Re: [Xen-devel] xen-unstable (4.14 to be): Assertion '!preempt_count()' failed at preempt.c:36

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

On 04/12/2019 18:30, Jan Beulich wrote:
> On 04.12.2019 18:21, Sander Eikelenboom wrote:
>> On current xen-unstable (4.14 to be) and AMD cpu:
>>
>> After rebooting the host, while the guests are starting, I hit the assertion 
>> below.
>> xen-staging-4.13 seems fine on the same machine.
> 
> Nothing between 4.13 RC4 and the tip of staging stands out,
> so I wonder if you could bisect over this range? Or perhaps
> someone else sees something I don't see (right now).
> 
> Jan

Bisection came up with:

commit cd7dedad8209753e0fc8a97e61d04b74912b53dc
Author: Paul Durrant <paul.durrant@xxxxxxxxxx>
Date:   Fri Nov 15 18:59:30 2019 +0000

    passthrough: simplify locking and logging
    
    Dropping the pcidevs lock between calling device_assigned() and
    assign_device() means that the latter has to do the same check as the
    former for no obvious gain. Also, since long running operations under
    pcidevs lock already drop the lock and return -ERESTART periodically there
    is little point in immediately failing an assignment operation with
    -ERESTART just because the pcidevs lock could not be acquired (for the
    second time, having already blocked on acquiring the lock in
    device_assigned()).
    
    This patch instead acquires the lock once for assignment (or test assign)
    operations directly in iommu_do_pci_domctl() and thus can remove the
    duplicate domain ownership check in assign_device(). Whilst in the
    neighbourhood, the patch also removes some debug logging from
    assign_device() and deassign_device() and replaces it with proper error
    logging, which allows error logging in iommu_do_pci_domctl() to be
    removed.
    
    Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>



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