summaryrefslogtreecommitdiff
path: root/user/squashfs-tools/0001-mksquashfs-fix-rare-race-in-fragment-waiting-in-file.patch
diff options
context:
space:
mode:
authorA. Wilcox <AWilcox@Wilcox-Tech.com>2018-07-05 20:25:27 -0500
committerA. Wilcox <AWilcox@Wilcox-Tech.com>2018-07-05 20:25:27 -0500
commit25dbded13a57b4bae4ba219a5d2874b7035d389e (patch)
tree32498743c47caff20449cc0e894edf1a59ff48f1 /user/squashfs-tools/0001-mksquashfs-fix-rare-race-in-fragment-waiting-in-file.patch
parentbe94847a164f9ae0d58332b1de3ed8b037e2fc14 (diff)
downloadpackages-25dbded13a57b4bae4ba219a5d2874b7035d389e.tar.gz
packages-25dbded13a57b4bae4ba219a5d2874b7035d389e.tar.bz2
packages-25dbded13a57b4bae4ba219a5d2874b7035d389e.tar.xz
packages-25dbded13a57b4bae4ba219a5d2874b7035d389e.zip
user/squashfs-tools: pull in, fix, take
Diffstat (limited to 'user/squashfs-tools/0001-mksquashfs-fix-rare-race-in-fragment-waiting-in-file.patch')
-rw-r--r--user/squashfs-tools/0001-mksquashfs-fix-rare-race-in-fragment-waiting-in-file.patch60
1 files changed, 60 insertions, 0 deletions
diff --git a/user/squashfs-tools/0001-mksquashfs-fix-rare-race-in-fragment-waiting-in-file.patch b/user/squashfs-tools/0001-mksquashfs-fix-rare-race-in-fragment-waiting-in-file.patch
new file mode 100644
index 000000000..51f588818
--- /dev/null
+++ b/user/squashfs-tools/0001-mksquashfs-fix-rare-race-in-fragment-waiting-in-file.patch
@@ -0,0 +1,60 @@
+From de03266983ceb62e5365aac84fcd3b2fd4d16e6f Mon Sep 17 00:00:00 2001
+From: Phillip Lougher <phillip@squashfs.org.uk>
+Date: Thu, 18 Sep 2014 01:28:11 +0100
+Subject: [PATCH] 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>
+---
+ squashfs-tools/mksquashfs.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+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
+@@ -2419,8 +2419,8 @@ 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);
+--
+2.10.2
+