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Message-Id: <1479980796-26161-6-git-send-email-jack@suse.cz>
Date: Thu, 24 Nov 2016 10:46:35 +0100
From: Jan Kara <jack@...e.cz>
To: <linux-fsdevel@...r.kernel.org>
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>,
<linux-ext4@...r.kernel.org>, <linux-mm@...ck.org>,
linux-nvdimm@...ts.01.org, Johannes Weiner <hannes@...xchg.org>,
Jan Kara <jack@...e.cz>
Subject: [PATCH 5/6] dax: Call ->iomap_begin without entry lock during dax fault
Currently ->iomap_begin() handler is called with entry lock held. If the
filesystem held any locks between ->iomap_begin() and ->iomap_end()
(such as ext4 which will want to hold transaction open), this would cause
lock inversion with the iomap_apply() from standard IO path which first
calls ->iomap_begin() and only then calls ->actor() callback which grabs
entry locks for DAX.
Fix the problem by nesting grabbing of entry lock inside ->iomap_begin()
- ->iomap_end() pair.
Signed-off-by: Jan Kara <jack@...e.cz>
---
fs/dax.c | 120 ++++++++++++++++++++++++++++++++++-----------------------------
1 file changed, 65 insertions(+), 55 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 38f996976ebf..be39633d346e 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1077,6 +1077,15 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
}
EXPORT_SYMBOL_GPL(dax_iomap_rw);
+static int dax_fault_return(int error)
+{
+ if (error == 0)
+ return VM_FAULT_NOPAGE;
+ if (error == -ENOMEM)
+ return VM_FAULT_OOM;
+ return VM_FAULT_SIGBUS;
+}
+
/**
* dax_iomap_fault - handle a page fault on a DAX file
* @vma: The virtual memory area where the fault occurred
@@ -1109,12 +1118,6 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
if (pos >= i_size_read(inode))
return VM_FAULT_SIGBUS;
- entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
- if (IS_ERR(entry)) {
- error = PTR_ERR(entry);
- goto out;
- }
-
if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page)
flags |= IOMAP_WRITE;
@@ -1125,9 +1128,15 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
*/
error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
if (error)
- goto unlock_entry;
+ return dax_fault_return(error);
if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) {
- error = -EIO; /* fs corruption? */
+ vmf_ret = dax_fault_return(-EIO); /* fs corruption? */
+ goto finish_iomap;
+ }
+
+ entry = grab_mapping_entry(mapping, vmf->pgoff, 0);
+ if (IS_ERR(entry)) {
+ vmf_ret = dax_fault_return(PTR_ERR(entry));
goto finish_iomap;
}
@@ -1150,13 +1159,13 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
}
if (error)
- goto finish_iomap;
+ goto error_unlock_entry;
__SetPageUptodate(vmf->cow_page);
vmf_ret = finish_fault(vmf);
if (!vmf_ret)
vmf_ret = VM_FAULT_DONE_COW;
- goto finish_iomap;
+ goto unlock_entry;
}
switch (iomap.type) {
@@ -1168,12 +1177,15 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
}
error = dax_insert_mapping(mapping, iomap.bdev, sector,
PAGE_SIZE, &entry, vma, vmf);
+ /* -EBUSY is fine, somebody else faulted on the same PTE */
+ if (error == -EBUSY)
+ error = 0;
break;
case IOMAP_UNWRITTEN:
case IOMAP_HOLE:
if (!(vmf->flags & FAULT_FLAG_WRITE)) {
vmf_ret = dax_load_hole(mapping, &entry, vmf);
- goto finish_iomap;
+ goto unlock_entry;
}
/*FALLTHRU*/
default:
@@ -1182,30 +1194,25 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
break;
}
- finish_iomap:
- if (ops->iomap_end) {
- if (error || (vmf_ret & VM_FAULT_ERROR)) {
- /* keep previous error */
- ops->iomap_end(inode, pos, PAGE_SIZE, 0, flags,
- &iomap);
- } else {
- error = ops->iomap_end(inode, pos, PAGE_SIZE,
- PAGE_SIZE, flags, &iomap);
- }
- }
+ error_unlock_entry:
+ vmf_ret = dax_fault_return(error) | major;
unlock_entry:
put_locked_mapping_entry(mapping, vmf->pgoff, entry);
- out:
- if (error == -ENOMEM)
- return VM_FAULT_OOM | major;
- /* -EBUSY is fine, somebody else faulted on the same PTE */
- if (error < 0 && error != -EBUSY)
- return VM_FAULT_SIGBUS | major;
- if (vmf_ret) {
- WARN_ON_ONCE(error); /* -EBUSY from ops->iomap_end? */
- return vmf_ret;
+ finish_iomap:
+ if (ops->iomap_end) {
+ int copied = PAGE_SIZE;
+
+ if (vmf_ret & VM_FAULT_ERROR)
+ copied = 0;
+ /*
+ * The fault is done by now and there's no way back (other
+ * thread may be already happily using PTE we have installed).
