identical hashes on two branches, but holes in git log

[Philippe De Muyter <phdm@macq.eu>]

Hello,

I work on the linux kernel sources (with origin = linux-stable) and I
have my local branch (the one with my local patches) supposedly based
on v3.14.  But actually if I invoke "git diff v3.14", I get much more
diffs than my own patches.

Trying to understand, I have eventually done "git log" on my branch and
on v3.15 with the following commands :

git log v3.15 --full-history --decorate=short | grep '^commit' > /tmp/3.15.commits
git log --full-history --decorate=short | grep '^commit' > /tmp/mybranch.commits

I compare then the two histories with

diff -u /tmp/3.15.commits /tmp/mybranch.commits

and I get (excerpt) :

--- /tmp/3.15.commits      2015-05-19 13:19:59.665205514 +0200
+++ /tmp/mybranch.commits     2015-05-19 13:19:52.452081328 +0200
@@ -1,3780 +1,84 @@
-commit 1860e379875dfe7271c649058aeddffe5afd9d0d (tag: v3.15)
-commit ...
...
-commit fad01e866afdbe01a1f3ec06a39c3a8b9e197014 (tag: v3.15-rc8)
...
...
-commit c9eaa447e77efe77b7fa4c953bd62de8297fd6c5 (tag: v3.15-rc1)
...
-commit 57673c2b0baa900dddae3b9eb3d7748ebf550eb3
+commit a1fb433346cb5733945b5fc243f7334744bae4fd (HEAD, macq_boards-3.14.0)
+commit ...
...
+commit 2be7b20bbb337e0031e0f0d39c9a4845b6bbf3b8
 commit 455c6fdbd219161bd09b1165f11699d6d73de11c (tag: v3.14)	==== identical commit
-commit c32fc9c803f8ed90a7548810de48ca33a3020168		==== commit missing in my branch
 commit fedc1ed0f11be666de066b0c78443254736a942e		==== more identical commits
 commit 01358e562a8b97f50ec04025c009c71508e6d373
 commit 915ac4e26ef9c39a0f831e935509243732abedc0
@@ -3784,4289 +88,252 @@
 commit 0b1b901b5a98bb36943d10820efc796f7cd45ff3
 commit 1d6a32acd70ab18499829c0a9a5dbe2bace72a13
 commit 0818bf27c05b2de56c5b2bd08cfae2a939bd5f52
-commit 877e1f1529a5c4fcc8460c1317c753ff8a6874c5		==== more missing commits
-commit 57918dfadf717acf7d0488d5970c56a282d0aad1
-commit 86ea5e6b793d45fa7d2aa504ac3aefc813f0fd55
-commit a5dde0c72ccbb0f66b3491ee83f4c579aea0651d
-commit c7f6ee264b511d8a35063e9821cf36ad18e4e4fd
...
-commit c99abc8b39d8281dad04d771bb7a2de36fec4d9f
 commit b098d6726bbfb94c06d6e1097466187afddae61f (tag: v3.14-rc8) ==== more identical commits
 commit 822316461b15e0207e50ff661f9cf830af116e9f
 commit 56f1f4b24e8787d7ba794dbe2e949d504c054892
...

How is that possible (to have the same commit, with the same hash but
different ancestors), and how can I recover from that situation ?

I really would like to rebase my branch on v3.14, but it says it is already !

I have also done a 'git fsck'.  It has shown only 

Checking object directories: 100% (256/256), done.                                                                                         
Checking objects: 100% (4566799/4566799), done.                                                                                            
Checking connectivity: 4494119, done
dangling tree ...
dangling commit ...
dangling blob ...

This is with git version 1.7.10.4

TIA

Philippe

-- 
Philippe De Muyter +32 2 6101532 Macq SA rue de l'Aeronef 2 B-1140 Bruxelles