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b=sJaBUwGikN9Norhx8A5uvQMDFYl0Mwp8HvEEwLjLgR0wuVFvcc7ERqkxy5ZlLYsDg 0LCAEdD0oTQbmCPM/6MJpOZ1EnAVOzkvmzSr34CThvn+U01XlYliRQ//lSoiqgZDlT Zofky4ajLoqO68zDBfo8dclRZkoicrnAxBT6bOdE= Date: Tue, 31 Mar 2026 14:35:38 -0700 From: Andrew Morton To: "David Hildenbrand (Arm)" Cc: "Lorenzo Stoakes (Oracle)" , Nico Pache , linux-kernel@vger.kernel.org, linux-mm@kvack.org, aarcange@redhat.com, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jackmanb@google.com, jack@suse.cz, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: Re: [PATCH mm-unstable v4 5/5] mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd() Message-Id: <20260331143538.f41a5fef4201a7384388f31c@linux-foundation.org> In-Reply-To: <26fcec86-ee78-4f5c-8ca5-0e6230699cfd@kernel.org> References: <20260325114022.444081-1-npache@redhat.com> <20260325114022.444081-6-npache@redhat.com> <7760c811-e100-4d40-9217-0813c28314be@lucifer.local> <0223d45b-e8b4-49a7-882b-477250d0c14d@kernel.org> <26fcec86-ee78-4f5c-8ca5-0e6230699cfd@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 3276E16000B X-Stat-Signature: q1e3e69jfkwgiysm4mbroxdxmsnatgy1 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1774992942-966645 X-HE-Meta: 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 BhhUh8hF 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 31 Mar 2026 22:00:58 +0200 "David Hildenbrand (Arm)" wrote: > > out_maybelock: > > /* Caller expects us to hold mmap_lock on return */ > > if (mmap_unlocked) { > > *lock_dropped = true; > > mmap_read_lock(mm); > > } > > > > Right. > > The original code used > > bool mmap_locked = true; > > If the fix get squashed, maybe we should revert to that handling to > minimize the churn? > > (this is not in stable, right?) "mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd(): is presently in mm-stable. Doing a big rebase&rework isn't the done thing, I believe. So queue it afterwards, add the Fixes: and tolerate the minor runtime bisection hole. It ends up looking like a later hotfix. Below is what I added to mm-unstable. I added a note-to-self to check in on Nico's question at https://lore.kernel.org/all/CAA1CXcCYLGQBy9nT-MSTPVK=XgWWtD6Af-QiA_6pXtM_2pybPg@mail.gmail.com/T/#u From: "Lorenzo Stoakes (Oracle)" Subject: mm/khugepaged: fix issue with tracking lock Date: Tue, 31 Mar 2026 13:11:18 +0100 We are incorrectly treating lock_dropped to track both whether the lock is currently held and whether or not the lock was ever dropped. Update this change to account for this. Link: https://lkml.kernel.org/r/7760c811-e100-4d40-9217-0813c28314be@lucifer.local Fixes: 330f3758a3bc ("mm/khugepaged: unify khugepaged and madv_collapse with collapse_single_pmd()") Signed-off-by: Lorenzo Stoakes (Oracle) Reviewed-by: Lance Yang Reviewed-by: Nico Pache ... Signed-off-by: Andrew Morton --- mm/khugepaged.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) --- a/mm/khugepaged.c~mm-khugepaged-fix-issue-with-tracking-lock +++ a/mm/khugepaged.c @@ -2828,6 +2828,7 @@ int madvise_collapse(struct vm_area_stru unsigned long hstart, hend, addr; enum scan_result last_fail = SCAN_FAIL; int thps = 0; + bool mmap_unlocked = false; BUG_ON(vma->vm_start > start); BUG_ON(vma->vm_end < end); @@ -2850,10 +2851,11 @@ int madvise_collapse(struct vm_area_stru for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { enum scan_result result = SCAN_FAIL; - if (*lock_dropped) { + if (mmap_unlocked) { cond_resched(); mmap_read_lock(mm); - *lock_dropped = false; + mmap_unlocked = false; + *lock_dropped = true; result = hugepage_vma_revalidate(mm, addr, false, &vma, cc); if (result != SCAN_SUCCEED) { @@ -2864,7 +2866,7 @@ int madvise_collapse(struct vm_area_stru hend = min(hend, vma->vm_end & HPAGE_PMD_MASK); } - result = collapse_single_pmd(addr, vma, lock_dropped, cc); + result = collapse_single_pmd(addr, vma, &mmap_unlocked, cc); switch (result) { case SCAN_SUCCEED: @@ -2893,8 +2895,10 @@ int madvise_collapse(struct vm_area_stru out_maybelock: /* Caller expects us to hold mmap_lock on return */ - if (*lock_dropped) + if (mmap_unlocked) { + *lock_dropped = true; mmap_read_lock(mm); + } out_nolock: mmap_assert_locked(mm); mmdrop(mm); _