Subject: linux-next: manual merge of the userns tree with the tip tree

From: Stephen Rothwell <[email-masked]>
Date: Fri, 11 Dec 2020 18:24:53 +1100

Hi all,

Today's linux-next merge of the userns tree got a conflict in:

  kernel/events/core.c

between commit:

  78af4dc949da ("perf: Break deadlock involving exec_update_mutex")

from the tip tree and commit:

  f7cfd871ae0c ("exec: Transform exec_update_mutex into a rw_semaphore")

from the userns tree.

I fixed it up (see below) and can carry the fix as necessary. This
is now fixed as far as linux-next is concerned, but any non trivial
conflicts should be mentioned to your upstream maintainer when your tree
is submitted for merging.  You may also want to consider cooperating
with the maintainer of the conflicting tree to minimise any particularly
complex conflicts.

-- 
Cheers,
Stephen Rothwell

diff --cc kernel/events/core.c
index 19ae6c931c52,55b2330b556c..000000000000
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@@ -11958,24 -11864,6 +11958,24 @@@ SYSCALL_DEFINE5(perf_event_open
  		goto err_context;
  	}
  
 +	if (task) {
- 		err = mutex_lock_interruptible(&task->signal->exec_update_mutex);
++		err = down_read_interruptible(&task->signal->exec_update_lock);
 +		if (err)
 +			goto err_file;
 +
 +		/*
 +		 * Preserve ptrace permission check for backwards compatibility.
 +		 *
- 		 * We must hold exec_update_mutex across this and any potential
++		 * We must hold exec_update_lock across this and any potential
 +		 * perf_install_in_context() call for this new event to
 +		 * serialize against exec() altering our credentials (and the
 +		 * perf_event_exit_task() that could imply).
 +		 */
 +		err = -EACCES;
 +		if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
 +			goto err_cred;
 +	}
 +
  	if (move_group) {
  		gctx = __perf_event_ctx_lock_double(group_leader, ctx);
  
@@@ -12151,10 -12039,7 +12151,10 @@@ err_locked
  	if (move_group)
  		perf_event_ctx_unlock(group_leader, gctx);
  	mutex_unlock(&ctx->mutex);
 -/* err_file: */
 +err_cred:
 +	if (task)
- 		mutex_unlock(&task->signal->exec_update_mutex);
++		up_read(&task->signal->exec_update_lock);
 +err_file:
  	fput(event_file);
  err_context:
  	perf_unpin_context(ctx);