On 03/06/2020 17:17, Vineet Gupta wrote: > On 6/3/20 1:04 PM, Adhemerval Zanella via Libc-alpha wrote: >> >> >> On 03/06/2020 16:46, Vineet Gupta wrote: >>> On 5/29/20 9:49 AM, Adhemerval Zanella via Libc-alpha wrote: >>>>> + ; ----- child starts here --------- >>>>> + >>>>> + ; Setup TP register (only recent kernels v4.19+ do that) >>>>> + and.f 0, r12, CLONE_SETTLS >>>>> + mov.nz r25, r9 >>>> Do you still need to set it since the minimum supported kernel >>>> for ARC is 5.1 ? >>> >>> Right. >>> >>>> It should be safe for internal glibc usage, since for both pthread >>>> and posix_spawn it blocks all signals including SIGCANCEL and SIGXID. >>>> However this is still small race window if this is called directly >>>> with pthread cancellation or g*uid in multithread. >>> >>> I'm not sure what you mean above. Do you mean not doing this in glibc and even if >>> kernel support didn't exist should be safe internally ? >> >> At least for internal clone usage with CLONE_VM within glibc we explicit >> disable all signals (posix_spawn and pthread_create). >> >>> >>> fwiw as mentioned above kernel sets up TP for clone (SETTLS). I detested doing >>> that for a long time, give ABI implications but ended up doing it anyways due to >>> an actual race hit when running uClibc tst-kill6 [1] >> >> We explicit disable all signals during the create_thread call in pthread_create >> (b3cae39dcbfa2432b3f3aa28854d8ac57f0de1b8), so it should not happen on glibc >> anymore. However it is still an issue if application calls clone itself. > > The scenario there was pthread_create() and parent getting scheduled before child > and immediately doing pthread_kill() causing child signal handler to be invoked > and signal handler doing pthread_self() which was broken as TP was not setup. > > With commit above, parent pthread_kill() will block and will only run when child > is scheduled and unblocks the signals ! It could happen with other scenarios when signal plus tp accesses were involved as well: pthread_cancel the thread (since the sigcancel_handler acesses the tp with THREAD_GETMEM macro), setg* functions (since sighandler_setxid), or any functions with a syscall failure that sets the errno. _______________________________________________ linux-snps-arc mailing list linux-snps-arc@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/linux-snps-arc
