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Subject[PATCH] mm: be sure to trim blocks after direct_io has failed
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This is updated version of patch aimed to fix direct_io error handling issue
i've previously sent 2 wheeks ago. If you don't like anything in this patch
plese let me know.

Changes:
- comments added. I think now it is clearly describe things.
- patch prepared against 2.6.20-mm2

How this patch tested:
- LTP test, and other readv/writev op tests.
- fsstress test.
- manual direct_io tests.

Log:
- Move common segment checks to separate helper function.
- Trim off blocks after generic_file_direct_write() has failed.
- Update out of date comments about direct_io locking rules.

Signed-off-by: Monakhov Dmitriy <dmonakhov@openvz.org>
---
mm/filemap.c | 107 +++++++++++++++++++++++++++++++++++----------------------
1 files changed, 66 insertions(+), 41 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index a9284c2..c81184c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1147,6 +1147,38 @@ success:
return size;
}

+/*
+ * Performs necessary checks before doing a write
+ *
+ * Adjust number of segments and amount of bytes to write.
+ * Returns appropriate error code that caller should return or
+ * zero in case that write should be allowed.
+ */
+int generic_segment_checks(const struct iovec *iov, unsigned long *nr_segs,
+ size_t *count, unsigned long access_flags)
+{
+ unsigned long seg;
+ for (seg = 0; seg < *nr_segs; seg++) {
+ const struct iovec *iv = &iov[seg];
+
+ /*
+ * If any segment has a negative length, or the cumulative
+ * length ever wraps negative then return -EINVAL.
+ */
+ *count += iv->iov_len;
+ if (unlikely((ssize_t)(*count|iv->iov_len) < 0))
+ return -EINVAL;
+ if (access_ok(access_flags, iv->iov_base, iv->iov_len))
+ continue;
+ if (seg == 0)
+ return -EFAULT;
+ *nr_segs = seg;
+ *count -= iv->iov_len; /* This segment is no good */
+ break;
+ }
+ return 0;
+}
+
/**
* generic_file_aio_read - generic filesystem read routine
* @iocb: kernel I/O control block
@@ -1168,24 +1200,9 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
loff_t *ppos = &iocb->ki_pos;

count = 0;
- for (seg = 0; seg < nr_segs; seg++) {
- const struct iovec *iv = &iov[seg];
-
- /*
- * If any segment has a negative length, or the cumulative
- * length ever wraps negative then return -EINVAL.
- */
- count += iv->iov_len;
- if (unlikely((ssize_t)(count|iv->iov_len) < 0))
- return -EINVAL;
- if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
- continue;
- if (seg == 0)
- return -EFAULT;
- nr_segs = seg;
- count -= iv->iov_len; /* This segment is no good */
- break;
- }
+ retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
+ if (retval)
+ return retval;

/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
if (filp->f_flags & O_DIRECT) {
@@ -2080,8 +2097,9 @@ generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
/*
* Sync the fs metadata but not the minor inode changes and
* of course not the data as we did direct DMA for the IO.
- * i_mutex is held, which protects generic_osync_inode() from
- * livelocking. AIO O_DIRECT ops attempt to sync metadata here.
+ * i_mutex may not being held, if so some specific locking
+ * ordering must protect generic_osync_inode() from livelocking.
+ * AIO O_DIRECT ops attempt to sync metadata here.
*/
if ((written >= 0 || written == -EIOCBQUEUED) &&
((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
@@ -2271,30 +2289,14 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
size_t ocount; /* original count */
size_t count; /* after file limit checks */
struct inode *inode = mapping->host;
- unsigned long seg;
loff_t pos;
ssize_t written;
ssize_t err;

ocount = 0;
- for (seg = 0; seg < nr_segs; seg++) {
- const struct iovec *iv = &iov[seg];
-
- /*
- * If any segment has a negative length, or the cumulative
- * length ever wraps negative then return -EINVAL.
- */
- ocount += iv->iov_len;
- if (unlikely((ssize_t)(ocount|iv->iov_len) < 0))
- return -EINVAL;
- if (access_ok(VERIFY_READ, iv->iov_base, iv->iov_len))
- continue;
- if (seg == 0)
- return -EFAULT;
- nr_segs = seg;
- ocount -= iv->iov_len; /* This segment is no good */
- break;
- }
+ err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
+ if (err)
+ return err;
if (unlikely(aio_restarted())) {
/* nothing to transfer, may just need to sync data */
return ocount;
@@ -2420,6 +2422,29 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
mutex_lock(&inode->i_mutex);
ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
&iocb->ki_pos);
+ /*
+ * If __generic_file_aio_write_nolock has failed.
+ * This may happen because of:
+ * 1) Bad segment found (failed before actual write attempt)
+ * 2) Segments are good, but actual write operation failed
+ * and may have instantiated a few blocks outside i_size.
+ * a) in case of buffered write these blocks was already
+ * trimmed by generic_file_buffered_write()
+ * b) in case of O_DIRECT these blocks weren't trimmed yet.
+ *
+ * In case of (2b) these blocks have to be trimmed off again.
+ */
+ if (unlikely( ret < 0 && file->f_flags & O_DIRECT)) {
+ unsigned long nr_segs_avail = nr_segs;
+ size_t count = 0;
+ if (!generic_segment_checks(iov, &nr_segs_avail, &count,
+ VERIFY_READ)) {
+ /*It is (2b) case, because segments are good*/
+ loff_t isize = i_size_read(inode);
+ if (pos + count > isize)
+ vmtruncate(inode, isize);
+ }
+ }
mutex_unlock(&inode->i_mutex);

if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
@@ -2436,8 +2461,8 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
EXPORT_SYMBOL(generic_file_aio_write);

/*
- * Called under i_mutex for writes to S_ISREG files. Returns -EIO if something
- * went wrong during pagecache shootdown.
+ * May be called without i_mutex for writes to S_ISREG files.
+ * Returns -EIO if something went wrong during pagecache shootdown.
*/
static ssize_t
generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
--
1.5.0.1
-
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