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Tue, 27 Jun 2023 09:25:32 -0700 (PDT) MIME-Version: 1.0 References: <20230627042321.1763765-1-surenb@google.com> <20230627042321.1763765-4-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 27 Jun 2023 09:25:21 -0700 Message-ID: Subject: Re: [PATCH v3 3/8] mm: drop per-VMA lock in handle_mm_fault if retrying or when finished To: Peter Xu Cc: akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, hdanton@sina.com, apopple@nvidia.com, ying.huang@intel.com, david@redhat.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: gneqf4nugtd1pjod9qdejhino5b3n99f X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: F18CAA0020 X-Rspam-User: X-HE-Tag: 1687883133-592086 X-HE-Meta: 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 kpkTNe3x IinmlcgzmUHFPdG1vvlrC0m/1p5GtS3Urm9OxizOcd4HdP/Dq6r6rgvDThHkegKyRjzj8b1pQ8yH80ZVkKW7kjyEDjYnerzAslXxNs/uctUCU5AiFjeqvYd5csORApmLHAlhz5hQGitlemiBaqy5sUmpsPMbWpsOOtO+kFALaTAyfFwysE3i4YEfMV1y8RWj0jma97Rl+T15vTz+Yu3W8OQH+U/0rOgQIdwG3idDwxGYSZDe55dCTglm5volw10bTsPhdqvB5+8offMEbyZeGV13v/ZdJ7K8mjxcqu+UWcGpKrL0sTWD8u4X1i1KRfGWvaTjMj5kai0RszmQ= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jun 27, 2023 at 8:28=E2=80=AFAM Peter Xu wrote: > > On Mon, Jun 26, 2023 at 09:23:16PM -0700, Suren Baghdasaryan wrote: > > handle_mm_fault returning VM_FAULT_RETRY or VM_FAULT_COMPLETED means > > mmap_lock has been released. However with per-VMA locks behavior is > > different and the caller should still release it. To make the > > rules consistent for the caller, drop the per-VMA lock before returning > > from handle_mm_fault when page fault should be retried or is completed. > > > > Signed-off-by: Suren Baghdasaryan > > --- > > arch/arm64/mm/fault.c | 3 ++- > > arch/powerpc/mm/fault.c | 3 ++- > > arch/s390/mm/fault.c | 3 ++- > > arch/x86/mm/fault.c | 3 ++- > > mm/memory.c | 12 +++++++++++- > > 5 files changed, 19 insertions(+), 5 deletions(-) > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > index 6045a5117ac1..89f84e9ea1ff 100644 > > --- a/arch/arm64/mm/fault.c > > +++ b/arch/arm64/mm/fault.c > > @@ -601,7 +601,8 @@ static int __kprobes do_page_fault(unsigned long fa= r, unsigned long esr, > > goto lock_mmap; > > } > > fault =3D handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LO= CK, regs); > > - vma_end_read(vma); > > + if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED))) > > + vma_end_read(vma); > > > > if (!(fault & VM_FAULT_RETRY)) { > > count_vm_vma_lock_event(VMA_LOCK_SUCCESS); > > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > > index 531177a4ee08..4697c5dca31c 100644 > > --- a/arch/powerpc/mm/fault.c > > +++ b/arch/powerpc/mm/fault.c > > @@ -494,7 +494,8 @@ static int ___do_page_fault(struct pt_regs *regs, u= nsigned long address, > > } > > > > fault =3D handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LO= CK, regs); > > - vma_end_read(vma); > > + if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED))) > > + vma_end_read(vma); > > > > if (!(fault & VM_FAULT_RETRY)) { > > count_vm_vma_lock_event(VMA_LOCK_SUCCESS); > > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c > > index b65144c392b0..cccefe41038b 100644 > > --- a/arch/s390/mm/fault.c > > +++ b/arch/s390/mm/fault.c > > @@ -418,7 +418,8 @@ static inline vm_fault_t do_exception(struct pt_reg= s *regs, int access) > > goto lock_mmap; > > } > > fault =3D handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LO= CK, regs); > > - vma_end_read(vma); > > + if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED))) > > + vma_end_read(vma); > > if (!(fault & VM_FAULT_RETRY)) { > > count_vm_vma_lock_event(VMA_LOCK_SUCCESS); > > goto out; > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > > index e4399983c50c..d69c85c1c04e 100644 > > --- a/arch/x86/mm/fault.c > > +++ b/arch/x86/mm/fault.c > > @@ -1347,7 +1347,8 @@ void do_user_addr_fault(struct pt_regs *regs, > > goto lock_mmap; > > } > > fault =3D handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LO= CK, regs); > > - vma_end_read(vma); > > + if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED))) > > + vma_end_read(vma); > > > > if (!(fault & VM_FAULT_RETRY)) { > > count_vm_vma_lock_event(VMA_LOCK_SUCCESS); > > diff --git a/mm/memory.c b/mm/memory.c > > index f69fbc251198..9011ad63c41b 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -5086,7 +5086,17 @@ static vm_fault_t __handle_mm_fault(struct vm_ar= ea_struct *vma, > > } > > } > > > > - return handle_pte_fault(&vmf); > > + ret =3D handle_pte_fault(&vmf); > > + if (ret & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)) { > > + /* > > + * In case of VM_FAULT_RETRY or VM_FAULT_COMPLETED we mig= ht > > + * be still holding per-VMA lock to keep the vma stable a= s long > > + * as possible. Drop it before returning. > > + */ > > + if (vmf.flags & FAULT_FLAG_VMA_LOCK) > > + vma_end_read(vma); > > + } > > This smells hackish.. I'd think better we just release the lock at the > place where we'll return RETRY, and AFAIU swap is the only place vma lock > returns a RETRY with current code base? > > do_swap_page(): > if (vmf->flags & FAULT_FLAG_VMA_LOCK) { > + vma_end_read(vma); > ret =3D VM_FAULT_RETRY; > goto out; > } > > I.e., I don't think VM_FAULT_COMPLETED can even be returned with vma lock > paths yet as it doesn't yet support VM_SHARED. Ack. > > -- > Peter Xu >