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Christoph Hellwig sent in a reversion of "orangefs: remember count
when reading." because:
->read_iter calls can race with each other and one or
more ->flush calls. Remove the the scheme to store the read
count in the file private data as is is completely racy and
can cause use after free or double free conditions
Christoph's reversion caused Orangefs not to work or to compile. I
added a patch that fixed that, but intel's kbuild test robot pointed
out that sending Christoph's patch followed by my patch upstream, it
would break bisection because of the failure to compile. So I have
combined the reversion plus my patch... here's the commit message
that was in my patch:
Logically, optimal Orangefs "pages" are 4 megabytes. Reading
large Orangefs files 4096 bytes at a time is like trying to
kick a dead whale down the beach. Before Christoph's "Revert
orangefs: remember count when reading." I tried to give users
a knob whereby they could, for example, use "count" in
read(2) or bs with dd(1) to get whatever they considered an
appropriate amount of bytes at a time from Orangefs and fill
as many page cache pages as they could at once.
Without the racy code that Christoph reverted Orangefs won't
even compile, much less work. So this replaces the logic that
used the private file data that Christoph reverted with
a static number of bytes to read from Orangefs.
I ran tests like the following to determine what a
reasonable static number of bytes might be:
dd if=/pvfsmnt/asdf of=/dev/null count=128 bs=4194304
dd if=/pvfsmnt/asdf of=/dev/null count=256 bs=2097152
dd if=/pvfsmnt/asdf of=/dev/null count=512 bs=1048576
.
.
.
dd if=/pvfsmnt/asdf of=/dev/null count=4194304 bs=128
Reads seem faster using the static number, so my "knob code"
wasn't just racy, it wasn't even a good idea...
Signed-off-by: Mike Marshall <hubcap@omnibond.com>
Reported-by: kbuild test robot <lkp@intel.com>
Linux kernel
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