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Message-ID: <20241107040239.2847143-3-cmllamas@google.com>
Date: Thu, 7 Nov 2024 04:02:24 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Arve Hjønnevåg" <arve@...roid.com>, Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>,
Joel Fernandes <joel@...lfernandes.org>, Christian Brauner <brauner@...nel.org>,
Carlos Llamas <cmllamas@...gle.com>, Suren Baghdasaryan <surenb@...gle.com>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
David Hildenbrand <david@...hat.com>, Barry Song <v-songbaohua@...o.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH v2 2/8] binder: concurrent page installation
Allow multiple callers to install pages simultaneously by downgrading
the mmap_sem to non-exclusive mode. Races to the same PTE are handled
using get_user_pages_remote() to retrieve the already installed page.
This method significantly reduces contention in the mmap semaphore.
To ensure safety, vma_lookup() is used (instead of alloc->vma) to avoid
operating on an isolated VMA. In addition, zap_page_range_single() is
called under the alloc->mutex to avoid racing with the shrinker.
Many thanks to Barry Song who posted a similar approach [1].
Link: https://lore.kernel.org/all/20240902225009.34576-1-21cnbao@gmail.com/ [1]
Cc: David Hildenbrand <david@...hat.com>
Cc: Barry Song <v-songbaohua@...o.com>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Liam R. Howlett <Liam.Howlett@...cle.com>
Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
---
drivers/android/binder_alloc.c | 64 +++++++++++++++++++++-------------
1 file changed, 40 insertions(+), 24 deletions(-)
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 7241bf4a3ff2..acdc05552603 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -221,26 +221,14 @@ static int binder_install_single_page(struct binder_alloc *alloc,
struct binder_lru_page *lru_page,
unsigned long addr)
{
+ struct vm_area_struct *vma;
struct page *page;
- int ret = 0;
+ long npages;
+ int ret;
if (!mmget_not_zero(alloc->mm))
return -ESRCH;
- /*
- * Protected with mmap_sem in write mode as multiple tasks
- * might race to install the same page.
- */
- mmap_write_lock(alloc->mm);
- if (binder_get_installed_page(lru_page))
- goto out;
-
- if (!alloc->vma) {
- pr_err("%d: %s failed, no vma\n", alloc->pid, __func__);
- ret = -ESRCH;
- goto out;
- }
-
page = alloc_page(GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO);
if (!page) {
pr_err("%d: failed to allocate page\n", alloc->pid);
@@ -248,19 +236,47 @@ static int binder_install_single_page(struct binder_alloc *alloc,
goto out;
}
- ret = vm_insert_page(alloc->vma, addr, page);
- if (ret) {
- pr_err("%d: %s failed to insert page at offset %lx with %d\n",
- alloc->pid, __func__, addr - alloc->buffer, ret);
+ mmap_read_lock(alloc->mm);
+ vma = vma_lookup(alloc->mm, addr);
+ if (!vma || vma != alloc->vma) {
+ mmap_read_unlock(alloc->mm);
__free_page(page);
- ret = -ENOMEM;
+ pr_err("%d: %s failed, no vma\n", alloc->pid, __func__);
+ ret = -ESRCH;
goto out;
}
- /* Mark page installation complete and safe to use */
- binder_set_installed_page(lru_page, page);
+ ret = vm_insert_page(vma, addr, page);
+ switch (ret) {
+ case -EBUSY:
+ /*
+ * EBUSY is ok. Someone installed the pte first but the
+ * lru_page->page_ptr has not been updated yet. Discard
+ * our page and look up the one already installed.
+ */
+ ret = 0;
+ __free_page(page);
+ npages = get_user_pages_remote(alloc->mm, addr, 1, 0, &page, NULL);
+ if (npages <= 0) {
+ pr_err("%d: failed to find page at offset %lx\n",
+ alloc->pid, addr - alloc->buffer);
+ ret = -ESRCH;
+ break;
+ }
+ fallthrough;
+ case 0:
+ /* Mark page installation complete and safe to use */
+ binder_set_installed_page(lru_page, page);
+ break;
+ default:
+ __free_page(page);
+ pr_err("%d: %s failed to insert page at offset %lx with %d\n",
+ alloc->pid, __func__, addr - alloc->buffer, ret);
+ ret = -ENOMEM;
+ break;
+ }
+ mmap_read_unlock(alloc->mm);
out:
- mmap_write_unlock(alloc->mm);
mmput_async(alloc->mm);
return ret;
}
@@ -1091,7 +1107,6 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
trace_binder_unmap_kernel_end(alloc, index);
list_lru_isolate(lru, item);
- mutex_unlock(&alloc->mutex);
spin_unlock(lock);
if (vma) {
@@ -1102,6 +1117,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
trace_binder_unmap_user_end(alloc, index);
}
+ mutex_unlock(&alloc->mutex);
mmap_read_unlock(mm);
mmput_async(mm);
__free_page(page_to_free);
--
2.47.0.199.ga7371fff76-goog
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