https://github.com/torvalds/linux
Tip revision: e5fa841af679cb830da6c609c740a37bdc0b8b35 authored by Linus Torvalds on 17 August 2024, 00:08:02 UTC
Merge tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Merge tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Tip revision: e5fa841
kbuf.c
// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/vmalloc.h>
#include <linux/io_uring.h>
#include <uapi/linux/io_uring.h>
#include "io_uring.h"
#include "opdef.h"
#include "kbuf.h"
#include "memmap.h"
/* BIDs are addressed by a 16-bit field in a CQE */
#define MAX_BIDS_PER_BGID (1 << 16)
struct kmem_cache *io_buf_cachep;
struct io_provide_buf {
struct file *file;
__u64 addr;
__u32 len;
__u32 bgid;
__u32 nbufs;
__u16 bid;
};
static inline struct io_buffer_list *io_buffer_get_list(struct io_ring_ctx *ctx,
unsigned int bgid)
{
lockdep_assert_held(&ctx->uring_lock);
return xa_load(&ctx->io_bl_xa, bgid);
}
static int io_buffer_add_list(struct io_ring_ctx *ctx,
struct io_buffer_list *bl, unsigned int bgid)
{
/*
* Store buffer group ID and finally mark the list as visible.
* The normal lookup doesn't care about the visibility as we're
* always under the ->uring_lock, but the RCU lookup from mmap does.
*/
bl->bgid = bgid;
atomic_set(&bl->refs, 1);
return xa_err(xa_store(&ctx->io_bl_xa, bgid, bl, GFP_KERNEL));
}
bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_buffer_list *bl;
struct io_buffer *buf;
io_ring_submit_lock(ctx, issue_flags);
buf = req->kbuf;
bl = io_buffer_get_list(ctx, buf->bgid);
list_add(&buf->list, &bl->buf_list);
req->flags &= ~REQ_F_BUFFER_SELECTED;
req->buf_index = buf->bgid;
io_ring_submit_unlock(ctx, issue_flags);
return true;
}
void __io_put_kbuf(struct io_kiocb *req, unsigned issue_flags)
{
/*
* We can add this buffer back to two lists:
*
* 1) The io_buffers_cache list. This one is protected by the
* ctx->uring_lock. If we already hold this lock, add back to this
* list as we can grab it from issue as well.
* 2) The io_buffers_comp list. This one is protected by the
* ctx->completion_lock.
*
* We migrate buffers from the comp_list to the issue cache list
* when we need one.
*/
if (issue_flags & IO_URING_F_UNLOCKED) {
struct io_ring_ctx *ctx = req->ctx;
spin_lock(&ctx->completion_lock);
__io_put_kbuf_list(req, &ctx->io_buffers_comp);
spin_unlock(&ctx->completion_lock);
} else {
lockdep_assert_held(&req->ctx->uring_lock);
__io_put_kbuf_list(req, &req->ctx->io_buffers_cache);
}
}
static void __user *io_provided_buffer_select(struct io_kiocb *req, size_t *len,
struct io_buffer_list *bl)
{
if (!list_empty(&bl->buf_list)) {
struct io_buffer *kbuf;
kbuf = list_first_entry(&bl->buf_list, struct io_buffer, list);
list_del(&kbuf->list);
if (*len == 0 || *len > kbuf->len)
*len = kbuf->len;
if (list_empty(&bl->buf_list))
req->flags |= REQ_F_BL_EMPTY;
req->flags |= REQ_F_BUFFER_SELECTED;
req->kbuf = kbuf;
req->buf_index = kbuf->bid;
return u64_to_user_ptr(kbuf->addr);
}
return NULL;
}
static int io_provided_buffers_select(struct io_kiocb *req, size_t *len,
struct io_buffer_list *bl,
struct iovec *iov)
{
void __user *buf;
buf = io_provided_buffer_select(req, len, bl);
if (unlikely(!buf))
return -ENOBUFS;
iov[0].iov_base = buf;
iov[0].iov_len = *len;
return 0;
}
static struct io_uring_buf *io_ring_head_to_buf(struct io_uring_buf_ring *br,
__u16 head, __u16 mask)
{
return &br->bufs[head & mask];
}
static void __user *io_ring_buffer_select(struct io_kiocb *req, size_t *len,
struct io_buffer_list *bl,
unsigned int issue_flags)
{
struct io_uring_buf_ring *br = bl->buf_ring;
__u16 tail, head = bl->head;
struct io_uring_buf *buf;
tail = smp_load_acquire(&br->tail);
if (unlikely(tail == head))
return NULL;
if (head + 1 == tail)
req->flags |= REQ_F_BL_EMPTY;
buf = io_ring_head_to_buf(br, head, bl->mask);
if (*len == 0 || *len > buf->len)
*len = buf->len;
req->flags |= REQ_F_BUFFER_RING | REQ_F_BUFFERS_COMMIT;
req->buf_list = bl;
req->buf_index = buf->bid;
if (issue_flags & IO_URING_F_UNLOCKED || !io_file_can_poll(req)) {
/*
* If we came in unlocked, we have no choice but to consume the
* buffer here, otherwise nothing ensures that the buffer won't
* get used by others. This does mean it'll be pinned until the
* IO completes, coming in unlocked means we're being called from
* io-wq context and there may be further retries in async hybrid
* mode. For the locked case, the caller must call commit when
* the transfer completes (or if we get -EAGAIN and must poll of
* retry).
*/
req->flags &= ~REQ_F_BUFFERS_COMMIT;
req->buf_list = NULL;
bl->head++;
}
return u64_to_user_ptr(buf->addr);
}
void __user *io_buffer_select(struct io_kiocb *req, size_t *len,
unsigned int issue_flags)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_buffer_list *bl;
void __user *ret = NULL;
io_ring_submit_lock(req->ctx, issue_flags);
bl = io_buffer_get_list(ctx, req->buf_index);
if (likely(bl)) {
if (bl->is_buf_ring)
ret = io_ring_buffer_select(req, len, bl, issue_flags);
else
ret = io_provided_buffer_select(req, len, bl);
}
io_ring_submit_unlock(req->ctx, issue_flags);
return ret;
}
/* cap it at a reasonable 256, will be one page even for 4K */
#define PEEK_MAX_IMPORT 256
static int io_ring_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg,
struct io_buffer_list *bl)
{
struct io_uring_buf_ring *br = bl->buf_ring;
struct iovec *iov = arg->iovs;
int nr_iovs = arg->nr_iovs;
__u16 nr_avail, tail, head;
struct io_uring_buf *buf;
tail = smp_load_acquire(&br->tail);
head = bl->head;
nr_avail = min_t(__u16, tail - head, UIO_MAXIOV);
if (unlikely(!nr_avail))
return -ENOBUFS;
buf = io_ring_head_to_buf(br, head, bl->mask);
if (arg->max_len) {
int needed;
needed = (arg->max_len + buf->len - 1) / buf->len;
needed = min(needed, PEEK_MAX_IMPORT);
if (nr_avail > needed)
nr_avail = needed;
}
/*
* only alloc a bigger array if we know we have data to map, eg not
* a speculative peek operation.
*/
if (arg->mode & KBUF_MODE_EXPAND && nr_avail > nr_iovs && arg->max_len) {
iov = kmalloc_array(nr_avail, sizeof(struct iovec), GFP_KERNEL);
if (unlikely(!iov))
return -ENOMEM;
if (arg->mode & KBUF_MODE_FREE)
kfree(arg->iovs);
arg->iovs = iov;
nr_iovs = nr_avail;
} else if (nr_avail < nr_iovs) {
nr_iovs = nr_avail;
}
/* set it to max, if not set, so we can use it unconditionally */
if (!arg->max_len)
arg->max_len = INT_MAX;
req->buf_index = buf->bid;
do {
/* truncate end piece, if needed */
if (buf->len > arg->max_len)
buf->len = arg->max_len;
iov->iov_base = u64_to_user_ptr(buf->addr);
iov->iov_len = buf->len;
iov++;
arg->out_len += buf->len;
arg->max_len -= buf->len;
if (!arg->max_len)
break;
buf = io_ring_head_to_buf(br, ++head, bl->mask);
} while (--nr_iovs);
if (head == tail)
req->flags |= REQ_F_BL_EMPTY;
req->flags |= REQ_F_BUFFER_RING;
req->buf_list = bl;
return iov - arg->iovs;
}
int io_buffers_select(struct io_kiocb *req, struct buf_sel_arg *arg,
unsigned int issue_flags)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_buffer_list *bl;
int ret = -ENOENT;
io_ring_submit_lock(ctx, issue_flags);
bl = io_buffer_get_list(ctx, req->buf_index);
if (unlikely(!bl))
goto out_unlock;
if (bl->is_buf_ring) {
ret = io_ring_buffers_peek(req, arg, bl);
/*
* Don't recycle these buffers if we need to go through poll.
