2023-06-28 09:24:12

by Suren Baghdasaryan

Subject: [PATCH v4 3/6] mm: drop per-VMA lock when returning VM_FAULT_RETRY or VM_FAULT_COMPLETED

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 when returning
VM_FAULT_RETRY or VM_FAULT_COMPLETED. Currently the only path returning
VM_FAULT_RETRY under per-VMA locks is do_swap_page and no path returns
VM_FAULT_COMPLETED for now.

Signed-off-by: Suren Baghdasaryan <[email protected]>
---
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 | 1 +
5 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c85b6d70b222..9c06c53a9ff3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -612,7 +612,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
goto lock_mmap;
}
fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, 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, unsigned long address,
}

fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, 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_regs *regs, int access)
goto lock_mmap;
}
fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, 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 = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, 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..f14d45957b83 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3713,6 +3713,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)

if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
ret = VM_FAULT_RETRY;
+ vma_end_read(vma);
goto out;
}

--
2.41.0.162.gfafddb0af9-goog

2023-06-28 13:54:07

by Peter Xu

Subject: Re: [PATCH v4 3/6] mm: drop per-VMA lock when returning VM_FAULT_RETRY or VM_FAULT_COMPLETED

On Wed, Jun 28, 2023 at 12:17:57AM -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 when returning
> VM_FAULT_RETRY or VM_FAULT_COMPLETED. Currently the only path returning
> VM_FAULT_RETRY under per-VMA locks is do_swap_page and no path returns
> VM_FAULT_COMPLETED for now.
>
> Signed-off-by: Suren Baghdasaryan <[email protected]>

Acked-by: Peter Xu <[email protected]>

--
Peter Xu