From: Julia Cartwright Date: Mon, 7 May 2018 08:58:57 -0500 Subject: [PATCH 173/353] squashfs: make use of local lock in multi_cpu decompressor Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=1b53a7e12286b2e587e9bea1c4ab5ab4ebc5c892 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 Tested-by: Alexander Stein Signed-off-by: Julia Cartwright Signed-off-by: Sebastian Andrzej Siewior --- fs/squashfs/decompressor_multi_percpu.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/fs/squashfs/decompressor_multi_percpu.c b/fs/squashfs/decompressor_multi_percpu.c index 23a9c28ad8ea..6a73c4fa88e7 100644 --- a/fs/squashfs/decompressor_multi_percpu.c +++ b/fs/squashfs/decompressor_multi_percpu.c @@ -10,6 +10,7 @@ #include #include #include +#include #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_sb_info *msblk, struct buffer_head **bh, { 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",