[PATCH 5/7] exec: In setup_new_exec cache current in the local variable me

[Eric W. Biederman]

At least gcc 8.3 when generating code for x86_64 has a hard time
consolidating multiple calls to current aka get_current(), and winds
up unnecessarily rereading %gs:current_task several times in
setup_new_exec.

Caching the value of current in the local variable of me generates
slightly better and shorter assembly.

Signed-off-by: "Eric W. Biederman" <ebied...@xmission.com>
---
 fs/exec.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 93e40f865523..8c3abafb9bb1 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1391,6 +1391,7 @@ EXPORT_SYMBOL(would_dump);
 
 void setup_new_exec(struct linux_binprm * bprm)
 {
+       struct task_struct *me = current;
        /*
         * Once here, prepare_binrpm() will not be called any more, so
         * the final state of setuid/setgid/fscaps can be merged into the
@@ -1400,7 +1401,7 @@ void setup_new_exec(struct linux_binprm * bprm)
 
        if (bprm->secureexec) {
                /* Make sure parent cannot signal privileged process. */
-               current->pdeath_signal = 0;
+               me->pdeath_signal = 0;
 
                /*
                 * For secureexec, reset the stack limit to sane default to
@@ -1413,9 +1414,9 @@ void setup_new_exec(struct linux_binprm * bprm)
                        bprm->rlim_stack.rlim_cur = _STK_LIM;
        }
 
-       arch_pick_mmap_layout(current->mm, &bprm->rlim_stack);
+       arch_pick_mmap_layout(me->mm, &bprm->rlim_stack);
 
-       current->sas_ss_sp = current->sas_ss_size = 0;
+       me->sas_ss_sp = me->sas_ss_size = 0;
 
        /*
         * Figure out dumpability. Note that this checking only of current
@@ -1431,18 +1432,18 @@ void setup_new_exec(struct linux_binprm * bprm)
 
        arch_setup_new_exec();
        perf_event_exec();
-       __set_task_comm(current, kbasename(bprm->filename), true);
+       __set_task_comm(me, kbasename(bprm->filename), true);
 
        /* Set the new mm task size. We have to do that late because it may
         * depend on TIF_32BIT which is only updated in flush_thread() on
         * some architectures like powerpc
         */
-       current->mm->task_size = TASK_SIZE;
+       me->mm->task_size = TASK_SIZE;
 
        /* An exec changes our domain. We are no longer part of the thread
           group */
-       WRITE_ONCE(current->self_exec_id, current->self_exec_id + 1);
-       flush_signal_handlers(current, 0);
+       WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);
+       flush_signal_handlers(me, 0);
 
        /*
         * install the new credentials for this executable
@@ -1458,16 +1459,16 @@ void setup_new_exec(struct linux_binprm * bprm)
         * wait until new credentials are committed
         * by commit_creds() above
         */
-       if (get_dumpable(current->mm) != SUID_DUMP_USER)
-               perf_event_exit_task(current);
+       if (get_dumpable(me->mm) != SUID_DUMP_USER)
+               perf_event_exit_task(me);
        /*
         * cred_guard_mutex must be held at least to this point to prevent
         * ptrace_attach() from altering our determination of the task's
         * credentials; any time after this it may be unlocked.
         */
        security_bprm_committed_creds(bprm);
-       mutex_unlock(&current->signal->exec_update_mutex);
-       mutex_unlock(&current->signal->cred_guard_mutex);
+       mutex_unlock(&me->signal->exec_update_mutex);
+       mutex_unlock(&me->signal->cred_guard_mutex);
 }
 EXPORT_SYMBOL(setup_new_exec);
 
-- 
2.20.1