Hi all,
On Fri, 11 Dec 2020 18:24:53 +1100 Stephen Rothwell <s...@canb.auug.org.au>
wrote:
>
> 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.
>
> 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);This is now a conflict between the userns tree and Linus's tree. -- Cheers, Stephen Rothwell
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