linux-kernel - Re: [RFC PATCH 6/7] mm: Remove vmalloc_sync

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Date:   Fri, 8 May 2020 14:58:22 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, hpa@...or.com,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, rjw@...ysocki.net,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC PATCH 6/7] mm: Remove vmalloc_sync_(un)mappings()

On Fri,  8 May 2020 16:40:42 +0200
Joerg Roedel <joro@...tes.org> wrote:

> From: Joerg Roedel <jroedel@...e.de>
> 
> These functions are not needed anymore because the vmalloc and ioremap
> mappings are now synchronized when they are created or teared down.
> 
> Remove all callers and function definitions.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>
>

You'll need to fold this into this patch, as my patch has already hit
Linus's tree.

But I applied your whole series and I'm not able to reproduce the bug.

Tested-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 29615f15a820..1424a89193c6 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8526,19 +8526,6 @@ static int allocate_trace_buffers(struct trace_array *tr, int size)
 	 */
 	allocate_snapshot = false;
 #endif
-
-	/*
-	 * Because of some magic with the way alloc_percpu() works on
-	 * x86_64, we need to synchronize the pgd of all the tables,
-	 * otherwise the trace events that happen in x86_64 page fault
-	 * handlers can't cope with accessing the chance that a
-	 * alloc_percpu()'d memory might be touched in the page fault trace
-	 * event. Oh, and we need to audit all other alloc_percpu() and vmalloc()
-	 * calls in tracing, because something might get triggered within a
-	 * page fault trace event!
-	 */
-	vmalloc_sync_mappings();
-
 	return 0;
 }