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Message-ID: <20230501175025.36233-2-surenb@google.com>
Date: Mon, 1 May 2023 10:50:24 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: akpm@...ux-foundation.org
Cc: willy@...radead.org, hannes@...xchg.org, mhocko@...e.com,
josef@...icpanda.com, jack@...e.cz, ldufour@...ux.ibm.com,
laurent.dufour@...ibm.com, michel@...pinasse.org,
liam.howlett@...cle.com, jglisse@...gle.com, vbabka@...e.cz,
minchan@...gle.com, dave@...olabs.net, punit.agrawal@...edance.com,
lstoakes@...il.com, hdanton@...a.com, apopple@...dia.com,
surenb@...gle.com, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...roid.com
Subject: [PATCH 2/3] mm: drop VMA lock before waiting for migration
migration_entry_wait does not need VMA lock, therefore it can be dropped
before waiting. Introduce VM_FAULT_VMA_UNLOCKED to indicate that VMA
lock was dropped while in handle_mm_fault().
Note that once VMA lock is dropped, the VMA reference can't be used as
there are no guarantees it was not freed.
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
arch/arm64/mm/fault.c | 3 ++-
arch/powerpc/mm/fault.c | 3 ++-
arch/s390/mm/fault.c | 3 ++-
arch/x86/mm/fault.c | 3 ++-
include/linux/mm_types.h | 6 +++++-
mm/memory.c | 12 ++++++++++--
6 files changed, 23 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 9e0db5c387e3..8fa281f49d61 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -602,7 +602,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
}
fault = handle_mm_fault(vma, addr & PAGE_MASK,
mm_flags | FAULT_FLAG_VMA_LOCK, regs);
- vma_end_read(vma);
+ if (!(fault & VM_FAULT_VMA_UNLOCKED))
+ 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..b27730f07141 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_VMA_UNLOCKED))
+ 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..cc923dbb0821 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_VMA_UNLOCKED))
+ 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..ef62ab2fd211 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_VMA_UNLOCKED))
+ vma_end_read(vma);
if (!(fault & VM_FAULT_RETRY)) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 306a3d1a0fa6..b3b57c6da0e1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1030,6 +1030,7 @@ typedef __bitwise unsigned int vm_fault_t;
* fsync() to complete (for synchronous page faults
* in DAX)
* @VM_FAULT_COMPLETED: ->fault completed, meanwhile mmap lock released
+ * @VM_FAULT_VMA_UNLOCKED: VMA lock was released
* @VM_FAULT_HINDEX_MASK: mask HINDEX value
*
*/
@@ -1047,6 +1048,7 @@ enum vm_fault_reason {
VM_FAULT_DONE_COW = (__force vm_fault_t)0x001000,
VM_FAULT_NEEDDSYNC = (__force vm_fault_t)0x002000,
VM_FAULT_COMPLETED = (__force vm_fault_t)0x004000,
+ VM_FAULT_VMA_UNLOCKED = (__force vm_fault_t)0x008000,
VM_FAULT_HINDEX_MASK = (__force vm_fault_t)0x0f0000,
};
@@ -1070,7 +1072,9 @@ enum vm_fault_reason {
{ VM_FAULT_RETRY, "RETRY" }, \
{ VM_FAULT_FALLBACK, "FALLBACK" }, \
{ VM_FAULT_DONE_COW, "DONE_COW" }, \
- { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }
+ { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }, \
+ { VM_FAULT_COMPLETED, "COMPLETED" }, \
+ { VM_FAULT_VMA_UNLOCKED, "VMA_UNLOCKED" }
struct vm_special_mapping {
const char *name; /* The name, e.g. "[vdso]". */
diff --git a/mm/memory.c b/mm/memory.c
index 41f45819a923..8222acf74fd3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3714,8 +3714,16 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
entry = pte_to_swp_entry(vmf->orig_pte);
if (unlikely(non_swap_entry(entry))) {
if (is_migration_entry(entry)) {
- migration_entry_wait(vma->vm_mm, vmf->pmd,
- vmf->address);
+ /* Save mm in case VMA lock is dropped */
+ struct mm_struct *mm = vma->vm_mm;
+
+ if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
+ /* No need to hold VMA lock for migration */
+ vma_end_read(vma);
+ /* CAUTION! VMA can't be used after this */
+ ret |= VM_FAULT_VMA_UNLOCKED;
+ }
+ migration_entry_wait(mm, vmf->pmd, vmf->address);
} else if (is_device_exclusive_entry(entry)) {
vmf->page = pfn_swap_entry_to_page(entry);
ret = remove_device_exclusive_entry(vmf);
--
2.40.1.495.gc816e09b53d-goog
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