+ * Just ignore error from ->iomap_end since we cannot do much
+ * with it.
+ */
+ ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap);
}
- return VM_FAULT_NOPAGE | major;
+ return vmf_ret;
}
EXPORT_SYMBOL_GPL(dax_iomap_fault);
@@ -1330,6 +1337,15 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
goto fallback;
/*
+ * Note that we don't use iomap_apply here. We aren't doing I/O, only
+ * setting up a mapping, so really we're using iomap_begin() as a way
+ * to look up our filesystem block.
+ */
+ pos = (loff_t)pgoff << PAGE_SHIFT;
+ error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap);
+ if (error)
+ goto fallback;
+ /*
* grab_mapping_entry() will make sure we get a 2M empty entry, a DAX
* PMD or a HZP entry. If it can't (because a 4k page is already in
* the tree, for instance), it will return -EEXIST and we just fall
@@ -1337,19 +1353,10 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
*/
entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD);
if (IS_ERR(entry))
- goto fallback;
+ goto finish_iomap;
- /*
- * Note that we don't use iomap_apply here. We aren't doing I/O, only
- * setting up a mapping, so really we're using iomap_begin() as a way
- * to look up our filesystem block.
- */
- pos = (loff_t)pgoff << PAGE_SHIFT;
- error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap);
- if (error)
- goto unlock_entry;
if (iomap.offset + iomap.length < pos + PMD_SIZE)
- goto finish_iomap;
+ goto unlock_entry;
vmf.pgoff = pgoff;
vmf.flags = flags;
@@ -1363,7 +1370,7 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
case IOMAP_UNWRITTEN:
case IOMAP_HOLE:
if (WARN_ON_ONCE(write))
- goto finish_iomap;
+ goto unlock_entry;
result = dax_pmd_load_hole(vma, pmd, &vmf, address, &iomap,
&entry);
break;
@@ -1372,20 +1379,23 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
break;
}
+ unlock_entry:
+ put_locked_mapping_entry(mapping, pgoff, entry);
finish_iomap:
if (ops->iomap_end) {
- if (result == VM_FAULT_FALLBACK) {
- ops->iomap_end(inode, pos, PMD_SIZE, 0, iomap_flags,
- &iomap);
- } else {
- error = ops->iomap_end(inode, pos, PMD_SIZE, PMD_SIZE,
- iomap_flags, &iomap);
- if (error)
- result = VM_FAULT_FALLBACK;
- }
+ int copied = PMD_SIZE;
+
+ if (result == VM_FAULT_FALLBACK)
+ copied = 0;
+ /*
+ * The fault is done by now and there's no way back (other
+ * thread may be already happily using PMD we have installed).
+ * Just ignore error from ->iomap_end since we cannot do much
+ * with it.
+ */
+ ops->iomap_end(inode, pos, PMD_SIZE, copied, iomap_flags,
+ &iomap);
}
- unlock_entry:
- put_locked_mapping_entry(mapping, pgoff, entry);
fallback:
if (result == VM_FAULT_FALLBACK) {
split_huge_pmd(vma, pmd, address);
--
2.6.6
--
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