On 07/22/2014 10:52 PM, Michael Cree wrote: > Running strace on nptl/tst-eintr3 reveals that the clone() syscall > is retried by the kernel if an ERESTARTNOINTR error occurs. At > $syscall_error in arch/alpha/kernel/entry.S the kernel handles the > error and in doing that it writes to 72(sp) which is where the value > of the a3 CPU register on entry to the kernel is stored. Then the > kernel retries the clone() function. But the alpha specific code > for copy_thread() in arch/alpha/kernel/process.c does not use the > passed a3 cpu register (the argument tls), instead it goes to the > saved stack to get the value of the a3 register, which on the > second call to clone() has been modified to no longer be the value > of the a3 cpu register on entry to the kernel. And a latent bomb > is laid for userspace in the form of an incorrect process unique > value (which is the thread pointer) in the PCB. > > Am I correct in my analysis and, if so, can we get a fix for this > please. Well... let me start with the assumption that we can't possibly restart unless the syscall fails with -ERESTART*. Before we clobber 72($sp), $syscall_error saves the old value in $19. This is the r19 parameter to do_work_pending, and is passed all the way down to syscall_restart where we do restore the original value of a3 for ERESTARTNOINTR. So if there's a path that leads to restart, but doesn't save a3 before clobbering, I don't see it. Do you have an strace dump that shows this? r~ -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
