[PATCH v3] mm: Downgrade mmap_sem before locking or populating on mmap
From: Andy Lutomirski
Date: Mon Dec 17 2012 - 20:27:46 EST
This is a serious cause of mmap_sem contention. MAP_POPULATE
and MCL_FUTURE, in particular, are disastrous in multithreaded programs.
This is not a complete solution due to reader/writer fairness.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
Changes from v2:
The mmap functions now unconditionally downgrade mmap_sem. This is
slightly slower but a lot simpler.
Changes from v1:
The non-unlocking versions of do_mmap_pgoff and mmap_region are still
available for aio_setup_ring's benefit. In theory, aio_setup_ring
would do better with a lock-downgrading version, but that would be
somewhat ugly and doesn't help my workload.
arch/tile/mm/elf.c | 11 +++--
fs/aio.c | 11 ++---
include/linux/mm.h | 15 +++++--
ipc/shm.c | 8 +++-
mm/fremap.c | 9 +++-
mm/mmap.c | 122 ++++++++++++++++++++++++++++++++++++-----------------
mm/util.c | 5 ++-
7 files changed, 123 insertions(+), 58 deletions(-)
diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
index 3cfa98b..313acb2 100644
--- a/arch/tile/mm/elf.c
+++ b/arch/tile/mm/elf.c
@@ -129,12 +129,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
*/
if (!retval) {
unsigned long addr = MEM_USER_INTRPT;
- addr = mmap_region(NULL, addr, INTRPT_SIZE,
- MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
- VM_READ|VM_EXEC|
- VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0);
+ addr = mmap_region_downgrade_write(
+ NULL, addr, INTRPT_SIZE,
+ MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
+ VM_READ|VM_EXEC|
+ VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0);
+ up_read(&mm->mmap-sem);
if (addr > (unsigned long) -PAGE_SIZE)
retval = (int) addr;
+ return retval; /* We already unlocked mmap_sem. */
}
#endif
diff --git a/fs/aio.c b/fs/aio.c
index 71f613c..912d3d8 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -127,11 +127,12 @@ static int aio_setup_ring(struct kioctx *ctx)
info->mmap_size = nr_pages * PAGE_SIZE;
dprintk("attempting mmap of %lu bytes\n", info->mmap_size);
down_write(&ctx->mm->mmap_sem);
- info->mmap_base = do_mmap_pgoff(NULL, 0, info->mmap_size,
- PROT_READ|PROT_WRITE,
- MAP_ANONYMOUS|MAP_PRIVATE, 0);
+ info->mmap_base = do_mmap_pgoff_downgrade_write(
+ NULL, 0, info->mmap_size,
+ PROT_READ|PROT_WRITE,
+ MAP_ANONYMOUS|MAP_PRIVATE, 0);
if (IS_ERR((void *)info->mmap_base)) {
- up_write(&ctx->mm->mmap_sem);
+ up_read(&ctx->mm->mmap_sem);
info->mmap_size = 0;
aio_free_ring(ctx);
return -EAGAIN;
@@ -141,7 +142,7 @@ static int aio_setup_ring(struct kioctx *ctx)
info->nr_pages = get_user_pages(current, ctx->mm,
info->mmap_base, nr_pages,
1, 0, info->ring_pages, NULL);
- up_write(&ctx->mm->mmap_sem);
+ up_read(&ctx->mm->mmap_sem);
if (unlikely(info->nr_pages != nr_pages)) {
aio_free_ring(ctx);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bcaab4e..a44aa00 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1441,12 +1441,19 @@ extern int install_special_mapping(struct mm_struct *mm,
extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
-extern unsigned long mmap_region(struct file *file, unsigned long addr,
+/*
+ * These functions are called with mmap_sem held for write and they return
+ * with mmap_sem held for read.
