From: Filipe Manana fdmanana@suse.com
commit 8184620ae21213d51eaf2e0bd4186baacb928172 upstream.
When doing a direct IO write using a iocb with nowait and dsync set, we end up not syncing the file once the write completes.
This is because we tell iomap to not call generic_write_sync(), which would result in calling btrfs_sync_file(), in order to avoid a deadlock since iomap can call it while we are holding the inode's lock and btrfs_sync_file() needs to acquire the inode's lock. The deadlock happens only if the write happens synchronously, when iomap_dio_rw() calls iomap_dio_complete() before it returns. Instead we do the sync ourselves at btrfs_do_write_iter().
For a nowait write however we can end up not doing the sync ourselves at at btrfs_do_write_iter() because the write could have been queued, and therefore we get -EIOCBQUEUED returned from iomap in such case. That makes us skip the sync call at btrfs_do_write_iter(), as we don't do it for any error returned from btrfs_direct_write(). We can't simply do the call even if -EIOCBQUEUED is returned, since that would block the task waiting for IO, both for the data since there are bios still in progress as well as potentially blocking when joining a log transaction and when syncing the log (writing log trees, super blocks, etc).
So let iomap do the sync call itself and in order to avoid deadlocks for the case of synchronous writes (without nowait), use __iomap_dio_rw() and have ourselves call iomap_dio_complete() after unlocking the inode.
A test case will later be sent for fstests, after this is fixed in Linus' tree.
Fixes: 51bd9563b678 ("btrfs: fix deadlock due to page faults during direct IO reads and writes") Reported-by: Марк Коренберг socketpair@gmail.com Link: https://lore.kernel.org/linux-btrfs/CAEmTpZGRKbzc16fWPvxbr6AfFsQoLmz-Lcg-7Og... CC: stable@vger.kernel.org # 6.0+ Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/ctree.h | 5 ++++- fs/btrfs/file.c | 22 ++++++++++++++++------ fs/btrfs/inode.c | 14 +++++++++++--- 3 files changed, 31 insertions(+), 10 deletions(-)
--- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -3407,7 +3407,10 @@ ssize_t btrfs_encoded_read(struct kiocb ssize_t btrfs_do_encoded_write(struct kiocb *iocb, struct iov_iter *from, const struct btrfs_ioctl_encoded_io_args *encoded);
-ssize_t btrfs_dio_rw(struct kiocb *iocb, struct iov_iter *iter, size_t done_before); +ssize_t btrfs_dio_read(struct kiocb *iocb, struct iov_iter *iter, + size_t done_before); +struct iomap_dio *btrfs_dio_write(struct kiocb *iocb, struct iov_iter *iter, + size_t done_before);
extern const struct dentry_operations btrfs_dentry_operations;
--- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1889,6 +1889,7 @@ static ssize_t btrfs_direct_write(struct loff_t endbyte; ssize_t err; unsigned int ilock_flags = 0; + struct iomap_dio *dio;
if (iocb->ki_flags & IOCB_NOWAIT) ilock_flags |= BTRFS_ILOCK_TRY; @@ -1949,11 +1950,22 @@ relock: * So here we disable page faults in the iov_iter and then retry if we * got -EFAULT, faulting in the pages before the retry. */ -again: from->nofault = true; - err = btrfs_dio_rw(iocb, from, written); + dio = btrfs_dio_write(iocb, from, written); from->nofault = false;
+ /* + * iomap_dio_complete() will call btrfs_sync_file() if we have a dsync + * iocb, and that needs to lock the inode. So unlock it before calling + * iomap_dio_complete() to avoid a deadlock. + */ + btrfs_inode_unlock(inode, ilock_flags); + + if (IS_ERR_OR_NULL(dio)) + err = PTR_ERR_OR_ZERO(dio); + else + err = iomap_dio_complete(dio); + /* No increment (+=) because iomap returns a cumulative value. */ if (err > 0) written = err; @@ -1979,12 +1991,10 @@ again: } else { fault_in_iov_iter_readable(from, left); prev_left = left; - goto again; + goto relock; } }
- btrfs_inode_unlock(inode, ilock_flags); - /* * If 'err' is -ENOTBLK or we have not written all data, then it means * we must fallback to buffered IO. @@ -3787,7 +3797,7 @@ again: */ pagefault_disable(); to->nofault = true; - ret = btrfs_dio_rw(iocb, to, read); + ret = btrfs_dio_read(iocb, to, read); to->nofault = false; pagefault_enable();
--- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8241,13 +8241,21 @@ static const struct iomap_dio_ops btrfs_ .bio_set = &btrfs_dio_bioset, };
-ssize_t btrfs_dio_rw(struct kiocb *iocb, struct iov_iter *iter, size_t done_before) +ssize_t btrfs_dio_read(struct kiocb *iocb, struct iov_iter *iter, size_t done_before) { struct btrfs_dio_data data;
return iomap_dio_rw(iocb, iter, &btrfs_dio_iomap_ops, &btrfs_dio_ops, - IOMAP_DIO_PARTIAL | IOMAP_DIO_NOSYNC, - &data, done_before); + IOMAP_DIO_PARTIAL, &data, done_before); +} + +struct iomap_dio *btrfs_dio_write(struct kiocb *iocb, struct iov_iter *iter, + size_t done_before) +{ + struct btrfs_dio_data data; + + return __iomap_dio_rw(iocb, iter, &btrfs_dio_iomap_ops, &btrfs_dio_ops, + IOMAP_DIO_PARTIAL, &data, done_before); }
static int btrfs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,