Commit 33f2a757 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Kevin Wolf
Browse files

block: add BlockBackend->in_flight counter 



BlockBackend currently relies on BlockDriverState->in_flight to track
requests for blk_drain().  There is a corner case where
BlockDriverState->in_flight cannot be used though: blk->root can be NULL
when there is no medium.  This results in a segfault when the NULL
pointer is dereferenced.

Introduce a BlockBackend->in_flight counter for aio requests so it works
even when blk->root == NULL.

Based on a patch by Kevin Wolf <kwolf@redhat.com>.

Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 7719f3c9

block.c

+1 −1
Original line number Diff line number Diff line
@@ -4713,7 +4713,7 @@ out: 


AioContext *bdrv_get_aio_context(BlockDriverState *bs)

{

    return bs->aio_context;

    return bs ? bs->aio_context : qemu_get_aio_context();

}



AioWait *bdrv_get_aio_wait(BlockDriverState *bs)

block/block-backend.c

+53 −7
Original line number Diff line number Diff line
@@ -73,6 +73,14 @@ struct BlockBackend { 
    int quiesce_counter;

    VMChangeStateEntry *vmsh;

    bool force_allow_inactivate;



    /* Number of in-flight aio requests.  BlockDriverState also counts

     * in-flight requests but aio requests can exist even when blk->root is

     * NULL, so we cannot rely on its counter for that case.

     * Accessed with atomic ops.

     */

    unsigned int in_flight;

    AioWait wait;

};



typedef struct BlockBackendAIOCB {
@@ -1225,11 +1233,22 @@ int blk_make_zero(BlockBackend *blk, BdrvRequestFlags flags) 
    return bdrv_make_zero(blk->root, flags);

}



static void blk_inc_in_flight(BlockBackend *blk)

{

    atomic_inc(&blk->in_flight);

}



static void blk_dec_in_flight(BlockBackend *blk)

{

    atomic_dec(&blk->in_flight);

    aio_wait_kick(&blk->wait);

}



static void error_callback_bh(void *opaque)

{

    struct BlockBackendAIOCB *acb = opaque;



    bdrv_dec_in_flight(acb->common.bs);

    blk_dec_in_flight(acb->blk);

    acb->common.cb(acb->common.opaque, acb->ret);

    qemu_aio_unref(acb);

}
@@ -1240,7 +1259,7 @@ BlockAIOCB *blk_abort_aio_request(BlockBackend *blk, 
{

    struct BlockBackendAIOCB *acb;



    bdrv_inc_in_flight(blk_bs(blk));

    blk_inc_in_flight(blk);

    acb = blk_aio_get(&block_backend_aiocb_info, blk, cb, opaque);

    acb->blk = blk;

    acb->ret = ret;
@@ -1263,7 +1282,7 @@ static const AIOCBInfo blk_aio_em_aiocb_info = { 
static void blk_aio_complete(BlkAioEmAIOCB *acb)

{

    if (acb->has_returned) {

        bdrv_dec_in_flight(acb->common.bs);

        blk_dec_in_flight(acb->rwco.blk);

        acb->common.cb(acb->common.opaque, acb->rwco.ret);

        qemu_aio_unref(acb);

    }
@@ -1284,7 +1303,7 @@ static BlockAIOCB *blk_aio_prwv(BlockBackend *blk, int64_t offset, int bytes, 
    BlkAioEmAIOCB *acb;

    Coroutine *co;



    bdrv_inc_in_flight(blk_bs(blk));

    blk_inc_in_flight(blk);

    acb = blk_aio_get(&blk_aio_em_aiocb_info, blk, cb, opaque);

    acb->rwco = (BlkRwCo) {

        .blk    = blk,
@@ -1521,14 +1540,41 @@ int blk_flush(BlockBackend *blk) 


void blk_drain(BlockBackend *blk)

{

    if (blk_bs(blk)) {

        bdrv_drain(blk_bs(blk));

    BlockDriverState *bs = blk_bs(blk);



    if (bs) {

        bdrv_drained_begin(bs);

    }



    /* We may have -ENOMEDIUM completions in flight */

    AIO_WAIT_WHILE(&blk->wait,

            blk_get_aio_context(blk),

            atomic_mb_read(&blk->in_flight) > 0);



    if (bs) {

        bdrv_drained_end(bs);

    }

}



void blk_drain_all(void)

{

    bdrv_drain_all();

    BlockBackend *blk = NULL;



    bdrv_drain_all_begin();



    while ((blk = blk_all_next(blk)) != NULL) {

        AioContext *ctx = blk_get_aio_context(blk);



        aio_context_acquire(ctx);



        /* We may have -ENOMEDIUM completions in flight */

        AIO_WAIT_WHILE(&blk->wait, ctx,

                atomic_mb_read(&blk->in_flight) > 0);



        aio_context_release(ctx);

    }



    bdrv_drain_all_end();

}



void blk_set_on_error(BlockBackend *blk, BlockdevOnError on_read_error,