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authorMike Marshall <hubcap@omnibond.com>2020-04-08 08:52:40 -0400
committerMike Marshall <hubcap@omnibond.com>2020-04-08 09:38:51 -0400
commitec95f1dedc9c64ac5a8b0bdb7c276936c70fdedd (patch)
treecec858112de64a769cd2931fdfa70cdedd6796ca /net/unix
parent7111951b8d4973bda27ff663f2cf18b663d15b48 (diff)
orangefs: get rid of knob code...
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>
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