svn commit: r254138 - in head: share/man/man9 sys/amd64/amd64 sys/arm/arm sys/cddl/contrib/opensolaris/uts/common/fs/zfs sys/dev/agp sys/dev/drm2/i915 sys/dev/drm2/ttm sys/dev/md sys/fs/fuse sys/fs...

[Attilio Rao]

On Tue, Aug 13, 2013 at 4:22 PM, Ulrich Spörlein <uqs at freebsd.org> wrote:
> On Fri, 2013-08-09 at 11:11:12 +0000, Attilio Rao wrote:
>> Author: attilio
>> Date: Fri Aug  9 11:11:11 2013
>> New Revision: 254138
>> URL: http://svnweb.freebsd.org/changeset/base/254138
>>
>> Log:
>>   The soft and hard busy mechanism rely on the vm object lock to work.
>>   Unify the 2 concept into a real, minimal, sxlock where the shared
>>   acquisition represent the soft busy and the exclusive acquisition
>>   represent the hard busy.
>>   The old VPO_WANTED mechanism becames the hard-path for this new lock
>>   and it becomes per-page rather than per-object.
>>   The vm_object lock becames an interlock for this functionality:
>>   it can be held in both read or write mode.
>>   However, if the vm_object lock is held in read mode while acquiring
>>   or releasing the busy state, the thread owner cannot make any
>>   assumption on the busy state unless it is also busying it.
>>
>>   Also:
>>   - Add a new flag to directly shared busy pages while vm_page_alloc
>>     and vm_page_grab are being executed.  This will be very helpful
>>     once these functions happen under a read object lock.
>>   - Move the swapping sleep into its own per-object flag
>>
>>   The KPI is heavilly changed this is why the version is bumped.
>>   It is very likely that some VM ports users will need to change
>>   their own code.
>>
>>   Sponsored by:       EMC / Isilon storage division
>>   Discussed with:     alc
>>   Reviewed by:        jeff, kib
>>   Tested by:  gavin, bapt (older version)
>>   Tested by:  pho, scottl
>
> The changes to sys/vm/vm_fault.c introduce a call to
> vm_page_sleep_if_busy() where the return code is not checked. The other
> 5 places in the tree check the return code, please fix this here too.
> It's CID 1062398, and I would encourage folks to get an account with
> scan.coverity.com and have an eye on newly found defects.

Not true.
The same call existed also before with exactly the same semantic.
The trick there is that it is not important to check for the return
value because we are going to retry the operation anyway.
The code looks ok to me.

Attilio


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