Previously, when the result of a try-lock call is branched on more than
once, the paths between the branches would disagree on whether the
capability is held while remaining consistent at each branch. The analysis
then gave a false positive warning at the intermediate join:
mutex 'lock' is not held on every path through here
Create getTerminatorTrylockCall() helper from getEdgeLockset(); if the terminator
of a block branches on the result of a call to a try_acquire_capability-function
(perhaps negated or stored in a local variable), this helper returns that call and
its callee.
Use this new helper in getTerminatorTrylockCaps(), which will return the
capabilities acquired by a trylock; feed these capabilites to intersectAndWarn()
during a branch join, in order to avoid false positives.
Soundness is preserved because intersectAndWarn() still removes the
capabilities from the join block's entry lockset, ensuring any guarded access
inside the join block before the terminator is diagnosed. getEdgeLockset()
then re-adds the capability on the success edge.
This change resolves the false positive warning reported in [1].
Reported-by: https://lore.kernel.org/linux-fsdevel/20260714181057.667977-1-timday@thelustrecollective.com/ [1]
Assisted-by: AI was used a bit to understand the code and to help with testing and validation
Timothy Day
a0177f77dd