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    SubjectRE: [PATCH] stm class: increase pos if no free channels found
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    > -----Original Message-----
    > From: Alexander Shishkin [mailto:alexander.shishkin@linux.intel.com]
    > Sent: Monday, October 15, 2018 3:43 PM
    > To: Jin, Zhi <zhi.jin@intel.com>
    > Cc: linux-kernel@vger.kernel.org; Jin, Zhi <zhi.jin@intel.com>
    > Subject: Re: [PATCH] stm class: increase pos if no free channels found
    >
    > Zhi Jin <zhi.jin@intel.com> writes:
    >
    > > Considering this case in find_free_channels():
    > >
    > > bitmap:
    > > +------------------+-+-+-+-+-+-+-+-+-+-+
    > > | ...... |0|0|0|0|0|0|0|1|0|0|
    > > +------------------+-+-+-+-+-+-+-+-+-+-+
    > >
    > > 1. Channel #2 has been occupied, so bit #2 is 1, and the others
    > > are all 0.
    > > 2. Another thread tries to find 4 free channels from #0.
    > > 3. In the 1st loop, pos starts from 0, and then it checks if the
    > > following 4 bits are all 0, but fails, as bit#2 is 1.
    > > 4. In the 2st loop, pos is not updated, and still starts from 0,
    > > so nothing changes against loop #1.
    > > 5. Dead loop ...
    > >
    > > This patch is to update the pos in step #3 to avoid the issue.
    >
    > The description is slightly confusing, but the patch looks correct and
    > the original code is clearly wrong. Thank you for finding this!
    >
    > Basically, if you request 1 channel 3 times, release the first two and
    > then request 4 channels, you'll be stuck, right?

    Yes, you are right.
    But the real case that I reproduced the issue is a little different:
    I have 2 stp-policy:
    "console": masters "256 259" channels "7 10"
    "user" : masters "256 1024" channels "0 127"
    I understand the policies should not be overlapped, which is caused by some
    other issues.
    So if someone uses "console" to request a channel (who will get Channel #7)
    and then another uses "user" to request more than 8 channels, it will be stuck.
    The commit message is what I trying to abstract the above case, sorry for the
    confusion.

    >
    > Thanks,
    > --
    > Alex

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