FETCH, COMMIT_AND_FETCH and NEED_GET_DATA publish the command in io->cmd before marking it cancelable. A cancel from the control path (STOP_DEV, QUIESCE_DEV) can complete it in between: issue path control-path cancel io->cmd = C take C, io_uring_cmd_done(C): C not marked, nothing to unlink ublk_prep_cancel(C) the completed C is linked on the cancelable list ring exit: the cancel walk hits it → GPF (KASAN, with a delay added) Mark the command before ublk_fill_io_cmd() publishes it. The handlers run with uring_lock held, as io_uring's cancel walk does, so marking takes no lock and the walk can't see a marked command before it is published. smp_wmb() orders the mark before the io->cmd store; the cancel loads cmd with READ_ONCE(io->cmd) before reading cmd->flags. A marked command has to be completed by io_uring_cmd_done(), so a failed FETCH and the inline UBLK_IO_RES_OK of NEED_GET_DATA now do that. The CQE is the same. Fixes: 216c8f5ef0f2 ("ublk: replace monitor with cancelable uring_cmd") Cc: stable@vger.kernel.org Signed-off-by: Ming Lei --- drivers/block/ublk_drv.c | 27 +++++++++++++++++++++------ 1 file changed, 21 insertions(+), 6 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 38ed7d0e3979..6015fb2fb925 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -2800,7 +2800,8 @@ static void ublk_cancel_cmd(struct ublk_queue *ubq, u16 tag, done = !!(io->flags & UBLK_IO_FLAG_CANCELED); if (!done) { io->flags |= UBLK_IO_FLAG_CANCELED; - cmd = io->cmd; + /* dependency ordered against smp_wmb() in ublk_prep_cancel() */ + cmd = READ_ONCE(io->cmd); io->cmd = NULL; } spin_unlock(&ubq->cancel_lock); @@ -3163,6 +3164,12 @@ ublk_fill_io_cmd(struct ublk_io *io, struct io_uring_cmd *cmd) return req; } +/* + * Call before ublk_fill_io_cmd() publishes @cmd in io->cmd: a control-path + * cancel may complete any command found there, and io_uring_cmd_done() only + * takes it off the cancelable list if it is marked already. The handlers + * hold uring_lock, so marking takes no lock. + */ static inline void ublk_prep_cancel(struct io_uring_cmd *cmd, unsigned int issue_flags, struct ublk_queue *ubq, u16 tag) @@ -3176,6 +3183,8 @@ static inline void ublk_prep_cancel(struct io_uring_cmd *cmd, pdu->ubq = ubq; pdu->tag = tag; io_uring_cmd_mark_cancelable(cmd, issue_flags); + /* pairs with the cancel loading cmd from io->cmd, then cmd->flags */ + smp_wmb(); } static void ublk_io_release(void *priv) @@ -3423,11 +3432,11 @@ static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd, ret = ublk_check_fetch_buf(ub, addr); if (ret) goto out; + /* before ublk_fetch() publishes io->cmd, see ublk_prep_cancel() */ + ublk_prep_cancel(cmd, issue_flags, ubq, tag); ret = ublk_fetch(cmd, ub, io, addr, q_id); if (ret) - goto out; - - ublk_prep_cancel(cmd, issue_flags, ubq, tag); + goto out_done; return -EIOCBQUEUED; } @@ -3471,6 +3480,7 @@ static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd, if (ret) goto out; io->res = result; + ublk_prep_cancel(cmd, issue_flags, ubq, tag); req = ublk_fill_io_cmd(io, cmd); ublk_apply_io_buf(ub, io, cmd, addr, &auto_buf, &buf_idx); if (buf_idx != UBLK_INVALID_BUF_IDX) @@ -3489,19 +3499,24 @@ static int ublk_ch_uring_cmd_local(struct io_uring_cmd *cmd, * uring_cmd active first and prepare for handling new requeued * request */ + ublk_prep_cancel(cmd, issue_flags, ubq, tag); req = ublk_fill_io_cmd(io, cmd); io->buf.addr = addr; if (likely(ublk_get_data(ubq, io, req))) { __ublk_prep_compl_io_cmd(io, req); - return UBLK_IO_RES_OK; + ret = UBLK_IO_RES_OK; + goto out_done; } break; default: goto out; } - ublk_prep_cancel(cmd, issue_flags, ubq, tag); return -EIOCBQUEUED; + out_done: + /* marked cancelable: complete through io_uring_cmd_done() */ + io_uring_cmd_done(cmd, ret, issue_flags); + return -EIOCBQUEUED; out: pr_devel("%s: complete: cmd op %d, tag %d ret %x io_flags %x\n", __func__, cmd_op, tag, ret, io ? io->flags : 0); -- 2.55.0