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Release shared lock before acquiring exclusive lock

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In principle, this should avoid deadlocks where two instances of Nix are
holding a shared lock on big-lock and are both waiting to get an
exclusive lock.

However, it seems like `flock(2)` is supposed to do this automatically,
so it's not clear whether this is actually where the problem comes from.
This commit is contained in:
Naïm Favier 2022-12-17 18:31:00 +01:00
parent 26c7602c39
commit 81c3f99b36
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GPG key ID: 95AFCE8211908325
1 changed files with 2 additions and 0 deletions
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2
src/libstore/local-store.cc
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@ -91,6 +91,7 @@ void migrateCASchema(SQLite& db, Path schemaPath, AutoCloseFD& lockFd)
if (!lockFile(lockFd.get(), ltWrite, false)) { if (!lockFile(lockFd.get(), ltWrite, false)) {
printInfo("waiting for exclusive access to the Nix store for ca drvs..."); printInfo("waiting for exclusive access to the Nix store for ca drvs...");
lockFile(lockFd.get(), ltNone, false); // We have acquired a shared lock; release it to prevent deadlocks
lockFile(lockFd.get(), ltWrite, true); lockFile(lockFd.get(), ltWrite, true);
} }
@ -299,6 +300,7 @@ LocalStore::LocalStore(const Params & params)
if (!lockFile(globalLock.get(), ltWrite, false)) { if (!lockFile(globalLock.get(), ltWrite, false)) {
printInfo("waiting for exclusive access to the Nix store..."); printInfo("waiting for exclusive access to the Nix store...");
lockFile(globalLock.get(), ltNone, false); // We have acquired a shared lock; release it to prevent deadlocks
lockFile(globalLock.get(), ltWrite, true); lockFile(globalLock.get(), ltWrite, true);
} }