[lwip-devel] [bug #26405] Prematurely released semaphore causes lwip_select() to crash

[Simon Goldschmidt]

Follow-up Comment #2, bug #26405 (project lwip):

Reading the code, I don't get how it could go wrong:

tcpip_thread calls:
    sys_sem_signal(selectsem);
    sys_sem_signal(scb->sem);
while the application thread calls:
    i = sys_sem_wait_timeout(select_cb.sem, msectimeout);
    sys_sem_wait(selectsem);
    sys_sem_signal(selectsem);
    sys_sem_free(select_cb.sem);

The only problem I see here is that the port used by Konstantin could maybe
ignore the int parameter passed to sys_sem_new and always initialize the
semaphore with 1, in which case it would wait only for selectsem... but that
would make problems elswhere, too.

Anyway, since it's good practice (or at least that's what I've learnt:) to
use resources in the same order in every place, I don't have that strong an
opinion against changing the order of the sys_sem_signal calls...
Nevertheless, I'd like to understand the bug before making the change.

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