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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Mar 2021 10:37:54.2436 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 84fa74d3-a6c8-40a1-8f98-08d8eeb0e1cf X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: AM5EUR03FT026.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR08MB2966 > On 23 Mar 2021, at 19:26, Julien Grall wrote: >=20 >=20 >=20 > On 23/03/2021 17:06, Luca Fancellu wrote: >> Hi all, >=20 > Hi, >=20 > Please avoid top posting when answering to a comment. This makes more dif= ficult to follow. >=20 >> I have an update, changing the lock introduced by the serie from spinloc= k_t to raw_spinlock_t, changing the lock/unlock function to use the raw_* v= ersion and keeping the BUG_ON(=E2=80=A6) (now we can because raw_* implemen= tation disable interrupts on preempt_rt) the kernel is booting correctly. >> So seems that the BUG_ON(=E2=80=A6) is needed and the unmask function sh= ould run with interrupt disabled, anyone knows why this change worked? >=20 > Do you mean why no-one spotted the issue before? If so, AFAIK, on vanilla= Linux, spin_lock is still just a wrapper to raw_spinlock. IOW there is no = option to replace it with a RT spinlock. >=20 > So if you don't apply the RT patches, you would not be able to trigger th= e issue. >=20 > As to the fix itself, I think using raw_spinlock_t is the correct thing t= o do because the lock is also used in interrupt context (even with RT enabl= ed). >=20 > Would you be able to send a patch? Yes I=E2=80=99ll send a patch soon >=20 >>> On 23 Mar 2021, at 15:39, Luca Fancellu wrote: >>>=20 >>> Hi Jason, >>>=20 >>> Thanks for your hints, unfortunately seems not an init problem because = in the same init configuration I tried the 5.10.23 (preempt_rt) without the= Juergen patch but with the BUG_ON removed and it boots without problem. So= seems that applying the serie does something (on a preempt_rt kernel) and = we are trying to figure out what. >>>=20 >>>=20 >>>> On 23 Mar 2021, at 12:36, Jason Andryuk wrote: >>>>=20 >>>> On Mon, Mar 22, 2021 at 3:09 PM Luca Fancellu = wrote: >>>>>=20 >>>>> Hi Juergen, >>>>>=20 >>>>> Yes you are right it was my mistake, as you said to remove the BUG_ON= (=E2=80=A6) this serie (https://patchwork.kernel.org/project/xen-devel/cove= r/20210306161833.4552-1-jgross@suse.com/) is needed, since I=E2=80=99m usin= g yocto I=E2=80=99m able to build a preempt_rt kernel up to the 5.10.23 and= for this reason I=E2=80=99m applying that serie on top of this version, th= en I=E2=80=99m removing the BUG_ON(=E2=80=A6). >>>>>=20 >>>>> A thing that was not expected is that now the Dom0 kernel is stuck on= =E2=80=9CSetting domain 0 name, domid and JSON config=E2=80=A6=E2=80=9D st= ep and the system seems unresponsive. Seems like a deadlock issue but looki= ng into the serie we can=E2=80=99t spot anything and that serie was also te= sted by others from the community. >=20 > The deadlock is expected. When you enable RT spinlock, the interrupts wil= l not disabled even when you call spin_lock_irqsave(). >=20 > As the lock is also used in interrupt context (e.g. with interrupt masked= ), this will lead to a deadlock because the lock can be held with interrupt= unmasked. >=20 > This is quite a common error as developpers are not yet used to test RT. = I remember finding a few other instances like that when I worked on RT a co= uple of years ago. >=20 > For future reference, I think CONFIG_PROVE_LOCKING=3Dy could help you to = detect (potential) deadlock. >=20 > Cheers, >=20 > --=20 > Julien Grall