[lwip-devel] [bug #65996] tcp_output() crashes in multithread system

[Andrey Vinogradov]

URL:
  <https://savannah.nongnu.org/bugs/?65996>

                 Summary: tcp_output() crashes in multithread system
                   Group: lwIP - A Lightweight TCP/IP stack
               Submitter: andreyvinogradov
               Submitted: Tue 16 Jul 2024 04:43:56 PM UTC
                Category: TCP
                Severity: 3 - Normal
              Item Group: Crash Error
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: git head


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Follow-up Comments:


-------------------------------------------------------
Date: Tue 16 Jul 2024 04:43:56 PM UTC By: Andrey Vinogradov <andreyvinogradov>
Program can call tcp_output() from tcp_input() from input interrupt exact in
same time tcp_output() already in progress.

I constantly reproduce problem in tcp_output() with pcb->unacked turning form
NULL to nonNULL right after nullptr check.

You need to add mutex befor tcp_output() call if program work in several
threads. For example:
```
static inline err_t
do_tcp_output(struct tcp_pcb *pcb)
{
// tcp_output() code here
...
}

err_t
tcp_output(struct tcp_pcb *pcb) {
  static u8_t tcp_out_lock = 0;

  while (tcp_out_lock) {
  }
  tcp_out_lock = 1;

  err_t res = do_tcp_output(pcb);
  tcp_out_lock = 0;
  return res;
}
```







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