Decouple the semcount and the work queue length.
Previous Problem:
If a work is queued and cancelled in high priority threads (or queued
by timer and cancelled by another high priority thread) before
work_thread runs, the queue operation will mark work_thread as ready to
run, but the cancel operation minus the semcount back to -1 and makes
wqueue->q empty. Then the work_thread still runs, found empty queue,
and wait sem again, then semcount becomes -2 (being minused by 1)
This can be done multiple times, then semcount can become very small
value. Test case to produce incorrect semcount:
high_priority_task()
{
for (int i = 0; i < 10000; i++)
{
work_queue(LPWORK, &work, worker, NULL, 0);
work_cancel(LPWORK, &work);
usleep(1);
}
/* Now the g_lpwork.sem.semcount is a value near -10000 */
}
With incorrect semcount, any queue operation when the work_thread is
busy, will only increase semcount and push work into queue, but cannot
trigger work_thread (semcount is negative but work_thread is not
waiting), then there will be more and more works left in queue while
the work_thread is waiting sem and cannot call them.
Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
Squashed commit of the following:
Fix up some final compile isses.
net/netdev: Convert the network down notification logic to use the new wqueue-based notification factility.
net/udp: Convert the UDP readahead notification logic to use the new wqueue-based notification factility.
net/tcp: Convert the TCP readahead notification logic to use the new wqueue-based notification factility.
mm/iob: Convert the IOB notification logic to use the new wqueue-based notification factility.
sched/wqueue: Signals are not good IPCs to support the target poll functionality for several reasons including the amount of data that can be passed with a signal and in the fact that in protected and kernel modes, user threads executing signal handlers in protected, kernel memory is problematic. Instead, convert the same logic to perform the notifications via function callback on the high priority work queue.
sched/wqueue: Modify high priority work queue to support multiple threads.
sched/wqueue and libs/libc/wqueue: workqueues don't need set global data to zero since .bss is cleared automatically. Removing this unnecessary initialization also avoids the loss the work items queued before initialization.
Squashed commit of the following:
sched: Rename all use of system_t to clock_t.
syscall: Rename all use of system_t to clock_t.
net: Rename all use of system_t to clock_t.
libs: Rename all use of system_t to clock_t.
fs: Rename all use of system_t to clock_t.
drivers: Rename all use of system_t to clock_t.
arch: Rename all use of system_t to clock_t.
include: Remove definition of systime_t; rename all use of system_t to clock_t.
