From ff0fa73247e442518936baa43c3f037b17f10fa7 Mon Sep 17 00:00:00 2001 From: Goldwyn Rodrigues Date: Tue, 4 Jul 2017 22:33:07 -0500 Subject: [PATCH] btrfs: nowait aio: Correct assignment of pos Assigning pos for usage early messes up in append mode, where the pos is re-assigned in generic_write_checks(). Assign pos later to get the correct position to write from iocb->ki_pos. Since check_can_nocow also uses the value of pos, we shift generic_write_checks() before check_can_nocow(). Checks with IOCB_DIRECT are present in generic_write_checks(), so checking for IOCB_NOWAIT is enough. Also, put locking sequence in the fast path. This fixes a user visible bug, as reported: "apparently breaks several shell related features on my system. In zsh history stopped working, because no new entries are added anymore. I fist noticed the issue when I tried to build mplayer. It uses a shell script to generate a help_mp.h file: [...] Here is a simple testcase: % echo "foo" >> test % echo "foo" >> test % cat test foo % " Fixes: edf064e7c6fe ("btrfs: nowait aio support") CC: Jens Axboe Reported-by: Markus Trippelsdorf Link: https://lkml.kernel.org/r/20170704042306.GA274@x4 Signed-off-by: Goldwyn Rodrigues Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/file.c | 26 ++++++++++++++------------ 1 file changed, 14 insertions(+), 12 deletions(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 59e2dccdf75b..ad53832838b5 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1875,16 +1875,25 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb, ssize_t num_written = 0; bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host); ssize_t err; - loff_t pos = iocb->ki_pos; + loff_t pos; size_t count = iov_iter_count(from); loff_t oldsize; int clean_page = 0; - if ((iocb->ki_flags & IOCB_NOWAIT) && - (iocb->ki_flags & IOCB_DIRECT)) { - /* Don't sleep on inode rwsem */ - if (!inode_trylock(inode)) + if (!inode_trylock(inode)) { + if (iocb->ki_flags & IOCB_NOWAIT) return -EAGAIN; + inode_lock(inode); + } + + err = generic_write_checks(iocb, from); + if (err <= 0) { + inode_unlock(inode); + return err; + } + + pos = iocb->ki_pos; + if (iocb->ki_flags & IOCB_NOWAIT) { /* * We will allocate space in case nodatacow is not set, * so bail @@ -1895,13 +1904,6 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb, inode_unlock(inode); return -EAGAIN; } - } else - inode_lock(inode); - - err = generic_write_checks(iocb, from); - if (err <= 0) { - inode_unlock(inode); - return err; } current->backing_dev_info = inode_to_bdi(inode); -- 2.20.1