* Nobody else can use them anyway, and holding on to provided
* buffers for a send/write operation would happen on the app
* side anyway with normal buffers. Besides, we already
* committed them, they cannot be put back in the queue.
*/
if (ret > 0) {
req->flags |= REQ_F_BL_NO_RECYCLE;
req->buf_list->head += ret;
}
} else {
ret = io_provided_buffers_select(req, &arg->out_len, bl, arg->iovs);
}
out_unlock:
io_ring_submit_unlock(ctx, issue_flags);
return ret;
}
int io_buffers_peek(struct io_kiocb *req, struct buf_sel_arg *arg)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_buffer_list *bl;
int ret;
lockdep_assert_held(&ctx->uring_lock);
bl = io_buffer_get_list(ctx, req->buf_index);
if (unlikely(!bl))
return -ENOENT;
if (bl->is_buf_ring) {
ret = io_ring_buffers_peek(req, arg, bl);
if (ret > 0)
req->flags |= REQ_F_BUFFERS_COMMIT;
return ret;
}
/* don't support multiple buffer selections for legacy */
return io_provided_buffers_select(req, &arg->max_len, bl, arg->iovs);
}
static int __io_remove_buffers(struct io_ring_ctx *ctx,
struct io_buffer_list *bl, unsigned nbufs)
{
unsigned i = 0;
/* shouldn't happen */
if (!nbufs)
return 0;
if (bl->is_buf_ring) {
i = bl->buf_ring->tail - bl->head;
if (bl->buf_nr_pages) {
int j;
if (!bl->is_mmap) {
for (j = 0; j < bl->buf_nr_pages; j++)
unpin_user_page(bl->buf_pages[j]);
}
io_pages_unmap(bl->buf_ring, &bl->buf_pages,
&bl->buf_nr_pages, bl->is_mmap);
bl->is_mmap = 0;
}
/* make sure it's seen as empty */
INIT_LIST_HEAD(&bl->buf_list);
bl->is_buf_ring = 0;
return i;
}
/* protects io_buffers_cache */
lockdep_assert_held(&ctx->uring_lock);
while (!list_empty(&bl->buf_list)) {
struct io_buffer *nxt;
nxt = list_first_entry(&bl->buf_list, struct io_buffer, list);
list_move(&nxt->list, &ctx->io_buffers_cache);
if (++i == nbufs)
return i;
cond_resched();
}
return i;
}
void io_put_bl(struct io_ring_ctx *ctx, struct io_buffer_list *bl)
{
if (atomic_dec_and_test(&bl->refs)) {
__io_remove_buffers(ctx, bl, -1U);
kfree_rcu(bl, rcu);
}
}
void io_destroy_buffers(struct io_ring_ctx *ctx)
{
struct io_buffer_list *bl;
struct list_head *item, *tmp;
struct io_buffer *buf;
unsigned long index;
xa_for_each(&ctx->io_bl_xa, index, bl) {
xa_erase(&ctx->io_bl_xa, bl->bgid);
io_put_bl(ctx, bl);
}
/*
* Move deferred locked entries to cache before pruning
*/
spin_lock(&ctx->completion_lock);
if (!list_empty(&ctx->io_buffers_comp))
list_splice_init(&ctx->io_buffers_comp, &ctx->io_buffers_cache);
spin_unlock(&ctx->completion_lock);
list_for_each_safe(item, tmp, &ctx->io_buffers_cache) {
buf = list_entry(item, struct io_buffer, list);
kmem_cache_free(io_buf_cachep, buf);
}
}
int io_remove_buffers_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
struct io_provide_buf *p = io_kiocb_to_cmd(req, struct io_provide_buf);