+ */
+extern unsigned long mmap_region_downgrade_write(
+ struct file *file, unsigned long addr,
unsigned long len, unsigned long flags,
vm_flags_t vm_flags, unsigned long pgoff);
-extern unsigned long do_mmap_pgoff(struct file *, unsigned long,
- unsigned long, unsigned long,
- unsigned long, unsigned long);
+extern unsigned long do_mmap_pgoff_downgrade_write(
+ struct file *, unsigned long addr,
+ unsigned long len, unsigned long prot,
+ unsigned long flags, unsigned long pgoff);
+
extern int do_munmap(struct mm_struct *, unsigned long, size_t);
/* These take the mm semaphore themselves */
diff --git a/ipc/shm.c b/ipc/shm.c
index dff40c9..482f3d6 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1068,12 +1068,16 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
addr > current->mm->start_stack - size - PAGE_SIZE * 5)
goto invalid;
}
-
- user_addr = do_mmap_pgoff(file, addr, size, prot, flags, 0);
+
+ user_addr = do_mmap_pgoff_downgrade_write(file, addr, size,
+ prot, flags, 0);
+ up_read(¤t->mm->mmap_sem);
*raddr = user_addr;
err = 0;
if (IS_ERR_VALUE(user_addr))
err = (long)user_addr;
+ goto out_fput;
+
invalid:
up_write(¤t->mm->mmap_sem);
diff --git a/mm/fremap.c b/mm/fremap.c
index a0aaf0e..55c4a9b 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -200,8 +200,9 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
struct file *file = get_file(vma->vm_file);
flags &= MAP_NONBLOCK;
- addr = mmap_region(file, start, size,
- flags, vma->vm_flags, pgoff);
+ addr = mmap_region_downgrade_write(
+ file, start, size, flags, vma->vm_flags, pgoff);
+ has_write_lock = 0;
fput(file);
if (IS_ERR_VALUE(addr)) {
err = addr;
@@ -237,6 +238,10 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
/*
* might be mapping previously unmapped range of file
*/
+ if (unlikely(has_write_lock)) {
+ downgrade_write(&mm->mmap_sem);
+ has_write_lock = 0;
+ }
mlock_vma_pages_range(vma, start, start + size);
} else {
if (unlikely(has_write_lock)) {
diff --git a/mm/mmap.c b/mm/mmap.c
index 9a796c4..3913262 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -999,9 +999,10 @@ static inline unsigned long round_hint_to_min(unsigned long hint)
* The caller must hold down_write(¤t->mm->mmap_sem).
*/
-unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
- unsigned long len, unsigned long prot,
- unsigned long flags, unsigned long pgoff)
+unsigned long do_mmap_pgoff_downgrade_write(
+ struct file *file, unsigned long addr,
+ unsigned long len, unsigned long prot,
+ unsigned long flags, unsigned long pgoff)
{
struct mm_struct * mm = current->mm;
struct inode *inode;
@@ -1017,31 +1018,39 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
if (!(file && (file->f_path.mnt->mnt_flags & MNT_NOEXEC)))
prot |= PROT_EXEC;
- if (!len)
- return -EINVAL;
+ if (!len) {
+ addr = -EINVAL;
+ goto out_downgrade;
+ }
if (!(flags & MAP_FIXED))
addr = round_hint_to_min(addr);
/* Careful about overflows.. */
len = PAGE_ALIGN(len);
- if (!len)
- return -ENOMEM;
+ if (!len) {
+ addr = -ENOMEM;
+ goto out_downgrade;
+ }
/* offset overflow? */
- if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
- return -EOVERFLOW;
+ if ((pgoff + (len >> PAGE_SHIFT)) < pgoff) {
+ addr = -EOVERFLOW;
+ goto out_downgrade;
+ }
/* Too many mappings? */
- if (mm->map_count > sysctl_max_map_count)
- return -ENOMEM;
+ if (mm->map_count > sysctl_max_map_count) {
+ addr = -ENOMEM;
+ goto out_downgrade;
+ }
/* Obtain the address to map to. we verify (or select) it and ensure
* that it represents a valid section of the address space.
*/
addr = get_unmapped_area(file, addr, len, pgoff, flags);
if (addr & ~PAGE_MASK)
- return addr;
+ goto out_downgrade;
/* Do simple checking here so the lower-level routines won't have
* to. we assume access permissions have been handled by the open
@@ -1050,9 +1059,12 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
vm_flags = calc_vm_prot_bits(prot) | calc_vm_flag_bits(flags) |
mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
- if (flags & MAP_LOCKED)
- if (!can_do_mlock())
- return -EPERM;
+ if (flags & MAP_LOCKED) {
+ if (!can_do_mlock()) {
+ addr = -EPERM;
+ goto out_downgrade;
+ }
+ }
/* mlock MCL_FUTURE? */
if (vm_flags & VM_LOCKED) {
@@ -1061,8 +1073,10 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
locked += mm->locked_vm;
lock_limit = rlimit(RLIMIT_MEMLOCK);
lock_limit >>= PAGE_SHIFT;
- if (locked > lock_limit && !capable(CAP_IPC_LOCK))
- return -EAGAIN;
+ if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
+ addr = -EAGAIN;
+ goto out_downgrade;
+ }
}
inode = file ? file->f_path.dentry->d_inode : NULL;
@@ -1070,21 +1084,27 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
if (file) {
switch (flags & MAP_TYPE) {
case MAP_SHARED:
- if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE))
- return -EACCES;
+ if ((prot&PROT_WRITE) && !(file->f_mode&FMODE_WRITE)) {
+ addr = -EACCES;
+ goto out_downgrade;
+ }
/*
* Make sure we don't allow writing to an append-only
* file..
