Revert switch of env locking to rwlock, to fix deadlock in process spawning #82877
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@bors r+ rollup=never |
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📌 Commit acdca31 has been approved by |
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@bors r+ Thanks for investigating! Let's open an issue to check out the underlying problem that's probably still there with a Mutex. Once we fix that part, we can probably put the rwlock back. (Not unlocking in the child by mem::forget'ing the guard might already be enough.) |
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Oh. Review race condition. |
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@bors p=1 To avoid further CI timeouts. |
Filed #82879 to track this. |
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⌛ Testing commit acdca31 with merge 970337fe14c426faa0bf26e21a4038065531ca59... |
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💔 Test failed - checks-actions |
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I saw this failure on #82847 (comment), spurious? |
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⌛ Testing commit acdca31 with merge f6fb3c23628c09c43b485e0d41578923e14af5a5... |
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@JohnTitor I can reproduce that error, so I filed #82886. |
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⌛ Testing commit acdca31 with merge f874496963709b086adf4a337be49ea6ff959119... |
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@bors retry |
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⌛ Testing commit acdca31 with merge 81b67ade8411474035c922911d623345fadbd59f... |
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@bors p=20 (To make it go in front of rollups.) |
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Mar 15, 2021
use RWlock when accessing os::env (take 2) This reverts commit acdca31 (rust-lang#82877) i.e. redoes rust-lang#81850 since the invalid unlock attempts in the child process have been fixed in rust-lang#82949 r? `@joshtriplett`
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This reverts commit 354f19c, reversing changes made to 0cfba2f.
PR #81850 switched the environment lock from a mutex to an rwlock. However, process spawning (when not able to use
posix_spawn) locks the environment before forking, and unlocks it after forking (in both the parent and the child). With a mutex, this works (although probably not correct even with a mutex). With an rwlock, on at least some targets, unlocking in the child does not work correctly, resulting in a deadlock.This has manifested as CI hangs on i686 Linux; that target doesn't use
posix_spawnin the CI environment due to the age of the installed C library (currently glibc 2.23). (Switching toposix_spawnwould just mask this issue, though, which would still arise in any case that can't useposix_spawn.)Some additional cleanup of environment handling around process spawning may help, but for now, revert the PR and go back to a standard mutex.
Fixes #82221