u64 tmp;
if (sqe->rw_flags || sqe->addr || sqe->len || sqe->off ||
sqe->splice_fd_in)
return -EINVAL;
tmp = READ_ONCE(sqe->fd);
if (!tmp || tmp > MAX_BIDS_PER_BGID)
return -EINVAL;
memset(p, 0, sizeof(*p));
p->nbufs = tmp;
p->bgid = READ_ONCE(sqe->buf_group);
return 0;
}
int io_remove_buffers(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_provide_buf *p = io_kiocb_to_cmd(req, struct io_provide_buf);
struct io_ring_ctx *ctx = req->ctx;
struct io_buffer_list *bl;
int ret = 0;
io_ring_submit_lock(ctx, issue_flags);
ret = -ENOENT;
bl = io_buffer_get_list(ctx, p->bgid);
if (bl) {
ret = -EINVAL;
/* can't use provide/remove buffers command on mapped buffers */
if (!bl->is_buf_ring)
ret = __io_remove_buffers(ctx, bl, p->nbufs);
}
io_ring_submit_unlock(ctx, issue_flags);
if (ret < 0)
req_set_fail(req);
io_req_set_res(req, ret, 0);
return IOU_OK;
}
int io_provide_buffers_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
unsigned long size, tmp_check;
struct io_provide_buf *p = io_kiocb_to_cmd(req, struct io_provide_buf);
u64 tmp;
if (sqe->rw_flags || sqe->splice_fd_in)
return -EINVAL;
tmp = READ_ONCE(sqe->fd);
if (!tmp || tmp > MAX_BIDS_PER_BGID)
return -E2BIG;
p->nbufs = tmp;
p->addr = READ_ONCE(sqe->addr);
p->len = READ_ONCE(sqe->len);
if (check_mul_overflow((unsigned long)p->len, (unsigned long)p->nbufs,
&size))
return -EOVERFLOW;
if (check_add_overflow((unsigned long)p->addr, size, &tmp_check))
return -EOVERFLOW;
size = (unsigned long)p->len * p->nbufs;
if (!access_ok(u64_to_user_ptr(p->addr), size))
return -EFAULT;
p->bgid = READ_ONCE(sqe->buf_group);
tmp = READ_ONCE(sqe->off);
if (tmp > USHRT_MAX)
return -E2BIG;
if (tmp + p->nbufs > MAX_BIDS_PER_BGID)
return -EINVAL;
p->bid = tmp;
return 0;
}
#define IO_BUFFER_ALLOC_BATCH 64
static int io_refill_buffer_cache(struct io_ring_ctx *ctx)
{
struct io_buffer *bufs[IO_BUFFER_ALLOC_BATCH];
int allocated;
/*
* Completions that don't happen inline (eg not under uring_lock) will
* add to ->io_buffers_comp. If we don't have any free buffers, check
* the completion list and splice those entries first.
*/
if (!list_empty_careful(&ctx->io_buffers_comp)) {
spin_lock(&ctx->completion_lock);
if (!list_empty(&ctx->io_buffers_comp)) {
list_splice_init(&ctx->io_buffers_comp,
&ctx->io_buffers_cache);
spin_unlock(&ctx->completion_lock);
return 0;
}
spin_unlock(&ctx->completion_lock);
}
/*
* No free buffers and no completion entries either. Allocate a new
* batch of buffer entries and add those to our freelist.
*/
allocated = kmem_cache_alloc_bulk(io_buf_cachep, GFP_KERNEL_ACCOUNT,
ARRAY_SIZE(bufs), (void **) bufs);
if (unlikely(!allocated)) {
/*
* Bulk alloc is all-or-nothing. If we fail to get a batch,
* retry single alloc to be on the safe side.
