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io_uring: fix up O_NONBLOCK handling for sockets
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We've got two issues with the non-regular file handling for non-blocking
IO:

1) We don't want to re-do a short read in full for a non-regular file,
   as we can't just read the data again.
2) For non-regular files that don't support non-blocking IO attempts,
   we need to punt to async context even if the file is opened as
   non-blocking. Otherwise the caller always gets -EAGAIN.

Add two new request flags to handle these cases. One is just a cache
of the inode S_ISREG() status, the other tells io_uring that we always
need to punt this request to async context, even if REQ_F_NOWAIT is set.

Cc: stable@vger.kernel.org
Reported-by: Hrvoje Zeba <zeba.hrvoje@gmail.com>
Tested-by: Hrvoje Zeba <zeba.hrvoje@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Jens Axboe committed Oct 17, 2019
1 parent 6333ff6 commit 491381c
Showing 1 changed file with 39 additions and 18 deletions.
57 changes: 39 additions & 18 deletions fs/io_uring.c
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Original file line number Diff line number Diff line change
Expand Up @@ -322,6 +322,8 @@ struct io_kiocb {
#define REQ_F_FAIL_LINK 256 /* fail rest of links */
#define REQ_F_SHADOW_DRAIN 512 /* link-drain shadow req */
#define REQ_F_TIMEOUT 1024 /* timeout request */
#define REQ_F_ISREG 2048 /* regular file */
#define REQ_F_MUST_PUNT 4096 /* must be punted even for NONBLOCK */
u64 user_data;
u32 result;
u32 sequence;
Expand Down Expand Up @@ -914,26 +916,26 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
return ret;
}

static void kiocb_end_write(struct kiocb *kiocb)
static void kiocb_end_write(struct io_kiocb *req)
{
if (kiocb->ki_flags & IOCB_WRITE) {
struct inode *inode = file_inode(kiocb->ki_filp);
/*
* Tell lockdep we inherited freeze protection from submission
* thread.
*/
if (req->flags & REQ_F_ISREG) {
struct inode *inode = file_inode(req->file);

/*
* Tell lockdep we inherited freeze protection from submission
* thread.
*/
if (S_ISREG(inode->i_mode))
__sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
file_end_write(kiocb->ki_filp);
__sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
}
file_end_write(req->file);
}

static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
{
struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);

kiocb_end_write(kiocb);
if (kiocb->ki_flags & IOCB_WRITE)
kiocb_end_write(req);

if ((req->flags & REQ_F_LINK) && res != req->result)
req->flags |= REQ_F_FAIL_LINK;
Expand All @@ -945,7 +947,8 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
{
struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);

kiocb_end_write(kiocb);
if (kiocb->ki_flags & IOCB_WRITE)
kiocb_end_write(req);

if ((req->flags & REQ_F_LINK) && res != req->result)
req->flags |= REQ_F_FAIL_LINK;
Expand Down Expand Up @@ -1059,8 +1062,17 @@ static int io_prep_rw(struct io_kiocb *req, const struct sqe_submit *s,
if (!req->file)
return -EBADF;

if (force_nonblock && !io_file_supports_async(req->file))
force_nonblock = false;
if (S_ISREG(file_inode(req->file)->i_mode))
req->flags |= REQ_F_ISREG;

/*
* If the file doesn't support async, mark it as REQ_F_MUST_PUNT so
* we know to async punt it even if it was opened O_NONBLOCK
*/
if (force_nonblock && !io_file_supports_async(req->file)) {
req->flags |= REQ_F_MUST_PUNT;
return -EAGAIN;
}

kiocb->ki_pos = READ_ONCE(sqe->off);
kiocb->ki_flags = iocb_flags(kiocb->ki_filp);
Expand All @@ -1081,7 +1093,8 @@ static int io_prep_rw(struct io_kiocb *req, const struct sqe_submit *s,
return ret;

/* don't allow async punt if RWF_NOWAIT was requested */
if (kiocb->ki_flags & IOCB_NOWAIT)
if ((kiocb->ki_flags & IOCB_NOWAIT) ||
(req->file->f_flags & O_NONBLOCK))
req->flags |= REQ_F_NOWAIT;

if (force_nonblock)
Expand Down Expand Up @@ -1382,7 +1395,9 @@ static int io_read(struct io_kiocb *req, const struct sqe_submit *s,
* need async punt anyway, so it's more efficient to do it
* here.
*/
if (force_nonblock && ret2 > 0 && ret2 < read_size)
if (force_nonblock && !(req->flags & REQ_F_NOWAIT) &&
(req->flags & REQ_F_ISREG) &&
ret2 > 0 && ret2 < read_size)
ret2 = -EAGAIN;
/* Catch -EAGAIN return for forced non-blocking submission */
if (!force_nonblock || ret2 != -EAGAIN) {
Expand Down Expand Up @@ -1447,7 +1462,7 @@ static int io_write(struct io_kiocb *req, const struct sqe_submit *s,
* released so that it doesn't complain about the held lock when
* we return to userspace.
*/
if (S_ISREG(file_inode(file)->i_mode)) {
if (req->flags & REQ_F_ISREG) {
__sb_start_write(file_inode(file)->i_sb,
SB_FREEZE_WRITE, true);
__sb_writers_release(file_inode(file)->i_sb,
Expand Down Expand Up @@ -2282,7 +2297,13 @@ static int __io_queue_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
int ret;

ret = __io_submit_sqe(ctx, req, s, force_nonblock);
if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) {

/*
* We async punt it if the file wasn't marked NOWAIT, or if the file
* doesn't support non-blocking read/write attempts
*/
if (ret == -EAGAIN && (!(req->flags & REQ_F_NOWAIT) ||
(req->flags & REQ_F_MUST_PUNT))) {
struct io_uring_sqe *sqe_copy;

sqe_copy = kmemdup(s->sqe, sizeof(*sqe_copy), GFP_KERNEL);
Expand Down

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