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Howlett" , Suren Baghdasaryan , akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, leewalsh@google.com, posk@google.com, michalechner92@googlemail.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 89FAF4000E X-Stat-Signature: dnoaeyxjydu19ebf5176tszo8hsy85jf X-HE-Tag: 1677204390-932862 X-HE-Meta: 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 zRSjTRLD RVXOtgQHSesWFKVcaIhVpVuaCtCRro/EO1TVNATsEteJ5BoQBc2RgcinMB5Bz9wbFlSQ43x3cN2FBECOM6dkCUvVeT2T8fD+y1UcV1FdoEuB82pRIJhm/PPJFBAVPJSGc/K5baOBNzACXbhFA3jAIQU0bCVpCeMC00V0lazZfAtkVnbuiQ96XTtGlrmMGF3SEQuVvuDrkfbjpNfV/ZCl+dODw3R0+L4IsV8Nb36t/qaa1vEGv6d/ncrbmfNVuIt+w1HF2NYPYVT7q9rNwdkr3YEkU6Vl9IOYZQqXM+V6TtgtU2dA/OPjajaeK8ksytbMiGqAIyUdtKX6S37Tj6rMFNroFMpupEAV57UR4vOfIWVfWaiihGfamPPMQO+ETNjN5Pt9rvT34JzmeYpkBYNfCOulhpA== 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 Thu, Feb 23, 2023 at 5:46 PM Liam R. Howlett wrote: > > * Suren Baghdasaryan [230223 16:16]: > > On Thu, Feb 23, 2023 at 12:28 PM Liam R. Howlett > > wrote: > > > > > > > > > Wait, I figured a better place to do this. > > > > > > init_multi_vma_prep() should vma_start_write() on any VMA that is passed > > > in.. that we we catch any modifications here & in vma_merge(), which I > > > think is missed in this patch set? > > > > Hmm. That looks like a good idea but in that case, why not do the > > locking inside vma_prepare() itself? From the description of that > > function it sounds like it was designed to acquire locks before VMA > > modifications, so would be the ideal location for doing that. WDYT? > > That might be even better. I think it will result in even less code. Yes. > > There is also a vma_complete() which might work to call > vma_end_write_all() as well? If there are other VMAs already locked before vma_prepare() then we would unlock them too. Safer to just let mmap_unlock do vma_end_write_all(). > > > The only concern is vma_adjust_trans_huge() being called before > > vma_prepare() but I *think* that's safe because > > vma_adjust_trans_huge() does its modifications after acquiring PTL > > lock, which page fault handlers also have to take. Does that sound > > right? > > I am not sure. We are certainly safe the way it is, and the PTL has to > be safe for concurrent faults.. but this could alter the walk to a page > table while that walk is occurring and I don't think that happens today. > > It might be best to leave the locking order the way you have it, unless > someone can tell us it's safe? Yes, I have the same feelings about changing this. > > We could pass through the three extra variables that are needed to move > the vma_adjust_trans_huge() call within that function as well? This > would have the added benefit of having all locking grouped in the one > location, but the argument list would be getting long, however we could > use the struct. Any issues if I change the order to have vma_prepare() called always before vma_adjust_trans_huge()? That way the VMA will always be locked before vma_adjust_trans_huge() executes and we don't need any additional arguments. > > remove & remove2 should be be detached in vma_prepare() or > vma_complete() as well? They are marked detached in vma_complete() (see https://lore.kernel.org/all/20230216051750.3125598-25-surenb@google.com/) and that should be enough. We should be safe as long as we mark them detached before unlocking the VMA. > > > > > > > > > > > > * Liam R. Howlett [230223 15:20]: > > > > Reviewed-by: Liam R. Howlett > > > > > > > > * Suren Baghdasaryan [230216 00:18]: > > > > > vma_expand and vma_shrink change VMA boundaries. Expansion might also > > > > > result in freeing of an adjacent VMA. Write-lock affected VMAs to prevent > > > > > concurrent page faults. > > > > > > > > > > Signed-off-by: Suren Baghdasaryan > > > > > --- > > > > > mm/mmap.c | 5 +++++ > > > > > 1 file changed, 5 insertions(+) > > > > > > > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > > > > index ec2f8d0af280..f079e5bbcd57 100644 > > > > > --- a/mm/mmap.c > > > > > +++ b/mm/mmap.c > > > > > @@ -674,6 +674,9 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > > > ret = dup_anon_vma(vma, next); > > > > > if (ret) > > > > > return ret; > > > > > + > > > > > + /* Lock the VMA before removing it */ > > > > > + vma_start_write(next); > > > > > } > > > > > > > > > > init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL); > > > > > @@ -686,6 +689,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > > > if (vma_iter_prealloc(vmi)) > > > > > goto nomem; > > > > > > > > > > + vma_start_write(vma); > > > > > vma_adjust_trans_huge(vma, start, end, 0); > > > > > /* VMA iterator points to previous, so set to start if necessary */ > > > > > if (vma_iter_addr(vmi) != start) > > > > > @@ -725,6 +729,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > > > if (vma_iter_prealloc(vmi)) > > > > > return -ENOMEM; > > > > > > > > > > + vma_start_write(vma); > > > > > init_vma_prep(&vp, vma); > > > > > vma_adjust_trans_huge(vma, start, end, 0); > > > > > vma_prepare(&vp); > > > > > -- > > > > > 2.39.1 > > > > > > > > > > > -- > > > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. > > > > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >