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sockets.c: Make sock_inc_used overflow check robust.

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Before this patch, it was possible that the overflow check might
miss an overflow event.

e.g. Consider 2 threads, both executing this method. u8_t fd_used is on 255...

Thread A -> atomically increment fd_used (which is now 0)
Thread B -> atomically increment fd_used (which is now 1)
Thread A -> check overflow... sees everything ok
Thread B -> check overflow... sees everything ok

And the overflow is missed :(

Signed-off-by: goldsimon <goldsimon@gmx.de>
This commit is contained in:
Tim Cussins 2017-04-18 15:36:14 +01:00 committed by goldsimon
parent 7ac3056da9
commit 8e83e206f4
1 changed files with 6 additions and 1 deletions
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7
src/api/sockets.c
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@ -374,9 +374,14 @@ lwip_socket_thread_cleanup(void)
static void
sock_inc_used(struct lwip_sock *sock)
{
SYS_ARCH_DECL_PROTECT(lev);
LWIP_ASSERT("sock != NULL", sock != NULL);
SYS_ARCH_INC(sock->fd_used, 1);
SYS_ARCH_PROTECT(lev);
++sock->fd_used;
LWIP_ASSERT("sock->fd_used != 0", sock->fd_used != 0);
SYS_ARCH_UNPROTECT(lev);
}
/* In full-duplex mode,sock->fd_used != 0 prevents a socket descriptor from being