fix: Fix lock order inversion / deadlock (backport #1010) - #1015
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This fixes a deadlock if a guard condition was triggered while a guard condition was being attached or detached. Signed-off-by: Janosch Machowinski <J.Machowinski@cellumation.com> Co-authored-by: Janosch Machowinski <J.Machowinski@cellumation.com> (cherry picked from commit c5c101a)
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Signed-off-by: Alejandro Hernandez Cordero <ahcorde@gmail.com>
ahcorde
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Jul 20, 2026
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check_and_attach_condition() ends by writing wait_set_data->triggered = false based on a comment asserting that rmw_wait() holds condition_mutex across the call. That precondition was removed by ros2#1005 (backported to humble as ros2#1015), which deliberately drops the lock around check_and_attach_condition() to avoid the ABBA deadlock in ros2#998. The write is now unsynchronized and races with the notifier paths, which set triggered = true while holding condition_mutex. If a message is delivered after its entity has been attached but before check_and_attach_condition() returns, the trailing write clears the flag, rmw_wait() then evaluates its predicate as false and blocks on the condition variable with data already queued. The reset is redundant in any case: rmw_wait() sets triggered = false under condition_mutex immediately before calling this function. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Description
Lyrical backport of #1005
This is an automatic backport of pull request #1010 done by [Mergify](https://mergify.com).