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author | Hugh Dickins <hughd@google.com> | 2014-06-23 13:22:06 -0700 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-07-28 07:06:44 -0700 |
commit | a62f374abb72830e1319d45ecb5e597b1944c8cd (patch) | |
tree | a6618ed9e255dc90ab5505d724ebaa1f58038f58 /mm | |
parent | 64fb4e2b0f802ac31f7350fbcba01de67845d4fb (diff) | |
download | lwn-a62f374abb72830e1319d45ecb5e597b1944c8cd.tar.gz lwn-a62f374abb72830e1319d45ecb5e597b1944c8cd.zip |
shmem: fix faulting into a hole while it's punched
commit f00cdc6df7d7cfcabb5b740911e6788cb0802bdb 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>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/shmem.c | 91 | ||||
-rw-r--r-- | mm/truncate.c | 25 |
2 files changed, 91 insertions, 25 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 58c4a477be67..352d511a90d9 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -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) diff --git a/mm/truncate.c b/mm/truncate.c index 4224627695ba..f38055cb8af6 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -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 |