138 lines
4.7 KiB
Diff
138 lines
4.7 KiB
Diff
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From: Jann Horn <jannh@google.com>
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Date: Thu, 4 Apr 2019 23:59:25 +0200
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Subject: tracing: Fix buffer_ref pipe ops
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Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=cffeb9c84d20816a2173e3cfeca210c8bfa8e357
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commit b987222654f84f7b4ca95b3a55eca784cb30235b upstream.
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This fixes multiple issues in buffer_pipe_buf_ops:
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- The ->steal() handler must not return zero unless the pipe buffer has
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the only reference to the page. But generic_pipe_buf_steal() assumes
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that every reference to the pipe is tracked by the page's refcount,
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which isn't true for these buffers - buffer_pipe_buf_get(), which
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duplicates a buffer, doesn't touch the page's refcount.
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Fix it by using generic_pipe_buf_nosteal(), which refuses every
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attempted theft. It should be easy to actually support ->steal, but the
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only current users of pipe_buf_steal() are the virtio console and FUSE,
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and they also only use it as an optimization. So it's probably not worth
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the effort.
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- The ->get() and ->release() handlers can be invoked concurrently on pipe
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buffers backed by the same struct buffer_ref. Make them safe against
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concurrency by using refcount_t.
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- The pointers stored in ->private were only zeroed out when the last
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reference to the buffer_ref was dropped. As far as I know, this
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shouldn't be necessary anyway, but if we do it, let's always do it.
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Link: http://lkml.kernel.org/r/20190404215925.253531-1-jannh@google.com
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Cc: Ingo Molnar <mingo@redhat.com>
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Cc: Masami Hiramatsu <mhiramat@kernel.org>
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Cc: Al Viro <viro@zeniv.linux.org.uk>
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Cc: stable@vger.kernel.org
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Fixes: 73a757e63114d ("ring-buffer: Return reader page back into existing ring buffer")
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Signed-off-by: Jann Horn <jannh@google.com>
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Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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fs/splice.c | 4 ++--
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include/linux/pipe_fs_i.h | 1 +
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kernel/trace/trace.c | 28 ++++++++++++++--------------
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3 files changed, 17 insertions(+), 16 deletions(-)
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--- a/fs/splice.c
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+++ b/fs/splice.c
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@@ -333,8 +333,8 @@ const struct pipe_buf_operations default
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.get = generic_pipe_buf_get,
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};
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-static int generic_pipe_buf_nosteal(struct pipe_inode_info *pipe,
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- struct pipe_buffer *buf)
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+int generic_pipe_buf_nosteal(struct pipe_inode_info *pipe,
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+ struct pipe_buffer *buf)
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{
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return 1;
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}
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--- a/include/linux/pipe_fs_i.h
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+++ b/include/linux/pipe_fs_i.h
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@@ -181,6 +181,7 @@ void free_pipe_info(struct pipe_inode_in
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void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
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int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
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int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
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+int generic_pipe_buf_nosteal(struct pipe_inode_info *, struct pipe_buffer *);
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void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
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void pipe_buf_mark_unmergeable(struct pipe_buffer *buf);
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--- a/kernel/trace/trace.c
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+++ b/kernel/trace/trace.c
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@@ -6800,19 +6800,23 @@ struct buffer_ref {
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struct ring_buffer *buffer;
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void *page;
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int cpu;
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- int ref;
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+ refcount_t refcount;
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};
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+static void buffer_ref_release(struct buffer_ref *ref)
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+{
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+ if (!refcount_dec_and_test(&ref->refcount))
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+ return;
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+ ring_buffer_free_read_page(ref->buffer, ref->cpu, ref->page);
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+ kfree(ref);
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+}
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+
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static void buffer_pipe_buf_release(struct pipe_inode_info *pipe,
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struct pipe_buffer *buf)
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{
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struct buffer_ref *ref = (struct buffer_ref *)buf->private;
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- if (--ref->ref)
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- return;
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-
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- ring_buffer_free_read_page(ref->buffer, ref->cpu, ref->page);
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- kfree(ref);
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+ buffer_ref_release(ref);
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buf->private = 0;
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}
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@@ -6821,7 +6825,7 @@ static void buffer_pipe_buf_get(struct p
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{
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struct buffer_ref *ref = (struct buffer_ref *)buf->private;
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- ref->ref++;
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+ refcount_inc(&ref->refcount);
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}
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/* Pipe buffer operations for a buffer. */
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@@ -6829,7 +6833,7 @@ static const struct pipe_buf_operations
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.can_merge = 0,
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.confirm = generic_pipe_buf_confirm,
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.release = buffer_pipe_buf_release,
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- .steal = generic_pipe_buf_steal,
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+ .steal = generic_pipe_buf_nosteal,
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.get = buffer_pipe_buf_get,
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};
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@@ -6842,11 +6846,7 @@ static void buffer_spd_release(struct sp
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struct buffer_ref *ref =
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(struct buffer_ref *)spd->partial[i].private;
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- if (--ref->ref)
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- return;
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-
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- ring_buffer_free_read_page(ref->buffer, ref->cpu, ref->page);
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- kfree(ref);
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+ buffer_ref_release(ref);
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spd->partial[i].private = 0;
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}
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@@ -6901,7 +6901,7 @@ tracing_buffers_splice_read(struct file
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break;
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}
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- ref->ref = 1;
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+ refcount_set(&ref->refcount, 1);
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ref->buffer = iter->trace_buffer->buffer;
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ref->page = ring_buffer_alloc_read_page(ref->buffer, iter->cpu_file);
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if (IS_ERR(ref->page)) {
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