On Mon, Jul 24, 2017 at 03:14:08PM +0200, David Sterba wrote: > On Mon, Jul 24, 2017 at 02:50:50PM +0200, David Sterba wrote: > > On Fri, Jul 21, 2017 at 01:29:08PM -0400, [email protected] wrote: > > > From: Josef Bacik <[email protected]> > > > > > > Readdir does dir_emit while under the btree lock. dir_emit can trigger > > > the page fault which means we can deadlock. Fix this by allocating a > > > buffer on opening a directory and copying the readdir into this buffer > > > and doing dir_emit from outside of the tree lock. > > > > > > Signed-off-by: Josef Bacik <[email protected]> > > > --- > > > fs/btrfs/inode.c | 110 > > > +++++++++++++++++++++++++++++++++++++++++-------------- > > > 1 file changed, 83 insertions(+), 27 deletions(-) > > > > > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c > > > index 9a4413a..61396e3 100644 > > > --- a/fs/btrfs/inode.c > > > +++ b/fs/btrfs/inode.c > > > @@ -5877,6 +5877,56 @@ unsigned char btrfs_filetype_table[] = { > > > DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR, DT_BLK, DT_FIFO, DT_SOCK, DT_LNK > > > }; > > > > > > +/* > > > + * All this infrastructure exists because dir_emit can fault, and we are > > > holding > > > + * the tree lock when doing readdir. For now just allocate a buffer and > > > copy > > > + * our information into that, and then dir_emit from the buffer. This is > > > + * similar to what NFS does, only we don't keep the buffer around in > > > pagecache > > > + * because I'm afraid I'll fuck that up. > > Can you please explain the concern in more detail? >
If we keep the cache I'll have to have mechanisms to invalidate the page cache so it can be regenerated at the next readdir. Then I also have to wire up releasepage and stuff for directories and make sure it doesn't do anything bonkers like accidently try to write the data out for a directory. All in all it's not worth the headache I don't think. Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
