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shmem: fix faulting into a hole while it's punched 

commit f00cdc6df7 upstream.

Trinity finds that mmap access to a hole while it's punched from shmem
can prevent the madvise(MADV_REMOVE) or fallocate(FALLOC_FL_PUNCH_HOLE)
from completing, until the reader chooses to stop; with the puncher's
hold on i_mutex locking out all other writers until it can complete.

It appears that the tmpfs fault path is too light in comparison with its
hole-punching path, lacking an i_data_sem to obstruct it; but we don't
want to slow down the common case.

Extend shmem_fallocate()'s existing range notification mechanism, so
shmem_fault() can refrain from faulting pages into the hole while it's
punched, waiting instead on i_mutex (when safe to sleep; or repeatedly
faulting when not).

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Dave Jones <davej@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Hugh Dickins 2014-06-23 13:22:06 -07:00 committed by Greg Kroah-Hartman
parent 64fb4e2b0f
commit a62f374abb
2 changed files with 91 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

91
mm/shmem.c
View File

@ -76,6 +76,16 @@ static struct vfsmount *shm_mnt;
/* Symlink up to this size is kmalloc'ed instead of using a swappable page */
#define SHORT_SYMLINK_LEN 128
/*
* vmtruncate_range() communicates with shmem_fault via
* inode->i_private (with i_mutex making sure that it has only one user at
* a time): we would prefer not to enlarge the shmem inode just for that.
*/
struct shmem_falloc {
pgoff_t start; /* start of range currently being fallocated */
pgoff_t next; /* the next page offset to be fallocated */
};
struct shmem_xattr {
struct list_head list; /* anchored by shmem_inode_info->xattr_list */
char *name; /* xattr name */
@ -1060,6 +1070,43 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
int error;
int ret = VM_FAULT_LOCKED;
/*
* Trinity finds that probing a hole which tmpfs is punching can
* prevent the hole-punch from ever completing: which in turn
* locks writers out with its hold on i_mutex. So refrain from
* faulting pages into the hole while it's being punched, and
* wait on i_mutex to be released if vmf->flags permits.
*/
if (unlikely(inode->i_private)) {
struct shmem_falloc *shmem_falloc;
spin_lock(&inode->i_lock);
shmem_falloc = inode->i_private;
if (!shmem_falloc ||
vmf->pgoff < shmem_falloc->start ||
vmf->pgoff >= shmem_falloc->next)
shmem_falloc = NULL;
spin_unlock(&inode->i_lock);
/*
* i_lock has protected us from taking shmem_falloc seriously
* once return from vmtruncate_range() went back up that stack.
* i_lock does not serialize with i_mutex at all, but it does
* not matter if sometimes we wait unnecessarily, or sometimes
* miss out on waiting: we just need to make those cases rare.
*/
if (shmem_falloc) {
if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
up_read(&vma->vm_mm->mmap_sem);
mutex_lock(&inode->i_mutex);
mutex_unlock(&inode->i_mutex);
return VM_FAULT_RETRY;
}
/* cond_resched? Leave that to GUP or return to user */
return VM_FAULT_NOPAGE;
}
}
error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
if (error)
return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
@ -1071,6 +1118,44 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
return ret;
}
int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
/*
* If the underlying filesystem is not going to provide
* a way to truncate a range of blocks (punch a hole) -
* we should return failure right now.
* Only CONFIG_SHMEM shmem.c ever supported i_op->truncate_range().
*/
if (inode->i_op->truncate_range != shmem_truncate_range)
return -ENOSYS;
mutex_lock(&inode->i_mutex);
{
struct shmem_falloc shmem_falloc;
struct address_space *mapping = inode->i_mapping;
loff_t unmap_start = round_up(lstart, PAGE_SIZE);
loff_t unmap_end = round_down(1 + lend, PAGE_SIZE) - 1;
shmem_falloc.start = unmap_start >> PAGE_SHIFT;
shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
spin_lock(&inode->i_lock);
inode->i_private = &shmem_falloc;
spin_unlock(&inode->i_lock);
if ((u64)unmap_end > (u64)unmap_start)
unmap_mapping_range(mapping, unmap_start,
1 + unmap_end - unmap_start, 0);
shmem_truncate_range(inode, lstart, lend);
/* No need to unmap again: hole-punching leaves COWed pages */
spin_lock(&inode->i_lock);
inode->i_private = NULL;
spin_unlock(&inode->i_lock);
}
mutex_unlock(&inode->i_mutex);
return 0;
}
#ifdef CONFIG_NUMA
static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *mpol)
{
@ -2547,6 +2632,12 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
}
EXPORT_SYMBOL_GPL(shmem_truncate_range);
int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
/* Only CONFIG_SHMEM shmem.c ever supported i_op->truncate_range(). */
return -ENOSYS;
}
#define shmem_vm_ops generic_file_vm_ops
#define shmem_file_operations ramfs_file_operations
#define shmem_get_inode(sb, dir, mode, dev, flags) ramfs_get_inode(sb, dir, mode, dev)

25
mm/truncate.c
View File

@ -603,31 +603,6 @@ int vmtruncate(struct inode *inode, loff_t newsize)
}
EXPORT_SYMBOL(vmtruncate);
int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend)
{
struct address_space *mapping = inode->i_mapping;
loff_t holebegin = round_up(lstart, PAGE_SIZE);
loff_t holelen = 1 + lend - holebegin;
/*
* If the underlying filesystem is not going to provide
* a way to truncate a range of blocks (punch a hole) -
* we should return failure right now.
*/
if (!inode->i_op->truncate_range)
return -ENOSYS;
mutex_lock(&inode->i_mutex);
inode_dio_wait(inode);
unmap_mapping_range(mapping, holebegin, holelen, 1);
inode->i_op->truncate_range(inode, lstart, lend);
/* unmap again to remove racily COWed private pages */
unmap_mapping_range(mapping, holebegin, holelen, 1);
mutex_unlock(&inode->i_mutex);
return 0;
}
/**
* truncate_pagecache_range - unmap and remove pagecache that is hole-punched
* @inode: inode