[PATCH] mm: Downgrade mmap_sem before locking or populating on mmap
From: Andy Lutomirski
Date: Fri Dec 14 2012 - 00:49:57 EST
This is a serious cause of mmap_sem contention. MAP_POPULATE
and MCL_FUTURE, in particular, are disastrous in multithreaded programs.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
Sensible people use anonymous mappings. I write kernel patches :)
I'm not entirely thrilled by the aesthetics of this patch. The MAP_POPULATE case
could also be improved by doing it without any lock at all. This is still a big
improvement, though.
arch/tile/mm/elf.c | 9 ++--
fs/aio.c | 8 ++--
include/linux/mm.h | 8 ++--
ipc/shm.c | 6 ++-
mm/fremap.c | 10 ++--
mm/mmap.c | 133 +++++++++++++++++++++++++++++++++++++----------------
mm/util.c | 3 +-
7 files changed, 117 insertions(+), 60 deletions(-)
diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
index 3cfa98b..a0441f2 100644
--- a/arch/tile/mm/elf.c
+++ b/arch/tile/mm/elf.c
@@ -129,12 +129,13 @@ 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_unlock(NULL, addr, INTRPT_SIZE,
+ MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE,
+ VM_READ|VM_EXEC|
+ VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC, 0);
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..8e2b162 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -127,11 +127,10 @@ 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_unlock(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);
info->mmap_size = 0;
aio_free_ring(ctx);
return -EAGAIN;
@@ -141,7 +140,6 @@ 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);
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..bb13d11 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1441,12 +1441,12 @@ 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,
+extern unsigned long mmap_region_unlock(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_unlock(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..d0001c8 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1068,12 +1068,14 @@ 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_unlock(file, addr, size, prot, flags, 0);
*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..232402c 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -200,8 +200,8 @@ 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_unlock(file, start, size,
+ flags, vma->vm_flags, pgoff);
fput(file);
if (IS_ERR_VALUE(addr)) {
err = addr;
@@ -209,7 +209,7 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
BUG_ON(addr != start);
err = 0;
}
- goto out;
+ return err; /* We just unlocked. */
}
mutex_lock(&mapping->i_mmap_mutex);
flush_dcache_mmap_lock(mapping);
@@ -237,6 +237,10 @@ 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..d275e05 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -999,7 +999,7 @@ 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 do_mmap_pgoff_unlock(struct file *file, unsigned long addr,
unsigned long len, unsigned long prot,
unsigned long flags, unsigned long pgoff)
{
@@ -1017,31 +1017,39 @@ 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_unlock;
+ }
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_unlock;
+ }
/* offset overflow? */
- if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
- return -EOVERFLOW;
+ if ((pgoff + (len >> PAGE_SHIFT)) < pgoff) {
+ addr = -EOVERFLOW;
+ goto out_unlock;
+ }
/* 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_unlock;
+ }
/* 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_unlock;
/* 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 +1058,12 @@ 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_unlock;
+ }
+ }
/* mlock MCL_FUTURE? */
if (vm_flags & VM_LOCKED) {
@@ -1061,8 +1072,10 @@ 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_unlock;
+ }
}
inode = file ? file->f_path.dentry->d_inode : NULL;
@@ -1070,21 +1083,27 @@ 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_unlock;
+ }
/*
* 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_unlock;
+ }
/*
* 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_unlock;
+ }
vm_flags |= VM_SHARED | VM_MAYSHARE;
if (!(file->f_mode & FMODE_WRITE))
@@ -1092,20 +1111,27 @@ 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_unlock;
+ }
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_unlock;
+ }
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_unlock;
+ }
break;
default:
- return -EINVAL;
+ addr = -EINVAL;
+ goto out_unlock;
}
} else {
switch (flags & MAP_TYPE) {
@@ -1123,11 +1149,16 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
pgoff = addr >> PAGE_SHIFT;
break;
default:
- return -EINVAL;
+ addr = -EINVAL;
+ goto out_unlock;
}
}
- return mmap_region(file, addr, len, flags, vm_flags, pgoff);
+ return mmap_region_unlock(file, addr, len, flags, vm_flags, pgoff);
+
+out_unlock:
+ up_write(&mm->mmap_sem);
+ return addr;
}
SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
@@ -1240,9 +1271,9 @@ 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_unlock(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;
@@ -1251,19 +1282,24 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
struct rb_node **rb_link, *rb_parent;
unsigned long charged = 0;
struct inode *inode = file ? file->f_path.dentry->d_inode : NULL;
+ bool downgraded = false;
/* Clear old maps */
error = -ENOMEM;
munmap_back:
if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) {
- if (do_munmap(mm, addr, len))
- return -ENOMEM;
+ if (do_munmap(mm, addr, len)) {
+ error = -ENOMEM;
+ goto unacct_error;
+ }
goto 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;
}
@@ -1372,15 +1410,27 @@ out:
perf_event_mmap(vma);
vm_stat_account(mm, vm_flags, file, len >> PAGE_SHIFT);
+
+ downgraded = false;
if (vm_flags & VM_LOCKED) {
+ downgrade_write(&mm->mmap_sem);
+ downgraded = true;
if (!mlock_vma_pages_range(vma, addr, addr + len))
mm->locked_vm += (len >> PAGE_SHIFT);
- } else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK))
+ } else if ((flags & MAP_POPULATE) && !(flags & MAP_NONBLOCK)) {
+ downgrade_write(&mm->mmap_sem);
+ downgraded = true;
make_pages_present(addr, addr + len);
+ }
if (file)
uprobe_mmap(vma);
+ if (downgraded)
+ up_read(&mm->mmap_sem);
+ else
+ up_write(&mm->mmap_sem);
+
return addr;
unmap_and_free_vma:
@@ -1397,6 +1447,9 @@ free_vma:
unacct_error:
if (charged)
vm_unacct_memory(charged);
+
+ up_write(&mm->mmap_sem);
+
return error;
}
diff --git a/mm/util.c b/mm/util.c
index dc3036c..fd54884 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -359,8 +359,7 @@ 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_unlock(file, addr, len, prot, flag, pgoff);
}
return ret;
}
--
1.7.11.7
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