On Tue, Feb 12, 2019 at 02:48:38PM -0700, Chris Murphy wrote: > Is it possibly related to the zlib library being used on > Debian/Ubuntu? That you've got even one reproducer with the exact same > hash for the transient error case means it's not hardware or random > error; let alone two independent reproducers.
The errors are not consistent between runs. The above pattern is quite
common, but it is not the only possible output. Add in other processes
reading the 'am' file at the same time and it gets very random.
The bad data tends to have entire extents missing, replaced with zeros.
That leads to a small number of possible outputs (the choices seem to be
only to have the data or have the zeros). It does seem to be a lot more
consistent in recent (post 4.14.80) kernels, which may be interesting.
Here is an example of a diff between two copies of the 'am' file copied
while the repro script was running, filtered through hd:
# diff -u /tmp/f1 /tmp/f2
--- /tmp/f1 2019-02-12 17:05:14.861844871 -0500
+++ /tmp/f2 2019-02-12 17:05:16.883868402 -0500
@@ -56,10 +56,6 @@
*
00020000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
-00021000 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11
|................|
-*
-00022000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
-*
00023000 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12
|................|
*
00024000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
@@ -268,10 +264,6 @@
*
000a0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
-000a1000 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11
|................|
-*
-000a2000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
-*
000a3000 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12
|................|
*
000a4000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
@@ -688,10 +680,6 @@
*
001a0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
-001a1000 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11
|................|
-*
-001a2000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
-*
001a3000 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12
|................|
*
001a4000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
@@ -1524,10 +1512,6 @@
*
003a0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
-003a1000 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11
|................|
-*
-003a2000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
-*
003a3000 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12
|................|
*
003a4000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
@@ -3192,10 +3176,6 @@
*
007a0000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
-007a1000 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11
|................|
-*
-007a2000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
-*
007a3000 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12
|................|
*
007a4000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
@@ -5016,10 +4996,6 @@
*
00c00000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
*
-00c01000 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11
|................|
-*
-00c02000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|................|
-*
[etc...you get the idea]
I'm not sure how the zlib library is involved--sha1sum doesn't use one.
> And then what happens if you do the exact same test but change to zstd
> or lzo? No error? Strictly zlib?
Same errors on all three btrfs compression algorithms (as mentioned in
the original post from August 2018).
> --
> Chris Murphy
>
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