From 8184620ae21213d51eaf2e0bd4186baacb928172 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Fri, 28 Oct 2022 13:15:35 +0100 Subject: btrfs: fix lost file sync on direct IO write with nowait and dsync iocb MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Link: https://lore.kernel.org/linux-btrfs/CAEmTpZGRKbzc16fWPvxbr6AfFsQoLmz-Lcg-7OgJOZDboJ+SGQ@mail.gmail.com/ CC: stable@vger.kernel.org # 6.0+ Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/file.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) (limited to 'fs/btrfs/file.c') diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 176b432035ae..d55ad46384d1 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1765,6 +1765,7 @@ static ssize_t btrfs_direct_write(struct kiocb *iocb, struct iov_iter *from) 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; @@ -1825,11 +1826,22 @@ 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; @@ -1855,12 +1867,10 @@ 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. @@ -4035,7 +4045,7 @@ 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(); -- cgit v1.2.3 From a348c8d4f6cf23ef04b0edaccdfe9d94c2d335db Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Wed, 2 Nov 2022 12:46:35 +0000 Subject: btrfs: fix nowait buffered write returning -ENOSPC If we are doing a buffered write in NOWAIT context and we can't reserve metadata space due to -ENOSPC, then we should return -EAGAIN so that we retry the write in a context allowed to block and do metadata reservation with flushing, which might succeed this time due to the allowed flushing. Returning -ENOSPC while in NOWAIT context simply makes some writes fail with -ENOSPC when they would likely succeed after switching from NOWAIT context to blocking context. That is unexpected behaviour and even fio complains about it with a warning like this: fio: io_u error on file /mnt/sdi/task_0.0.0: No space left on device: write offset=1535705088, buflen=65536 fio: pid=592630, err=28/file:io_u.c:1846, func=io_u error, error=No space left on device The fio's job config is this: [global] bs=64K ioengine=io_uring iodepth=1 size=2236962133 nr_files=1 filesize=2236962133 direct=0 runtime=10 fallocate=posix io_size=2236962133 group_reporting time_based [task_0] rw=randwrite directory=/mnt/sdi numjobs=4 So fix this by returning -EAGAIN if we are in NOWAIT context and the metadata reservation failed with -ENOSPC. Fixes: 304e45acdb8f ("btrfs: plumb NOWAIT through the write path") Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/file.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'fs/btrfs/file.c') diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index d55ad46384d1..5ce2ae9d4f72 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1598,6 +1598,9 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, write_bytes); else btrfs_check_nocow_unlock(BTRFS_I(inode)); + + if (nowait && ret == -ENOSPC) + ret = -EAGAIN; break; } -- cgit v1.2.3 From eb81b682b131642405a05c627ab08cf0967b3dd8 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Wed, 2 Nov 2022 12:46:36 +0000 Subject: btrfs: fix inode reserve space leak due to nowait buffered write During a nowait buffered write, if we fail to balance dirty pages we exit btrfs_buffered_write() without releasing the delalloc space reserved for an extent, resulting in leaking space from the inode's block reserve. So fix that by releasing the delalloc space for the extent when balancing dirty pages fails. Reported-by: kernel test robot Link: https://lore.kernel.org/all/202210111304.d369bc32-yujie.liu@intel.com Fixes: 965f47aeb5de ("btrfs: make btrfs_buffered_write nowait compatible") Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba --- fs/btrfs/file.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'fs/btrfs/file.c') diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 5ce2ae9d4f72..d01631d47806 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1607,8 +1607,10 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb, release_bytes = reserve_bytes; again: ret = balance_dirty_pages_ratelimited_flags(inode->i_mapping, bdp_flags); - if (ret) + if (ret) { + btrfs_delalloc_release_extents(BTRFS_I(inode), reserve_bytes); break; + } /* * This is going to setup the pages array with the number of -- cgit v1.2.3