*/
bufs[0] = kmem_cache_alloc(io_buf_cachep, GFP_KERNEL);
if (!bufs[0])
return -ENOMEM;
allocated = 1;
}
while (allocated)
list_add_tail(&bufs[--allocated]->list, &ctx->io_buffers_cache);
return 0;
}
static int io_add_buffers(struct io_ring_ctx *ctx, struct io_provide_buf *pbuf,
struct io_buffer_list *bl)
{
struct io_buffer *buf;
u64 addr = pbuf->addr;
int i, bid = pbuf->bid;
for (i = 0; i < pbuf->nbufs; i++) {
if (list_empty(&ctx->io_buffers_cache) &&
io_refill_buffer_cache(ctx))
break;
buf = list_first_entry(&ctx->io_buffers_cache, struct io_buffer,
list);
list_move_tail(&buf->list, &bl->buf_list);
buf->addr = addr;
buf->len = min_t(__u32, pbuf->len, MAX_RW_COUNT);
buf->bid = bid;
buf->bgid = pbuf->bgid;
addr += pbuf->len;
bid++;
cond_resched();
}
return i ? 0 : -ENOMEM;
}
int io_provide_buffers(struct io_kiocb *req, unsigned int issue_flags)
{
struct io_provide_buf *p = io_kiocb_to_cmd(req, struct io_provide_buf);
struct io_ring_ctx *ctx = req->ctx;
struct io_buffer_list *bl;
int ret = 0;
io_ring_submit_lock(ctx, issue_flags);
bl = io_buffer_get_list(ctx, p->bgid);
if (unlikely(!bl)) {
bl = kzalloc(sizeof(*bl), GFP_KERNEL_ACCOUNT);
if (!bl) {
ret = -ENOMEM;
goto err;
}
INIT_LIST_HEAD(&bl->buf_list);
ret = io_buffer_add_list(ctx, bl, p->bgid);
if (ret) {
/*
* Doesn't need rcu free as it was never visible, but
* let's keep it consistent throughout.
*/
kfree_rcu(bl, rcu);
goto err;
}
}
/* can't add buffers via this command for a mapped buffer ring */
if (bl->is_buf_ring) {
ret = -EINVAL;
goto err;
}
ret = io_add_buffers(ctx, p, bl);
err:
io_ring_submit_unlock(ctx, issue_flags);
if (ret < 0)
req_set_fail(req);
io_req_set_res(req, ret, 0);
return IOU_OK;
}
static int io_pin_pbuf_ring(struct io_uring_buf_reg *reg,
struct io_buffer_list *bl)
{
struct io_uring_buf_ring *br = NULL;
struct page **pages;
int nr_pages, ret;
pages = io_pin_pages(reg->ring_addr,
flex_array_size(br, bufs, reg->ring_entries),
&nr_pages);
if (IS_ERR(pages))
return PTR_ERR(pages);
br = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
if (!br) {
ret = -ENOMEM;
goto error_unpin;
}
#ifdef SHM_COLOUR
/*
* On platforms that have specific aliasing requirements, SHM_COLOUR
* is set and we must guarantee that the kernel and user side align
* nicely. We cannot do that if IOU_PBUF_RING_MMAP isn't set and
* the application mmap's the provided ring buffer. Fail the request
* if we, by chance, don't end up with aligned addresses. The app
* should use IOU_PBUF_RING_MMAP instead, and liburing will handle
* this transparently.
*/
if ((reg->ring_addr | (unsigned long) br) & (SHM_COLOUR - 1)) {
ret = -EINVAL;
goto error_unpin;
}
#endif
bl->buf_pages = pages;
bl->buf_nr_pages = nr_pages;
bl->buf_ring = br;
bl->is_buf_ring = 1;
bl->is_mmap = 0;
return 0;
error_unpin:
unpin_user_pages(pages, nr_pages);
kvfree(pages);
vunmap(br);
return ret;
}
static int io_alloc_pbuf_ring(struct io_ring_ctx *ctx,
struct io_uring_buf_reg *reg,
struct io_buffer_list *bl)
{
size_t ring_size;
ring_size = reg->ring_entries * sizeof(struct io_uring_buf_ring);
bl->buf_ring = io_pages_map(&bl->buf_pages, &bl->buf_nr_pages, ring_size);
if (IS_ERR(bl->buf_ring)) {
bl->buf_ring = NULL;
return -ENOMEM;
}
bl->is_buf_ring = 1;
bl->is_mmap = 1;
return 0;
}
int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
{
struct io_uring_buf_reg reg;
struct io_buffer_list *bl, *free_bl = NULL;
int ret;
lockdep_assert_held(&ctx->uring_lock);
if (copy_from_user(®, arg, sizeof(reg)))
