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From: Julia Cartwright <julia@ni.com>
Date: Mon, 7 May 2018 08:58:57 -0500
Subject: [PATCH] squashfs: make use of local lock in multi_cpu
decompressor
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.7-rt5.tar.xz
Currently, the squashfs multi_cpu decompressor makes use of
get_cpu_ptr()/put_cpu_ptr(), which unconditionally disable preemption
during decompression.
Because the workload is distributed across CPUs, all CPUs can observe a
very high wakeup latency, which has been seen to be as much as 8000us.
Convert this decompressor to make use of a local lock, which will allow
execution of the decompressor with preemption-enabled, but also ensure
concurrent accesses to the percpu compressor data on the local CPU will
be serialized.
Cc: stable-rt@vger.kernel.org
Reported-by: Alexander Stein <alexander.stein@systec-electronic.com>
Tested-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Julia Cartwright <julia@ni.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
fs/squashfs/decompressor_multi_percpu.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
--- a/fs/squashfs/decompressor_multi_percpu.c
+++ b/fs/squashfs/decompressor_multi_percpu.c
@@ -10,6 +10,7 @@
#include <linux/slab.h>
#include <linux/percpu.h>
#include <linux/buffer_head.h>
+#include <linux/locallock.h>
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
@@ -25,6 +26,8 @@ struct squashfs_stream {
void *stream;
};
+static DEFINE_LOCAL_IRQ_LOCK(stream_lock);
+
void *squashfs_decompressor_create(struct squashfs_sb_info *msblk,
void *comp_opts)
{
@@ -79,10 +82,15 @@ int squashfs_decompress(struct squashfs_
{
struct squashfs_stream __percpu *percpu =
(struct squashfs_stream __percpu *) msblk->stream;
- struct squashfs_stream *stream = get_cpu_ptr(percpu);
- int res = msblk->decompressor->decompress(msblk, stream->stream, bh, b,
- offset, length, output);
- put_cpu_ptr(stream);
+ struct squashfs_stream *stream;
+ int res;
+
+ stream = get_locked_ptr(stream_lock, percpu);
+
+ res = msblk->decompressor->decompress(msblk, stream->stream, bh, b,
+ offset, length, output);
+
+ put_locked_ptr(stream_lock, stream);
if (res < 0)
ERROR("%s decompression failed, data probably corrupt\n",
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