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List: linux-mm-commits
Subject: + shmem-fix-faulting-into-a-hole-while-its-punched.patch added to -mm tree
From: akpm () linux-foundation ! org
Date: 2014-06-17 20:37:32
Message-ID: 53a0a70c.3Gp5lI+tZ+aP1wo6%akpm () linux-foundation ! org
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The patch titled
Subject: shmem: fix faulting into a hole while it's punched
has been added to the -mm tree. Its filename is
shmem-fix-faulting-into-a-hole-while-its-punched.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/shmem-fix-faulting-into-a-hole-while-its-punched.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/shmem-fix-faulting-into-a-hole-while-its-punched.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: shmem: fix faulting into a hole while it's punched
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).
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>
---
mm/shmem.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 51 insertions(+), 4 deletions(-)
diff -puN mm/shmem.c~shmem-fix-faulting-into-a-hole-while-its-punched mm/shmem.c
--- a/mm/shmem.c~shmem-fix-faulting-into-a-hole-while-its-punched
+++ a/mm/shmem.c
@@ -80,11 +80,12 @@ static struct vfsmount *shm_mnt;
#define SHORT_SYMLINK_LEN 128
/*
- * shmem_fallocate and shmem_writepage communicate 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.
+ * shmem_fallocate communicates with shmem_fault or shmem_writepage 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 {
+ int mode; /* FALLOC_FL mode currently operating */
pgoff_t start; /* start of range currently being fallocated */
pgoff_t next; /* the next page offset to be fallocated */
pgoff_t nr_falloced; /* how many new pages have been fallocated */
@@ -759,6 +760,7 @@ static int shmem_writepage(struct page *
spin_lock(&inode->i_lock);
shmem_falloc = inode->i_private;
if (shmem_falloc &&
+ !shmem_falloc->mode &&
index >= shmem_falloc->start &&
index < shmem_falloc->next)
shmem_falloc->nr_unswapped++;
@@ -1233,6 +1235,43 @@ static int shmem_fault(struct vm_area_st
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 ||
+ shmem_falloc->mode != FALLOC_FL_PUNCH_HOLE ||
+ 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 shmem_fallocate() 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);
@@ -1729,18 +1768,26 @@ static long shmem_fallocate(struct file
mutex_lock(&inode->i_mutex);
+ shmem_falloc.mode = mode & ~FALLOC_FL_KEEP_SIZE;
+
if (mode & FALLOC_FL_PUNCH_HOLE) {
struct address_space *mapping = file->f_mapping;
loff_t unmap_start = round_up(offset, PAGE_SIZE);
loff_t unmap_end = round_down(offset + len, 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, offset, offset + len - 1);
/* No need to unmap again: hole-punching leaves COWed pages */
error = 0;
- goto out;
+ goto undone;
}
/* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
_
Patches currently in -mm which might be from hughd@google.com are
tmpfs-zero_range-and-collapse_range-not-currently-supported.patch
hugetlb-fix-copy_hugetlb_page_range-to-handle-migration-hwpoisoned-entry.patch
mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep.patch
mm-thp-fix-debug_pagealloc-oops-in-copy_page_rep-checkpatch-fixes.patch
mm-let-mm_find_pmd-fix-buggy-race-with-thp-fault.patch
shmem-fix-faulting-into-a-hole-while-its-punched.patch
mm-memoryc-use-entry-=-access_oncepte-in-handle_pte_fault.patch
list-use-argument-hlist_add_after-names-from-rcu-variant.patch
list-fix-order-of-arguments-for-hlist_add_after_rcu.patch
klist-use-same-naming-scheme-as-hlist-for-klist_add_after.patch
mm-replace-remap_file_pages-syscall-with-emulation-fix-3.patch
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