[PATCH v6 07/13] ARC: Linux Syscall Interface
Wed Jun 3 20:04:28 GMT 2020
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 ?
>> 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 
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.
>  http://lists.infradead.org/pipermail/linux-snps-arc/2018-October/004480.html
More information about the Libc-alpha