[tip: sched/urgent] rseq: Eliminate useless task_work on execve

[tip-bot2 for Mathieu Desnoyers]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     169eae7711ea4b745e2d33d53e7b88689b10e1a0
Gitweb:        https://git.kernel.org/tip/169eae7711ea4b745e2d33d53e7b88689b10e1a0
Author:        Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
AuthorDate:    Thu, 27 Mar 2025 09:29:45 -04:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 03 Apr 2025 13:10:47 +02:00

rseq: Eliminate useless task_work on execve

Eliminate a useless task_work on execve by moving the call to
rseq_set_notify_resume() from sched_mm_cid_after_execve() to the error
path of bprm_execve().

The call to rseq_set_notify_resume() from sched_mm_cid_after_execve() is
pointless in the success case, because rseq_execve() will clear the rseq
pointer before returning to userspace.

sched_mm_cid_after_execve() is called from both the success and error
paths of bprm_execve(). The call to rseq_set_notify_resume() is needed
on error because the mm_cid may have changed.

Also move the rseq_execve() to right after sched_mm_cid_after_execve()
in bprm_execve().

[ mingo: Merged to a recent upstream kernel, extended the changelog. ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250327132945.1558783-1-mathieu.desnoyers@xxxxxxxxxxxx
---
 fs/exec.c           | 3 ++-
 kernel/sched/core.c | 1 -
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 5d1c0d2..8e4ea5f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1864,9 +1864,9 @@ static int bprm_execve(struct linux_binprm *bprm)
 		goto out;
 
 	sched_mm_cid_after_execve(current);
+	rseq_execve(current);
 	/* execve succeeded */
 	current->in_execve = 0;
-	rseq_execve(current);
 	user_events_execve(current);
 	acct_update_integrals(current);
 	task_numa_free(current, false);
@@ -1883,6 +1883,7 @@ out:
 		force_fatal_sig(SIGSEGV);
 
 	sched_mm_cid_after_execve(current);
+	rseq_set_notify_resume(current);
 	current->in_execve = 0;
 
 	return retval;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index cfaca30..c81cf64 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10703,7 +10703,6 @@ void sched_mm_cid_after_execve(struct task_struct *t)
 		smp_mb();
 		t->last_mm_cid = t->mm_cid = mm_cid_get(rq, t, mm);
 	}
-	rseq_set_notify_resume(t);
 }
 
 void sched_mm_cid_fork(struct task_struct *t)