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X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 5KXKeNNp+kIHE8RrJaIfT2CQYKsHs2cMn6KbW8F6u0NHq/ZNz1U2LrSRCAO1QoXSmkQZdJnKHTgRnojh0ScsF7lHABx73Qx//RYtlk178e8= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR10MB4493 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-01-14_02,2025-01-13_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 mlxscore=0 malwarescore=0 spamscore=0 suspectscore=0 mlxlogscore=768 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2411120000 definitions=main-2501140096 X-Proofpoint-ORIG-GUID: a2it5hqYhlsj3aEwFe1SV5jr7m1TVtsH X-Proofpoint-GUID: a2it5hqYhlsj3aEwFe1SV5jr7m1TVtsH On Mon, Jan 13, 2025 at 12:42:53PM -0800, Suren Baghdasaryan wrote: > On Mon, Jan 13, 2025 at 12:32 PM Vlastimil Babka wrote: > > > > On 1/13/25 20:11, Suren Baghdasaryan wrote: > > > On Mon, Jan 13, 2025 at 9:13 AM Lorenzo Stoakes > > > wrote: > > >> > > >> On Mon, Jan 13, 2025 at 09:02:50AM -0800, Suren Baghdasaryan wrote: > > >> > On Mon, Jan 13, 2025 at 4:05 AM Lorenzo Stoakes > > >> > wrote: > > >> > > > > >> > > On Fri, Jan 10, 2025 at 08:25:52PM -0800, Suren Baghdasaryan wrote: > > >> > > > When exit_mmap() removes vmas belonging to an exiting task, it does not > > >> > > > mark them as detached since they can't be reached by other tasks and they > > >> > > > will be freed shortly. Once we introduce vma reuse, all vmas will have to > > >> > > > be in detached state before they are freed to ensure vma when reused is > > >> > > > in a consistent state. Add missing vma_mark_detached() before freeing the > > >> > > > vma. > > >> > > > > >> > > Hmm this really makes me worry that we'll see bugs from this detached > > >> > > stuff, do we make this assumption anywhere else I wonder? > > >> > > > >> > This is the only place which does not currently detach the vma before > > >> > freeing it. If someone tries adding a case like that in the future, > > >> > they will be met with vma_assert_detached() inside vm_area_free(). > > >> > > >> OK good to know! > > >> > > >> Again, I wonder if we should make these assertions stronger as commented > > >> elsewhere, because if we see them in production isn't that worth an actual > > >> non-debug WARN_ON_ONCE()? > > > > > > Sure. I'll change vma_assert_attached()/vma_assert_detached() to use > > > WARN_ON_ONCE() and to return a bool (see also my reply in the patch > > > [0/17]). > > > > So is this a case of "someone might introduce code later that will violate > > them" as alluded to above? Unconditional WARN_ON_ONCE seems too much then. My concern is that there is a broken case that remains hidden because nothing is actually checked in production, which would then become really difficult to debug should somebody report it. We intend the WARN_ONxxx() functions to be asserting things that -should not be- for precisely this kind of purpose so I think it makes sense here. > > Yes, I wanted to make sure refcounting will not be broken by someone > doing re-attach/re-detach. Yes, and debugging this without it could be really horrible. > > > > > In general it's not easy to determine how paranoid we should be in non-debug > > code, but I'm not sure what's the need here specifically. > > I'm not sure how strict we should be but we definitely should try to > catch refcounting mistakes and that's my goal here. Yes I think it is worth it here (obviously :) > > >