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fix mremap() vs. ioctx_kill() race

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teach ->mremap() method to return an error and have it fail for
aio mappings in process of being killed

Note that in case of ->mremap() failure we need to undo move_page_tables()
we'd already done; we could call ->mremap() first, but then the failure of
move_page_tables() would require undoing whatever _successful_ ->mremap()
has done, which would be a lot more headache in general.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2015-04-06 17:48:54 -04:00
parent 8f778bbc54
commit b2edffdd91
3 changed files with 21 additions and 10 deletions
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19
fs/aio.c
View file

@ -278,11 +278,11 @@ static int aio_ring_mmap(struct file *file, struct vm_area_struct *vma)
return 0;
}
static void aio_ring_remap(struct file *file, struct vm_area_struct *vma)
static int aio_ring_remap(struct file *file, struct vm_area_struct *vma)
{
struct mm_struct *mm = vma->vm_mm;
struct kioctx_table *table;
int i;
int i, res = -EINVAL;
spin_lock(&mm->ioctx_lock);
rcu_read_lock();
@ -292,13 +292,17 @@ static void aio_ring_remap(struct file *file, struct vm_area_struct *vma)
ctx = table->table[i];
if (ctx && ctx->aio_ring_file == file) {
ctx->user_id = ctx->mmap_base = vma->vm_start;
if (!atomic_read(&ctx->dead)) {
ctx->user_id = ctx->mmap_base = vma->vm_start;
res = 0;
}
break;
}
}
rcu_read_unlock();
spin_unlock(&mm->ioctx_lock);
return res;
}
static const struct file_operations aio_ring_fops = {
@ -748,11 +752,12 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
{
struct kioctx_table *table;
if (atomic_xchg(&ctx->dead, 1))
return -EINVAL;
spin_lock(&mm->ioctx_lock);
if (atomic_xchg(&ctx->dead, 1)) {
spin_unlock(&mm->ioctx_lock);
return -EINVAL;
}
table = rcu_dereference_raw(mm->ioctx_table);
WARN_ON(ctx != table->table[ctx->id]);
table->table[ctx->id] = NULL;

2
include/linux/fs.h
View file

@ -1549,7 +1549,7 @@ struct file_operations {
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
void (*mremap)(struct file *, struct vm_area_struct *);
int (*mremap)(struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);

10
mm/mremap.c
View file

@ -286,8 +286,14 @@ static unsigned long move_vma(struct vm_area_struct *vma,
old_len = new_len;
old_addr = new_addr;
new_addr = -ENOMEM;
} else if (vma->vm_file && vma->vm_file->f_op->mremap)
vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
} else if (vma->vm_file && vma->vm_file->f_op->mremap) {
err = vma->vm_file->f_op->mremap(vma->vm_file, new_vma);
if (err < 0) {
move_page_tables(new_vma, new_addr, vma, old_addr,
moved_len, true);
return err;
}
}
/* Conceal VM_ACCOUNT so old reservation is not undone */
if (vm_flags & VM_ACCOUNT) {