From: Jeff Dike In my previous x86_64 thread fix, I forgot to initialize thread.arch.fs in arch_prctl. A process calling arch_prctl to set %fs would lose it on the next context switch. It also turns out that you can switch to a process which is in the process of exiting and which has lost its mm. In this case, it's worse than useless to try to call arch_prctl on the host process. Signed-off-by: Jeff Dike Cc: Paolo 'Blaisorblade' Giarrusso Signed-off-by: Andrew Morton --- arch/um/sys-x86_64/syscalls.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff -puN arch/um/sys-x86_64/syscalls.c~uml-arch_prctl-should-set-thread-fs arch/um/sys-x86_64/syscalls.c --- a/arch/um/sys-x86_64/syscalls.c~uml-arch_prctl-should-set-thread-fs +++ a/arch/um/sys-x86_64/syscalls.c @@ -103,6 +103,9 @@ long arch_prctl_skas(struct task_struct switch(code){ case ARCH_SET_FS: + current->thread.arch.fs = (unsigned long) ptr; + save_registers(pid, ¤t->thread.regs.regs); + break; case ARCH_SET_GS: save_registers(pid, ¤t->thread.regs.regs); break; @@ -140,9 +143,8 @@ long sys_clone(unsigned long clone_flags void arch_switch_to_skas(struct task_struct *from, struct task_struct *to) { - if(to->thread.arch.fs == 0) + if((to->thread.arch.fs == 0) || (to->mm == NULL)) return; arch_prctl_skas(to, ARCH_SET_FS, (void __user *) to->thread.arch.fs); } - _