return -EFAULT;
if (reg.resv[0] || reg.resv[1] || reg.resv[2])
return -EINVAL;
if (reg.flags & ~IOU_PBUF_RING_MMAP)
return -EINVAL;
if (!(reg.flags & IOU_PBUF_RING_MMAP)) {
if (!reg.ring_addr)
return -EFAULT;
if (reg.ring_addr & ~PAGE_MASK)
return -EINVAL;
} else {
if (reg.ring_addr)
return -EINVAL;
}
if (!is_power_of_2(reg.ring_entries))
return -EINVAL;
/* cannot disambiguate full vs empty due to head/tail size */
if (reg.ring_entries >= 65536)
return -EINVAL;
bl = io_buffer_get_list(ctx, reg.bgid);
if (bl) {
/* if mapped buffer ring OR classic exists, don't allow */
if (bl->is_buf_ring || !list_empty(&bl->buf_list))
return -EEXIST;
} else {
free_bl = bl = kzalloc(sizeof(*bl), GFP_KERNEL);
if (!bl)
return -ENOMEM;
}
if (!(reg.flags & IOU_PBUF_RING_MMAP))
ret = io_pin_pbuf_ring(®, bl);
else
ret = io_alloc_pbuf_ring(ctx, ®, bl);
if (!ret) {
bl->nr_entries = reg.ring_entries;
bl->mask = reg.ring_entries - 1;
io_buffer_add_list(ctx, bl, reg.bgid);
return 0;
}
kfree_rcu(free_bl, rcu);
return ret;
}
int io_unregister_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
{
struct io_uring_buf_reg reg;
struct io_buffer_list *bl;
lockdep_assert_held(&ctx->uring_lock);
if (copy_from_user(®, arg, sizeof(reg)))
return -EFAULT;
if (reg.resv[0] || reg.resv[1] || reg.resv[2])
return -EINVAL;
if (reg.flags)
return -EINVAL;
bl = io_buffer_get_list(ctx, reg.bgid);
if (!bl)
return -ENOENT;
if (!bl->is_buf_ring)
return -EINVAL;
xa_erase(&ctx->io_bl_xa, bl->bgid);
io_put_bl(ctx, bl);
return 0;
}
int io_register_pbuf_status(struct io_ring_ctx *ctx, void __user *arg)
{
struct io_uring_buf_status buf_status;
struct io_buffer_list *bl;
int i;
if (copy_from_user(&buf_status, arg, sizeof(buf_status)))
return -EFAULT;
for (i = 0; i < ARRAY_SIZE(buf_status.resv); i++)
if (buf_status.resv[i])
return -EINVAL;
bl = io_buffer_get_list(ctx, buf_status.buf_group);
if (!bl)
return -ENOENT;
if (!bl->is_buf_ring)
return -EINVAL;
buf_status.head = bl->head;
if (copy_to_user(arg, &buf_status, sizeof(buf_status)))
return -EFAULT;
return 0;
}
struct io_buffer_list *io_pbuf_get_bl(struct io_ring_ctx *ctx,
unsigned long bgid)
{
struct io_buffer_list *bl;
bool ret;
/*
* We have to be a bit careful here - we're inside mmap and cannot grab
* the uring_lock. This means the buffer_list could be simultaneously
* going away, if someone is trying to be sneaky. Look it up under rcu
* so we know it's not going away, and attempt to grab a reference to
* it. If the ref is already zero, then fail the mapping. If successful,
* the caller will call io_put_bl() to drop the the reference at at the
* end. This may then safely free the buffer_list (and drop the pages)
* at that point, vm_insert_pages() would've already grabbed the
* necessary vma references.
*/
rcu_read_lock();
bl = xa_load(&ctx->io_bl_xa, bgid);
/* must be a mmap'able buffer ring and have pages */
ret = false;
if (bl && bl->is_mmap)
ret = atomic_inc_not_zero(&bl->refs);
rcu_read_unlock();
if (ret)
return bl;
return ERR_PTR(-EINVAL);
}
int io_pbuf_mmap(struct file *file, struct vm_area_struct *vma)
{
struct io_ring_ctx *ctx = file->private_data;
loff_t pgoff = vma->vm_pgoff << PAGE_SHIFT;
struct io_buffer_list *bl;
int bgid, ret;
bgid = (pgoff & ~IORING_OFF_MMAP_MASK) >> IORING_OFF_PBUF_SHIFT;
bl = io_pbuf_get_bl(ctx, bgid);
if (IS_ERR(bl))
return PTR_ERR(bl);
ret = io_uring_mmap_pages(ctx, vma, bl->buf_pages, bl->buf_nr_pages);
io_put_bl(ctx, bl);
return ret;
}