Re: kern/50430: syscall_disestablish() can remove active syscalls

[christos%zoulas.com@localhost (Christos Zoulas)]

On Nov 16,  5:08pm, uebayasi%gmail.com@localhost (Masao Uebayashi) wrote:
-- Subject: Re: kern/50430: syscall_disestablish() can remove active syscalls

| On Mon, Nov 16, 2015 at 6:45 AM, Christos Zoulas <christos%zoulas.com@localhost> wrote:
| > On Nov 15,  8:25pm, mrg%eterna.com.au@localhost (matthew green) wrote:
| > -- Subject: re: kern/50430: syscall_disestablish() can remove active syscalls
| >
| > |  until bug is fixed, can we disable the autounload?
| >
| > Sure, that sounds prudent. It is difficult to fix properly. One way to do
| > this would be to mark all lwps that have used compat syscalls with a bit
| > depending on the module they have used, and refuse to unload the module
| > until the lwp is gone.
| >
| > - when load a module that has compat syscalls, assign to it a bit.
| > - mark a flags field of all syscalls that were loaded with that module
| >   with that bit.
| > - or the lwp flags with the syscall flags on each syscall.
| > - when it is time to unload check that no lwp has that bit in the flags set.
| > - instead of keeping l_sysent, keep l_sysmodflags or something.
| 
| What happens if signal handler does longjmp(3) and interrupted syscall
| never returns?

It does not matter. The flag is never cleared (even when that does not
happen). Once an lwp executes a syscall from a compat module, that module
cannot be unloaded until the lwp exits.

christos