On 20.12.2015 15:11, Mathieu Desnoyers wrote: > ----- On Dec 19, 2015, at 5:37 AM, Helge Deller deller@xxxxxx wrote: > >> Hi Mathieu, >> >> On 18.12.2015 21:42, Helge Deller wrote: >>> On 18.12.2015 20:58, Mathieu Desnoyers wrote: >>>>>>> When testing liburcu on a 3.18 Linux kernel, 2-core MIPS (cpu model : >>>>>>> Ingenic JZRISC V4.15 FPU V0.0), we notice that a blocked sys_futex >>>>>>> FUTEX_WAIT returns -1, errno=ENOSYS when interrupted by a SA_RESTART >>>>>>> signal handler. This spurious ENOSYS behavior causes hangs in liburcu >>>>>>> 0.9.x. Running a MIPS 3.18 kernel under a QEMU emulator exhibits the >>>>>>> same behavior. This might affect earlier kernels. >>>>>>> >>>>>>> This issue appears to be fixed in 3.18.y stable kernels and 3.19, but >>>>>>> nevertheless, we should try to handle this kernel bug more gracefully >>>>>>> than a user-space hang due to unexpected spurious ENOSYS return value. >>>>>> >>>>>> It's actually fixed in 3.19, but not in 3.18.y stable kernels. The >>>>>> Linux kernel upstream fix commit is: >>>>>> e967ef02 "MIPS: Fix restart of indirect syscalls" >> >>>> Looks like parisc has an issue very similar to the one that >>>> has been fixed on MIPS by e967ef02 "MIPS: Fix restart of indirect syscalls". >> >> Yes, parisc is affected the same way. >> I've posted a patch to the parisc mailing list which fixes this issue for >> parisc and which I plan to push into stable kernels: >> http://thread.gmane.org/gmane.linux.ports.parisc/26243 >> >> Regarding your patch for liburcu: >> >>>>>>> Therefore, fallback on the "async-safe" version of compat_futex in those >>>>>>> situations where FUTEX_WAIT returns ENOSYS. This async-safe fallback has >>>>>>> the nice property of being OK to use concurrently with other FUTEX_WAKE >>>>>>> and FUTEX_WAIT futex() calls, because it's simply a busy-wait scheme. >> >> I've tested your patch. It does not produce any regressions on parisc, but I >> can't >> say for sure if it really works. ENOSYS is returned randomly, so maybe I didn't >> faced a situation where your patch actually was used. > > If you ran make check and make regtest, and nothing > fails/hangs, you should be OK. Yes, I did run both. > liburcu runs very heavy > stress-tests which makes it likely to hit race conditions > repeatedly. Helge -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
