Date: Thu, 14 Feb 2019 19:20:02 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: Draft outline of thread-list design On Tue, Feb 12, 2019 at 01:26:25PM -0500, Rich Felker wrote: > Here's a draft of the thread-list design, proposed previously as a > better way to do dynamic TLS installation, and now as a solution to > the problem of __synccall's use of /proc/self/task being (apparently > hopelessly) broken: > > > > Goal of simplicity and correctness, not micro-optimizing. > > List lock is fully AS-safe. Taking lock requires signals be blocked. To elaborate on this: application signals must be blocked before the lock is taken, but implementation signals (particularly the synccall signal) must not be blocked. Otherwise there is a deadlock: it's possible that thread A is waiting for the thread list lock, and thread B holds the thread list lock and is waiting for thread A to respond to a synccall signal before it can make forward progress. If we want to block *all* signals, which is needed at detached thread exit to prevent delivery in the absence of a stack, they must be blocked after obtaining the thread list lock. Rich
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