlinked). */
struct stat st;
if (fstat(fd.get(), &st) == -1)
throw SysError(format("statting lock file ‘%1%’") % lockPath);
if (st.st_size != 0)
/* This lock file has been unlinked, so we're holding
a lock on a deleted file. This means that other
processes may create and acquire a lock on
`lockPath', and proceed. So we must retry. */
debug(format("open lock file ‘%1%’ has become stale") % lockPath);
else
break;
{
auto lockedPaths(lockedPaths_.lock());
if (lockedPaths->count(lockPath))
throw Error("deadlock: trying to re-acquire self-held lock ‘%s’", lockPath);
lockedPaths->insert(lockPath);
}
try {
AutoCloseFD fd;
while (1) {
/* Open/create the lock file. */
fd = openLockFile(lockPath, true);
/* Acquire an exclusive lock. */
if (!lockFile(fd.get(), ltWrite, false)) {
if (wait) {
if (waitMsg != "") printError(waitMsg);
lockFile(fd.get(), ltWrite, true);
} else {
/* Failed to lock this path; release all other
locks. */
unlock();
return false;
}
}
debug(format("lock acquired on ‘%1%’") % lockPath);
/* Check that the lock file hasn't become stale (i.e.,
hasn't been unlinked). */
struct stat st;
if (fstat(fd.get(), &st) == -1)
throw SysError(format("statting lock file ‘%1%’") % lockPath);
if (st.st_size != 0)
/* This lock file has been unlinked, so we're holding
a lock on a deleted file. This means that other
processes may create and acquire a lock on
`lockPath', and proceed. So we must retry. */
debug(format("open lock file ‘%1%’ has become stale") % lockPath);
else
break;
}
/* Use borrow so that the descriptor isn't closed. */
fds.push_back(FDPair(fd.release(), lockPath));
} catch (...) {
lockedPaths_.lock()->erase(lockPath);
throw;
}
/* Use borrow so that the descriptor isn't closed. */
fds.push_back(FDPair(fd.release(), lockPath));
lockedPaths.insert(lockPath);
}
return true;
@ -172,7 +184,8 @@ void PathLocks::unlock()
for (auto & i : fds) {
if (deletePaths) deleteLockFile(i.second, i.first);
lockedPaths.erase(i.second);
lockedPaths_.lock()->erase(i.second);
if (close(i.first) == -1)
printError(
format("error (ignored): cannot close lock file on ‘%1%’") % i.second);
@ -193,7 +206,7 @@ void PathLocks::setDeletion(bool deletePaths)
bool pathIsLockedByMe(const Path & path)
{
Path lockPath = path + ".lock";
return lockedPaths.find(lockPath) != lockedPaths.end();
return lockedPaths_.lock()->count(lockPath);
}