Russell King was reporting lots of warnings when he compiled his kernel
with ftrace enabled. With some investigation it was discovered that it
was his compile setup. He was using ccache with hard links, which allowed
recordmcount to process the same .o twice. When this happens, recordmcount
will detect that it was already done and give a warning about it.
Russell fixed this by having recordmcount detect that the object file
has more than one hard link, and if it does, it unlinks the object file
after it maps it and processes then. This appears to fix the issue.
As you did not like the fact that recordmcount modified the file in place
and thought that it should do the modifications in memory and then write
it out to disk and move it over the old file to prevent other more subtle
issues like the one above, a second patch is added on top of Russell's to
do just that. Luckily the original code had write and lseek wrappers that
I was able to modify to not do inplace writes, but simply keep track
of the changes made in memory. When a write is made, a "update" flag is
set, and at the end of processing, if the update is set, then it writes
the file with changes out to a new file, and then renames it over the
original one.
The file descriptor is still passed to the write and lseek wrappers because
removing that would cause the change to be more intrusive. That can be
removed in a follow up cleanup patch that can wait till the next merge
window.
ftrace/scripts: Have recordmcount copy the object file
Russell King found that he had weird side effects when compiling the kernel
with hard linked ccache. The reason was that recordmcount modified the
kernel in place via mmap, and when a file gets modified twice by
recordmcount, it will complain about it. To fix this issue, Russell wrote a
patch that checked if the file was hard linked more than once and would
unlink it if it was.
Linus Torvalds was not happy with the fact that recordmcount does this in
place modification. Instead of doing the unlink only if the file has two or
more hard links, it does the unlink all the time. In otherwords, it always
does a copy if it changed something. That is, it does the write out if a
change was made.
Cc: stable@vger.kernel.org # 2.6.37+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
1 file changed
