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Fri, 27 Jan 2023 11:42:18 -0800 (PST) Date: Fri, 27 Jan 2023 11:41:04 -0800 In-Reply-To: <20230127194110.533103-1-surenb@google.com> Mime-Version: 1.0 References: <20230127194110.533103-1-surenb@google.com> X-Mailer: git-send-email 2.39.1.456.gfc5497dd1b-goog Message-ID: <20230127194110.533103-28-surenb@google.com> Subject: [PATCH v2 27/33] mm: prevent userfaults to be handled under per-vma lock From: Suren Baghdasaryan To: akpm@linux-foundation.org X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: michel@lespinasse.org, joelaf@google.com, songliubraving@fb.com, mhocko@suse.com, leewalsh@google.com, david@redhat.com, peterz@infradead.org, bigeasy@linutronix.de, peterx@redhat.com, dhowells@redhat.com, linux-mm@kvack.org, edumazet@google.com, jglisse@google.com, punit.agrawal@bytedance.com, will@kernel.org, arjunroy@google.com, dave@stgolabs.net, minchan@google.com, x86@kernel.org, hughd@google.com, willy@infradead.org, gurua@google.com, mingo@redhat.com, linux-arm-kernel@lists.infradead.org, rientjes@google.com, axelrasmussen@google.com, kernel-team@android.com, soheil@google.com, paulmck@kernel.org, jannh@google.com, liam.howlett@oracle.com, shakeelb@google.com, luto@kernel.org, gthelen@google.com, ldufour@linux.ibm.com, surenb@google.com, vbabka@suse.cz, posk@google.com, lstoakes@gmail.com, peterjung1337@gmail.com, linuxppc-dev@lists.ozlabs.org, kent.overstreet@linux.dev, linux-kernel@vger.kernel.org, hannes@cmpxchg.org, tatashin@google.com, mgorman@techsingularity.net, rp pt@kernel.org Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Due to the possibility of handle_userfault dropping mmap_lock, avoid fault handling under VMA lock and retry holding mmap_lock. This can be handled more gracefully in the future. Signed-off-by: Suren Baghdasaryan Suggested-by: Peter Xu --- mm/memory.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 33ecc850d3cb..55582c6fa2fd 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5256,6 +5256,15 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, if (!vma_start_read(vma)) goto inval; + /* + * Due to the possibility of userfault handler dropping mmap_lock, avoid + * it for now and fall back to page fault handling under mmap_lock. + */ + if (userfaultfd_armed(vma)) { + vma_end_read(vma); + goto inval; + } + /* Check since vm_start/vm_end might change before we lock the VMA */ if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { vma_end_read(vma);