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 ! _______________________________________________ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc
