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From: Mark Harmstone <maharmstone@meta.com>
To: Pavel Begunkov <asml.silence@gmail.com>,
        Mark Harmstone
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CC: "io-uring@vger.kernel.org" <io-uring@vger.kernel.org>
Subject: Re: [PATCH 5/5] btrfs: add io_uring command for encoded reads
Thread-Topic: [PATCH 5/5] btrfs: add io_uring command for encoded reads
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Date: Thu, 31 Oct 2024 17:08:52 +0000
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 definitions=2024-10-05_03,2024-10-04_01,2024-09-30_01

Thanks Pavel.

On 30/10/24 00:59, Pavel Begunkov wrote:
> >=20
> On 10/22/24 15:50, Mark Harmstone wrote:
> ...
>> +static void btrfs_uring_read_finished(struct io_uring_cmd *cmd,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unsigned int issu=
e_flags)
>> +{
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_uring_priv *priv =3D
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 *io_uring_cmd_to_pdu(cmd, st=
ruct btrfs_uring_priv *);
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_inode *inode =3D BTRFS_I(file_inode(pri=
v->iocb.ki_filp));
>> +=C2=A0=C2=A0=C2=A0 struct extent_io_tree *io_tree =3D &inode->io_tree;
>> +=C2=A0=C2=A0=C2=A0 unsigned long i;
>> +=C2=A0=C2=A0=C2=A0 u64 cur;
>> +=C2=A0=C2=A0=C2=A0 size_t page_offset;
>> +=C2=A0=C2=A0=C2=A0 ssize_t ret;
>> +
>> +=C2=A0=C2=A0=C2=A0 if (priv->err) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D priv->err;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto out;
>> +=C2=A0=C2=A0=C2=A0 }
>> +
>> +=C2=A0=C2=A0=C2=A0 if (priv->compressed) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i =3D 0;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 page_offset =3D 0;
>> +=C2=A0=C2=A0=C2=A0 } else {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i =3D (priv->iocb.ki_pos - p=
riv->start) >> PAGE_SHIFT;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 page_offset =3D offset_in_pa=
ge(priv->iocb.ki_pos - priv->start);
>> +=C2=A0=C2=A0=C2=A0 }
>> +=C2=A0=C2=A0=C2=A0 cur =3D 0;
>> +=C2=A0=C2=A0=C2=A0 while (cur < priv->count) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 size_t bytes =3D min_t(size_=
t, priv->count - cur,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 PAGE_SIZE - page_offset=
);
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (copy_page_to_iter(priv->=
pages[i], page_offset, bytes,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 &priv->iter) !=3D=
 bytes) {
>=20
> If that's an iovec backed iter that might fail, you'd need to
> steal this patch
>=20
> https://lore.kernel.org/all/20241016-fuse-uring-for-6-10-rfc4-v4-12-9739c=
753666e@ddn.com/
>=20
> and fail if "issue_flags & IO_URING_F_TASK_DEAD", see
>=20
> https://lore.kernel.org/all/20241016-fuse-uring-for-6-10-rfc4-v4-13-9739c=
753666e@ddn.com/

Thanks, I've sent a patchset including your patch. Does it make a=20
difference, though? If the task has died, presumably copy_page_to_iter=20
can't copy to another process' memory...?

>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =
=3D -EFAULT;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto=
 out;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i++;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cur +=3D bytes;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 page_offset =3D 0;
>> +=C2=A0=C2=A0=C2=A0 }
>> +=C2=A0=C2=A0=C2=A0 ret =3D priv->count;
>> +
>> +out:
>> +=C2=A0=C2=A0=C2=A0 unlock_extent(io_tree, priv->start, priv->lockend,=20
>> &priv->cached_state);
>> +=C2=A0=C2=A0=C2=A0 btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
>=20
> When called via io_uring_cmd_complete_in_task() this function might
> not get run in any reasonable amount of time. Even worse, a
> misbehaving user can block it until the task dies.
>=20
> I don't remember if rwsem allows unlock being executed in a different
> task than the pairing lock, but blocking it for that long could be a
> problem. I might not remember it right but I think Boris meantioned
> that the O_DIRECT path drops the inode lock right after submission
> without waiting for bios to complete. Is that right? Can we do it
> here as well?

We can't release the inode lock until we've released the extent lock. I=20
do intend to look into reducing the amount of time we hold the extent=20
lock, if we can, but it's not trivial to do this in a safe manner.
We could perhaps move the unlocking to btrfs_uring_read_extent_endio=20
instead, but it looks unlocking an rwsem in a different context might=20
cause problems with PREEMPT_RT(?).

>> +
>> +=C2=A0=C2=A0=C2=A0 io_uring_cmd_done(cmd, ret, 0, issue_flags);
>> +=C2=A0=C2=A0=C2=A0 add_rchar(current, ret);
>> +
>> +=C2=A0=C2=A0=C2=A0 for (unsigned long index =3D 0; index < priv->nr_pag=
es; index++)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 __free_page(priv->pages[inde=
x]);
>> +
>> +=C2=A0=C2=A0=C2=A0 kfree(priv->pages);
>> +=C2=A0=C2=A0=C2=A0 kfree(priv->iov);
>> +=C2=A0=C2=A0=C2=A0 kfree(priv);
>> +}
>> +
>> +void btrfs_uring_read_extent_endio(void *ctx, int err)
>> +{
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_uring_priv *priv =3D ctx;
>> +
>> +=C2=A0=C2=A0=C2=A0 priv->err =3D err;
>> +
>> +=C2=A0=C2=A0=C2=A0 *io_uring_cmd_to_pdu(priv->cmd, struct btrfs_uring_p=
riv *) =3D priv;
>=20
> a nit, I'd suggest to create a temp var, should be easier to
> read. It'd even be nicer if you wrap it into a structure
> as suggested last time.
>=20
> struct io_btrfs_cmd {
>  =C2=A0=C2=A0=C2=A0=C2=A0struct btrfs_uring_priv *priv;
> };
>=20
> struct io_btrfs_cmd *bc =3D io_uring_cmd_to_pdu(cmd, struct io_btrfs_cmd);
> bc->priv =3D priv;

No problem, I've sent a patch for this.

>> +=C2=A0=C2=A0=C2=A0 io_uring_cmd_complete_in_task(priv->cmd, btrfs_uring=
_read_finished);
>> +}
>> +
>> +static int btrfs_uring_read_extent(struct kiocb *iocb, struct=20
>> iov_iter *iter,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 u64 start, u64 lockend,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct extent_state *cached_state,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 u64 disk_bytenr, u64 disk_io_size,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 size_t count, bool compressed,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct iovec *iov,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct io_uring_cmd *cmd)
>> +{
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_inode *inode =3D BTRFS_I(file_inode(ioc=
b->ki_filp));
>> +=C2=A0=C2=A0=C2=A0 struct extent_io_tree *io_tree =3D &inode->io_tree;
>> +=C2=A0=C2=A0=C2=A0 struct page **pages;
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_uring_priv *priv =3D NULL;
>> +=C2=A0=C2=A0=C2=A0 unsigned long nr_pages;
>> +=C2=A0=C2=A0=C2=A0 int ret;
>> +
>> +=C2=A0=C2=A0=C2=A0 nr_pages =3D DIV_ROUND_UP(disk_io_size, PAGE_SIZE);
>> +=C2=A0=C2=A0=C2=A0 pages =3D kcalloc(nr_pages, sizeof(struct page *), G=
FP_NOFS);
>> +=C2=A0=C2=A0=C2=A0 if (!pages)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -ENOMEM;
>> +=C2=A0=C2=A0=C2=A0 ret =3D btrfs_alloc_page_array(nr_pages, pages, 0);
>> +=C2=A0=C2=A0=C2=A0 if (ret) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D -ENOMEM;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto fail;
>> +=C2=A0=C2=A0=C2=A0 }
>> +
>> +=C2=A0=C2=A0=C2=A0 priv =3D kmalloc(sizeof(*priv), GFP_NOFS);
>> +=C2=A0=C2=A0=C2=A0 if (!priv) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D -ENOMEM;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto fail;
>> +=C2=A0=C2=A0=C2=A0 }
>> +
>> +=C2=A0=C2=A0=C2=A0 priv->iocb =3D *iocb;
>> +=C2=A0=C2=A0=C2=A0 priv->iov =3D iov;
>> +=C2=A0=C2=A0=C2=A0 priv->iter =3D *iter;
>> +=C2=A0=C2=A0=C2=A0 priv->count =3D count;
>> +=C2=A0=C2=A0=C2=A0 priv->cmd =3D cmd;
>> +=C2=A0=C2=A0=C2=A0 priv->cached_state =3D cached_state;
>> +=C2=A0=C2=A0=C2=A0 priv->compressed =3D compressed;
>> +=C2=A0=C2=A0=C2=A0 priv->nr_pages =3D nr_pages;
>> +=C2=A0=C2=A0=C2=A0 priv->pages =3D pages;
>> +=C2=A0=C2=A0=C2=A0 priv->start =3D start;
>> +=C2=A0=C2=A0=C2=A0 priv->lockend =3D lockend;
>> +=C2=A0=C2=A0=C2=A0 priv->err =3D 0;
>> +
>> +=C2=A0=C2=A0=C2=A0 ret =3D btrfs_encoded_read_regular_fill_pages(inode,=
 disk_bytenr,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 disk_io_size, pages,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 priv);
>> +=C2=A0=C2=A0=C2=A0 if (ret && ret !=3D -EIOCBQUEUED)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto fail;
>=20
> Turning both into return EIOCBQUEUED is a bit suspicious, but
> I lack context to say. Might make sense to return ret and let
> the caller handle it.

btrfs_encoded_read_regular_fill_pages returns 0 if the bio completes=20
before the function can finish, -EIOCBQUEUED otherwise. In either case=20
the behaviour of the calling function will be the same.

>> +
>> +=C2=A0=C2=A0=C2=A0 /*
>> +=C2=A0=C2=A0=C2=A0=C2=A0 * If we return -EIOCBQUEUED, we're deferring t=
he cleanup to
>> +=C2=A0=C2=A0=C2=A0=C2=A0 * btrfs_uring_read_finished, which will handle=
 unlocking the extent
>> +=C2=A0=C2=A0=C2=A0=C2=A0 * and inode and freeing the allocations.
>> +=C2=A0=C2=A0=C2=A0=C2=A0 */
>> +
>> +=C2=A0=C2=A0=C2=A0 return -EIOCBQUEUED;
>> +
>> +fail:
>> +=C2=A0=C2=A0=C2=A0 unlock_extent(io_tree, start, lockend, &cached_state=
);
>> +=C2=A0=C2=A0=C2=A0 btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
>> +=C2=A0=C2=A0=C2=A0 kfree(priv);
>> +=C2=A0=C2=A0=C2=A0 return ret;
>> +}
>> +
>> +static int btrfs_uring_encoded_read(struct io_uring_cmd *cmd,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unsigned int issue_flags)
>> +{
>> +=C2=A0=C2=A0=C2=A0 size_t copy_end_kernel =3D offsetofend(struct=20
>> btrfs_ioctl_encoded_io_args,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
 flags);
>> +=C2=A0=C2=A0=C2=A0 size_t copy_end;
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_ioctl_encoded_io_args args =3D { 0 };
>> +=C2=A0=C2=A0=C2=A0 int ret;
>> +=C2=A0=C2=A0=C2=A0 u64 disk_bytenr, disk_io_size;
>> +=C2=A0=C2=A0=C2=A0 struct file *file =3D cmd->file;
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_inode *inode =3D BTRFS_I(file->f_inode);
>> +=C2=A0=C2=A0=C2=A0 struct btrfs_fs_info *fs_info =3D inode->root->fs_in=
fo;
>> +=C2=A0=C2=A0=C2=A0 struct extent_io_tree *io_tree =3D &inode->io_tree;
>> +=C2=A0=C2=A0=C2=A0 struct iovec iovstack[UIO_FASTIOV];
>> +=C2=A0=C2=A0=C2=A0 struct iovec *iov =3D iovstack;
>> +=C2=A0=C2=A0=C2=A0 struct iov_iter iter;
>> +=C2=A0=C2=A0=C2=A0 loff_t pos;
>> +=C2=A0=C2=A0=C2=A0 struct kiocb kiocb;
>> +=C2=A0=C2=A0=C2=A0 struct extent_state *cached_state =3D NULL;
>> +=C2=A0=C2=A0=C2=A0 u64 start, lockend;
>> +=C2=A0=C2=A0=C2=A0 void __user *sqe_addr =3D u64_to_user_ptr(READ_ONCE(=
cmd->sqe->addr));
>=20
> Let's rename it, I was taken aback for a brief second why
> you're copy_from_user() from an SQE / the ring, which turns
> out to be a user pointer to a btrfs structure.

sqe_addr being the addr field in the SQE, not the address of the SQE. I=20
can see how it might be misleading, though.

> ...
>> +=C2=A0=C2=A0=C2=A0 ret =3D btrfs_encoded_read(&kiocb, &iter, &args, &ca=
ched_state,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 &disk_bytenr, &disk_io_size);
>> +=C2=A0=C2=A0=C2=A0 if (ret < 0 && ret !=3D -EIOCBQUEUED)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto out_free;
>> +
>> +=C2=A0=C2=A0=C2=A0 file_accessed(file);
>> +
>> +=C2=A0=C2=A0=C2=A0 if (copy_to_user(sqe_addr + copy_end, (char *)&args =
+=20
>> copy_end_kernel,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0 sizeof(args) - copy_end_kernel)) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (ret =3D=3D -EIOCBQUEUED)=
 {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 unlo=
ck_extent(io_tree, start, lockend, &cached_state);
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 btrf=
s_inode_unlock(inode, BTRFS_ILOCK_SHARED);
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D -EFAULT;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto out_free;
>=20
> It seems we're saving iov in the priv structure, who can access the iovec
> after the request is submitted? -EIOCBQUEUED in general means that the
> request is submitted and will get completed async, e.g. via callback, and
> if the bio callback can use the iov maybe via the iter, this goto will be
> a use after free.
>=20
> Also, you're returning -EFAULT back to io_uring, which will kill the
> io_uring request / cmd while there might still be in flight bios that
> can try to access it.
>=20
> Can you inject errors into the copy and test please?

The bio hasn't been submitted at this point, that happens in=20
btrfs_uring_read_extent. So far all we've done is read the metadata from=20
the page cache. The copy_to_user here is copying the metadata info to=20
the userspace structure.

>=20
>> +=C2=A0=C2=A0=C2=A0 }
>> +
>> +=C2=A0=C2=A0=C2=A0 if (ret =3D=3D -EIOCBQUEUED) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 u64 count;
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /*
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * If we've optimized t=
hings by storing the iovecs on the stack,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * undo this.
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */> +=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!iov) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 iov =
=3D kmalloc(sizeof(struct iovec) * args.iovcnt,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 GFP_NOFS);
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (=
!iov) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 unlock_extent(io_tree, start, lockend,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 &cached_state);
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 btrfs_inode_unlock(inode, BTRFS_ILOCK_SHARED);
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 ret =3D -ENOMEM;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 goto out_acct;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 memc=
py(iov, iovstack,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 sizeof(struct iovec) * args.iovcnt);
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 count =3D min_t(u64, iov_ite=
r_count(&iter), disk_io_size);
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Match ioctl by not return=
ing past EOF if uncompressed */
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (!args.compression)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 coun=
t =3D min_t(u64, count, args.len);
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ret =3D btrfs_uring_read_ext=
ent(&kiocb, &iter, start, lockend,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 cached_state, disk_bytenr,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 disk_io_size, count,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 args.compression, iov, cmd);
>> +
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto out_acct;
>> +=C2=A0=C2=A0=C2=A0 }
>> +
>> +out_free:
>> +=C2=A0=C2=A0=C2=A0 kfree(iov);
>> +
>> +out_acct:
>> +=C2=A0=C2=A0=C2=A0 if (ret > 0)
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 add_rchar(current, ret);
>> +=C2=A0=C2=A0=C2=A0 inc_syscr(current);
>> +
>> +=C2=A0=C2=A0=C2=A0 return ret;
>> +}
>=20