*/
- if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
- return -EACCES;
+ if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE)) {
+ addr = -EACCES;
+ goto out_downgrade;
+ }
/*
* Make sure there are no mandatory locks on the file.
*/
- if (locks_verify_locked(inode))
- return -EAGAIN;
+ if (locks_verify_locked(inode)) {
+ addr = -EAGAIN;
+ goto out_downgrade;
+ }
vm_flags |= VM_SHARED | VM_MAYSHARE;
if (!(file->f_mode & FMODE_WRITE))
@@ -1092,20 +1112,27 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
/* fall through */
case MAP_PRIVATE:
- if (!(file->f_mode & FMODE_READ))
- return -EACCES;
+ if (!(file->f_mode & FMODE_READ)) {
+ addr = -EACCES;
+ goto out_downgrade;
+ }
if (file->f_path.mnt->mnt_flags & MNT_NOEXEC) {
- if (vm_flags & VM_EXEC)
- return -EPERM;
+ if (vm_flags & VM_EXEC) {
+ addr = -EPERM;
+ goto out_downgrade;
+ }
vm_flags &= ~VM_MAYEXEC;
}
- if (!file->f_op || !file->f_op->mmap)
- return -ENODEV;
+ if (!file->f_op || !file->f_op->mmap) {
+ addr = -ENODEV;
+ goto out_downgrade;
+ }
break;
default:
- return -EINVAL;
+ addr = -EINVAL;
+ goto out_downgrade;
}
} else {
switch (flags & MAP_TYPE) {
@@ -1123,11 +1150,17 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
pgoff = addr >> PAGE_SHIFT;
break;
default:
- return -EINVAL;
+ addr = -EINVAL;
+ goto out_downgrade;
}
}
- return mmap_region(file, addr, len, flags, vm_flags, pgoff);
+ return mmap_region_downgrade_write(file, addr, len,
+ flags, vm_flags, pgoff);
+
+out_downgrade:
+ downgrade_write(&mm->mmap_sem);
+ return addr;
}
SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
@@ -1240,9 +1273,10 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
}
-unsigned long mmap_region(struct file *file, unsigned long addr,
- unsigned long len, unsigned long flags,
- vm_flags_t vm_flags, unsigned long pgoff)
+unsigned long mmap_region_downgrade_write(
+ struct file *file, unsigned long addr,
+ unsigned long len, unsigned long flags,
+ vm_flags_t vm_flags, unsigned long pgoff)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma, *prev;
@@ -1262,8 +1296,10 @@ munmap_back:
}
/* Check against address space limit. */
- if (!may_expand_vm(mm, len >> PAGE_SHIFT))
- return -ENOMEM;
+ if (!may_expand_vm(mm, len >> PAGE_SHIFT)) {
+ error = -ENOMEM;
+ goto unacct_error;
+ }
/*
* Set 'VM_NORESERVE' if we should not account for the
@@ -1284,8 +1320,10 @@ munmap_back:
*/
if (accountable_mapping(file, vm_flags)) {
charged = len >> PAGE_SHIFT;
- if (security_vm_enough_memory_mm(mm, charged))
- return -ENOMEM;
+ if (security_vm_enough_memory_mm(mm, charged)) {
+ error = -ENOMEM;
+ goto unacct_error;
+ }
vm_flags |= VM_ACCOUNT;
}
@@ -1369,9 +1407,12 @@ munmap_back:
if (correct_wcount)
atomic_inc(&inode->i_writecount);
out:
+ downgrade_write(&mm->mmap_sem);
+
perf_event_mmap(vma);
vm_stat_account(mm, vm_flags, file, len >> PAGE_SHIFT);
+
if (vm_flags & VM_LOCKED) {
if (!mlock_vma_pages_range(vma, addr, addr + len))
mm->locked_vm += (len >> PAGE_SHIFT);
@@ -1397,6 +1438,9 @@ free_vma:
unacct_error:
if (charged)
vm_unacct_memory(charged);
+
+ downgrade_write(&mm->mmap_sem);
+
return error;
}
diff --git a/mm/util.c b/mm/util.c
index dc3036c..ab489a7 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -359,8 +359,9 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
ret = security_mmap_file(file, prot, flag);
if (!ret) {
down_write(&mm->mmap_sem);
- ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff);
- up_write(&mm->mmap_sem);
+ ret = do_mmap_pgoff_downgrade_write(
+ file, addr, len, prot, flag, pgoff);
+ up_read(&mm->mmap_sem);
}
return ret;
}
--
1.7.11.7
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