On 2012-05-09 16:27, Michael Tokarev wrote: > On 09.05.2012 23:21, Jan Kiszka wrote: >> On i386, glibc only saves/restores the signal mask via sigprocmask, >> excluding RT signal. A Linux bug in the compat version of this syscall >> corrupts the RT signal state, which will cause lockups of QEMU's VCPU >> threads. > > This should obviously be fixed in kernel, for benefit of all (not only > qemu), do you have any details here?
compat_sys_sigprocmask reads 32-bit sigmask from user space, i.e. excluding RT signal, but calls sys_sigprocmask that takes a 64-bit sigset. So the RT signals are unblocked. I'm testing a simple patch ATM, will post it to LKML once this works. > >> Signed-off-by: Jan Kiszka <jan.kis...@siemens.com> >> --- >> >> I'm not sure where to fall back to. The existing code uses gthread, >> likely because it is the safer harbor. So I picked it as well. > > Can't we resort to the SIGUSR1 workaround for the time being, while > no RT signals are in actual use, and just have the time to let the > kernel side to fix the things up before some actual RTsig user will > emerge in qemu? I think it is a bit more conservative approach, > especially having in mind the minority of users this issue affects > (only 32/64 mixed environment). I'd favor for this variant, and > it looks like I'm the "main" 32/64bit user of qemu in this world :) Most conservative is definitely this patch, not switching to SIGUSR1, hoping that no other RT signal user shows up until current kernel are no longer in use. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
