|author||Rich Felker <firstname.lastname@example.org>||2013-09-20 02:00:27 -0400|
|committer||Rich Felker <email@example.com>||2013-09-20 02:00:27 -0400|
fix potential deadlock bug in libc-internal locking logic
if a multithreaded program became non-multithreaded (i.e. all other threads exited) while one thread held an internal lock, the remaining thread would fail to release the lock. the the program then became multithreaded again at a later time, any further attempts to obtain the lock would deadlock permanently. the underlying cause is that the value of libc.threads_minus_1 at unlock time might not match the value at lock time. one solution would be returning a flag to the caller indicating whether the lock was taken and needs to be unlocked, but there is a simpler solution: using the lock itself as such a flag. note that this flag is not needed anyway for correctness; if the lock is not held, the unlock code is harmless. however, the memory synchronization properties associated with a_store are costly on some archs, so it's best to avoid executing the unlock code when it is unnecessary.
Diffstat (limited to 'arch/arm/bits/setjmp.h')
0 files changed, 0 insertions, 0 deletions