#20613 closed Bug (fixed)
LocMem cache may cause deadlocks
| Reported by: | Rafal Stozek | Owned by: | nobody |
|---|---|---|---|
| Component: | Core (Cache system) | Version: | dev |
| Severity: | Normal | Keywords: | |
| Cc: | Triage Stage: | Accepted | |
| Has patch: | yes | Needs documentation: | no |
| Needs tests: | no | Patch needs improvement: | no |
| Easy pickings: | yes | UI/UX: | no |
Description
LocMem cache uses locks to synchronize access to the cache dict.
The problem is that pickle dumps/loads is executed inside code blocks which acquired a reader/writer lock. Pickle dumps/loads can execute parts of user's code to accomplish it's task. The problem starts when user's code tries to retrieve something from the cache.
In that situation for example set() acquires a lock, calls pickle.dumps() which calls user's code, which calls get(), which tries to acquire a lock - causing a deadlock. Very rare situation but it does happen.
Change History (7)
comment:1 Changed 10 years ago by
comment:2 Changed 10 years ago by
I added a pull request for this. Could someone review it? https://github.com/django/django/pull/1296
comment:3 Changed 10 years ago by
| Has patch: | set |
|---|---|
| Patch needs improvement: | set |
| Triage Stage: | Unreviewed → Accepted |
Looked at your pull request and found one issue, I've added a line comment on GitHub. Did you run the (cache) tests?
comment:4 Changed 10 years ago by
I have made the changes that you had suggested. The commit was squashed into the previous pull, not sure if that come out okay. The cache tests does pass.
comment:5 Changed 10 years ago by
| Patch needs improvement: | unset |
|---|---|
| Version: | 1.5 → master |
comment:6 Changed 10 years ago by
| Resolution: | → fixed |
|---|---|
| Status: | new → closed |
The solution would be to move pickle.dumps/loads calls outside of the
with self._lock.reader()/writer()blocks.