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-rw-r--r--patches/source/squashfs-tools/0006-uptream-fix-race.patch54
1 files changed, 54 insertions, 0 deletions
diff --git a/patches/source/squashfs-tools/0006-uptream-fix-race.patch b/patches/source/squashfs-tools/0006-uptream-fix-race.patch
new file mode 100644
index 00000000..3cefbe5b
--- /dev/null
+++ b/patches/source/squashfs-tools/0006-uptream-fix-race.patch
@@ -0,0 +1,54 @@
+commit de03266983ceb62e5365aac84fcd3b2fd4d16e6f
+Author: Phillip Lougher <phillip@squashfs.org.uk>
+Date: Thu Sep 18 01:28:11 2014 +0100
+
+ mksquashfs: fix rare race in fragment waiting in filesystem finalisation
+
+ Fix a rare race condition in fragment waiting when finalising the
+ filesystem. This is a race condition that was initially fixed in 2009,
+ but inadvertantly re-introduced in the latest release when the code
+ was rewritten.
+
+ Background:
+
+ When finalising the filesystem, the main control thread needs to ensure
+ all the in-flight fragments have been queued to the writer thread before
+ asking the writer thread to finish, and then writing the metadata.
+
+ It does this by waiting on the fragments_outstanding counter. Once this
+ counter reaches 0, it synchronises with the writer thread, waiting until
+ the writer thread reports no outstanding data to be written.
+
+ However, the main thread can race with the fragment deflator thread(s)
+ because the fragment deflator thread(s) decrement the fragments_outstanding
+ counter and release the mutex before queueing the compressed fragment
+ to the writer thread, i.e. the offending code is:
+
+ fragments_outstanding --;
+ pthread_mutex_unlock(&fragment_mutex);
+ queue_put(to_writer, write_buffer);
+
+ In extremely rare circumstances, the main thread may see the
+ fragments_outstanding counter is zero before the fragment
+ deflator sends the fragment buffer to the writer thread, and synchronise
+ with the writer thread, and finalise before the fragment has been written.
+
+ The fix is to ensure the fragment is queued to the writer thread
+ before releasing the mutex.
+
+ Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
+
+diff --git a/squashfs-tools/mksquashfs.c b/squashfs-tools/mksquashfs.c
+index 87b7d86..f1fcff1 100644
+--- a/squashfs-tools/mksquashfs.c
++++ b/squashfs-tools/mksquashfs.c
+@@ -2445,8 +2445,8 @@ void *frag_deflator(void *arg)
+ write_buffer->block = bytes;
+ bytes += compressed_size;
+ fragments_outstanding --;
+- pthread_mutex_unlock(&fragment_mutex);
+ queue_put(to_writer, write_buffer);
++ pthread_mutex_unlock(&fragment_mutex);
+ TRACE("Writing fragment %lld, uncompressed size %d, "
+ "compressed size %d\n", file_buffer->block,
+ file_buffer->size, compressed_size);