Bug 154841

Summary: regress/script-tests/double-pollution-putbyoffset.js.ftl-eager timed out because of a lock ordering deadlock involving InferredType and CodeBlock
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Filip Pizlo <fpizlo>
Status: RESOLVED FIXED    
Severity: Normal CC: commit-queue, keith_miller, mark.lam, msaboff, sbarati
Priority: P2    
Version: WebKit Nightly Build   
Hardware: All   
OS: All   
Attachments:
Description Flags
the patch benjamin: review+

Description Filip Pizlo 2016-02-29 16:48:57 PST
Yucky!
Comment 1 Filip Pizlo 2016-02-29 16:56:17 PST
Here's the deadlock:

Main thread:
    1) Change an InferredType.  This acquires InferredType::m_lock.
    2) Fire watchpoint set.  This triggers CodeBlock invalidation, which acquires CodeBlock::m_lock.

DFG thread:
    1) Iterate over the information in a CodeBlock.  This acquires CodeBlock::m_lock.
    2) Ask an InferredType for its descriptor().  This acquires InferredType::m_lock.

I think that the DFG thread's ordering should be legal, because the best logic for lock hierarchies is that locks that protect the largest set of stuff should be acquired first.

This means that the main thread shouldn't be holding the InferredType::m_lock when firing watchpoint sets.  I think that we already do magic for this in other places.
Comment 2 Filip Pizlo 2016-02-29 17:33:46 PST
Created attachment 272533 [details]
the patch
Comment 3 Filip Pizlo 2016-02-29 19:19:18 PST
Landed in http://trac.webkit.org/changeset/197381