From c86422c5549c0983b4b4525b8f56a1c69dd67aa1 Mon Sep 17 00:00:00 2001 From: Emanuele Giuseppe Esposito Date: Fri, 13 Jan 2023 21:42:04 +0100 Subject: block: Convert bdrv_refresh_total_sectors() to co_wrapper_mixed BlockDriver->bdrv_getlength is categorized as IO callback, and it currently doesn't run in a coroutine. We should let it take a graph rdlock since the callback traverses the block nodes graph, which however is only possible in a coroutine. Therefore turn it into a co_wrapper to move the actual function into a coroutine where the lock can be taken. Because now this function creates a new coroutine and polls, we need to take the AioContext lock where it is missing, for the only reason that internally co_wrapper calls AIO_WAIT_WHILE and it expects to release the AioContext lock. This is especially messy when a co_wrapper creates a coroutine and polls in bdrv_open_driver, because this function has so many callers in so many context that it can easily lead to deadlocks. Therefore the new rule for bdrv_open_driver is that the caller must always hold the AioContext lock of the given bs (except if it is a coroutine), because the function calls bdrv_refresh_total_sectors() which is now a co_wrapper. Once the rwlock is ultimated and placed in every place it needs to be, we will poll using AIO_WAIT_WHILE_UNLOCKED and remove the AioContext lock. Signed-off-by: Emanuele Giuseppe Esposito Signed-off-by: Kevin Wolf Message-Id: <20230113204212.359076-7-kwolf@redhat.com> Reviewed-by: Emanuele Giuseppe Esposito Signed-off-by: Kevin Wolf --- block.c | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) (limited to 'block.c') diff --git a/block.c b/block.c index b6c6b17cb2..ee6f90990e 100644 --- a/block.c +++ b/block.c @@ -1035,7 +1035,8 @@ static int find_image_format(BlockBackend *file, const char *filename, * Set the current 'total_sectors' value * Return 0 on success, -errno on error. */ -int bdrv_refresh_total_sectors(BlockDriverState *bs, int64_t hint) +int coroutine_fn bdrv_co_refresh_total_sectors(BlockDriverState *bs, + int64_t hint) { BlockDriver *drv = bs->drv; IO_CODE(); @@ -1044,13 +1045,13 @@ int bdrv_refresh_total_sectors(BlockDriverState *bs, int64_t hint) return -ENOMEDIUM; } - /* Do not attempt drv->bdrv_getlength() on scsi-generic devices */ + /* Do not attempt drv->bdrv_co_getlength() on scsi-generic devices */ if (bdrv_is_sg(bs)) return 0; /* query actual device if possible, otherwise just trust the hint */ - if (drv->bdrv_getlength) { - int64_t length = drv->bdrv_getlength(bs); + if (drv->bdrv_co_getlength) { + int64_t length = drv->bdrv_co_getlength(bs); if (length < 0) { return length; } @@ -1601,6 +1602,11 @@ out: g_free(gen_node_name); } +/* + * The caller must always hold @bs AioContext lock, because this function calls + * bdrv_refresh_total_sectors() which polls when called from non-coroutine + * context. + */ static int bdrv_open_driver(BlockDriverState *bs, BlockDriver *drv, const char *node_name, QDict *options, int open_flags, Error **errp) @@ -3796,6 +3802,10 @@ out: * The reference parameter may be used to specify an existing block device which * should be opened. If specified, neither options nor a filename may be given, * nor can an existing BDS be reused (that is, *pbs has to be NULL). + * + * The caller must always hold @filename AioContext lock, because this + * function eventually calls bdrv_refresh_total_sectors() which polls + * when called from non-coroutine context. */ static BlockDriverState *bdrv_open_inherit(const char *filename, const char *reference, @@ -4084,6 +4094,11 @@ close_and_fail: return NULL; } +/* + * The caller must always hold @filename AioContext lock, because this + * function eventually calls bdrv_refresh_total_sectors() which polls + * when called from non-coroutine context. + */ BlockDriverState *bdrv_open(const char *filename, const char *reference, QDict *options, int flags, Error **errp) { @@ -5800,7 +5815,7 @@ BlockMeasureInfo *bdrv_measure(BlockDriver *drv, QemuOpts *opts, /** * Return number of sectors on success, -errno on error. */ -int64_t bdrv_nb_sectors(BlockDriverState *bs) +int64_t coroutine_fn bdrv_co_nb_sectors(BlockDriverState *bs) { BlockDriver *drv = bs->drv; IO_CODE(); @@ -5809,7 +5824,7 @@ int64_t bdrv_nb_sectors(BlockDriverState *bs) return -ENOMEDIUM; if (drv->has_variable_length) { - int ret = bdrv_refresh_total_sectors(bs, bs->total_sectors); + int ret = bdrv_co_refresh_total_sectors(bs, bs->total_sectors); if (ret < 0) { return ret; } @@ -5821,11 +5836,12 @@ int64_t bdrv_nb_sectors(BlockDriverState *bs) * Return length in bytes on success, -errno on error. * The length is always a multiple of BDRV_SECTOR_SIZE. */ -int64_t bdrv_getlength(BlockDriverState *bs) +int64_t coroutine_fn bdrv_co_getlength(BlockDriverState *bs) { - int64_t ret = bdrv_nb_sectors(bs); + int64_t ret; IO_CODE(); + ret = bdrv_co_nb_sectors(bs); if (ret < 0) { return ret; } -- cgit v1.2.3