b6366b15a2
commit dae55b6fef58530c13df074bcc182c096609339e upstream.
Immediate retry of EQBS after CCQ 96 means that we potentially misreport
the state of buffers inspected during the first EQBS call.
This occurs when
1. the first EQBS finds all inspected buffers still in the initial state
set by the driver (ie INPUT EMPTY or OUTPUT PRIMED),
2. the EQBS terminates early with CCQ 96, and
3. by the time that the second EQBS comes around, the state of those
previously inspected buffers has changed.
If the state reported by the second EQBS is 'driver-owned', all we know
is that the previous buffers are driver-owned now as well. But we can't
tell if they all have the same state. So for instance
- the second EQBS reports OUTPUT EMPTY, but any number of the previous
buffers could be OUTPUT ERROR by now,
- the second EQBS reports OUTPUT ERROR, but any number of the previous
buffers could be OUTPUT EMPTY by now.
Effectively, this can result in both over- and underreporting of errors.
If the state reported by the second EQBS is 'HW-owned', that doesn't
guarantee that the previous buffers have not been switched to
driver-owned in the mean time. So for instance
- the second EQBS reports INPUT EMPTY, but any number of the previous
buffers could be INPUT PRIMED (or INPUT ERROR) by now.
This would result in failure to process pending work on the queue. If
it's the final check before yielding initiative, this can cause
a (temporary) queue stall due to IRQ avoidance.
Fixes: 25f269f17316 ("[S390] qdio: EQBS retry after CCQ 96")
Cc: <stable@vger.kernel.org> #v3.2+
Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.