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CH3PR10MB7329.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Oct 2025 00:00:48.8436 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 2bbsi7ymlJ8xkPKTs1MJkn7PsqA4EN5IORtt8PRTDGCCyytiyT9I9+6sv01awCTO6V7cqndv6//Xp4kkPB9u9Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR10MB7205 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-23_03,2025-10-22_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 spamscore=0 mlxscore=0 phishscore=0 suspectscore=0 malwarescore=0 bulkscore=0 mlxlogscore=818 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2510020000 definitions=main-2510230218 X-Proofpoint-GUID: AuTcGGNbwSduG2posjU2Bq0bUP_RF68k X-Authority-Analysis: v=2.4 cv=bLgb4f+Z c=1 sm=1 tr=0 ts=68fac1b5 b=1 cx=c_pps a=qoll8+KPOyaMroiJ2sR5sw==:117 a=qoll8+KPOyaMroiJ2sR5sw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=x6icFKpwvdMA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=bC-a23v3AAAA:8 a=_DkvylGvobcdNYOqZXIA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=FO4_E8m0qiDe52t0p3_H:22 cc=ntf awl=host:12092 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDIyMDA3MSBTYWx0ZWRfX0sJmym+FJ9Ti zNQs24LBL/vVonL67s4SBE/rpDEkUaOO/6PfGVHuQS+GAuzm9XIdZcEhF2jmhntfamv+pCwuTcT NcLqmAPvTFK72a0Lfo6+fQwosZzVFvoSypwH2EMlUSfnrj8/MY81A3Jb4AoAJQjJqg65zeYxYv9 Ey34/4lHP4ShEZdJjOIyOahWrW8MMbx9MZiJlEkExzkaL/szbrAGr5GP6si99/4Fzko1TmqxrMn LpajNLb8PVPDYpDGnTRsu/V6AcTZrulei7AigAheNO8ay6DoUDkx8xTYw3FkNGd4z/oAuWeyeLu GkJ1gqv/+dgphLt3qtaosZerXlsuTVT78zRB53io7mSzHEempsTNb7VH7QjTbYeQLJvvASN6XUx 6ytln/Cgoo2DhQbSayf6pDflCmC9v/CvaFJLQRG/dXHhJDgf3EA= X-Proofpoint-ORIG-GUID: AuTcGGNbwSduG2posjU2Bq0bUP_RF68k On Thu, Oct 23, 2025 at 04:13:37PM -0700, Alexei Starovoitov wrote: > On Thu, Oct 23, 2025 at 5:01 AM Vlastimil Babka wrote: > > > > Since commit af92793e52c3 ("slab: Introduce kmalloc_nolock() and > > kfree_nolock().") there's a possibility in alloc_single_from_new_slab() > > that we discard the newly allocated slab if we can't spin and we fail to > > trylock. As a result we don't perform inc_slabs_node() later in the > > function. Instead we perform a deferred deactivate_slab() which can > > either put the unacounted slab on partial list, or discard it > > immediately while performing dec_slabs_node(). Either way will cause an > > accounting imbalance. > > > > Fix this by not marking the slab as frozen, and using free_slab() > > instead of deactivate_slab() for non-frozen slabs in > > free_deferred_objects(). For CONFIG_SLUB_TINY, that's the only possible > > case. By not using discard_slab() we avoid dec_slabs_node(). > > > > Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") > > Signed-off-by: Vlastimil Babka > > --- > > Changes in v2: > > - Fix the problem differently. Harry pointed out that we can't move > > inc_slabs_node() outside of list_lock protected regions as that would > > reintroduce issues fixed by commit c7323a5ad078 > > - Link to v1: https://patch.msgid.link/20251022-fix-slab-accounting-v1-1-27870ec363ce@suse.cz > > --- > > mm/slub.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/mm/slub.c b/mm/slub.c > > index 23d8f54e9486..87a1d2f9de0d 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -3422,7 +3422,6 @@ static void *alloc_single_from_new_slab(struct kmem_cache *s, struct slab *slab, > > > > if (!allow_spin && !spin_trylock_irqsave(&n->list_lock, flags)) { > > /* Unlucky, discard newly allocated slab */ > > - slab->frozen = 1; > > defer_deactivate_slab(slab, NULL); > > return NULL; > > } > > @@ -6471,9 +6470,12 @@ static void free_deferred_objects(struct irq_work *work) > > struct slab *slab = container_of(pos, struct slab, llnode); > > > > #ifdef CONFIG_SLUB_TINY > > - discard_slab(slab->slab_cache, slab); > > + free_slab(slab->slab_cache, slab); > > #else > > - deactivate_slab(slab->slab_cache, slab, slab->flush_freelist); > > + if (slab->frozen) > > + deactivate_slab(slab->slab_cache, slab, slab->flush_freelist); > > + else > > + free_slab(slab->slab_cache, slab); > > A bit odd to use 'frozen' flag as such a signal. > I guess I'm worried that truly !frozen slab can come here > via ___slab_alloc() -> retry_load_slab: -> defer_deactivate_slab(). > And things will be much worse than just accounting. But the cpu slab must have been frozen before it's attached to c->slab? > Maybe add > inc_slabs_node(s, nid, slab->objects); > right before > defer_deactivate_slab(slab, NULL); > return NULL; > > I don't quite get why c7323a5ad078 is doing everything under n->list_lock. > It's been 3 years since. When n->nr_slabs is inconsistent, validate_slab_node() might report an error (false positive) when someone wrote '1' to /sys/kernel/slab//validate > We have an empty slab here that is going to be freed soon. > It's effectively frozen, so inc_slabs_node() on it seems like a safe fix. -- Cheers, Harry / Hyeonggon