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block: Convert bdrv_refresh_total_sectors() to co_wrapper_mixed

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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 <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230113204212.359076-7-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Emanuele Giuseppe Esposito 2023-01-13 21:42:04 +01:00 • committed by Kevin Wolf
parent c057960c4e
commit c86422c554
35 changed files with 161 additions and 121 deletions
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6
block/filter-compress.c
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@ -55,9 +55,9 @@ static int compress_open(BlockDriverState *bs, QDict *options, int flags,
}
static int64_t compress_getlength(BlockDriverState *bs)
static int64_t coroutine_fn compress_co_getlength(BlockDriverState *bs)
{
return bdrv_getlength(bs->file->bs);
return bdrv_co_getlength(bs->file->bs);
}
@ -135,7 +135,7 @@ static BlockDriver bdrv_compress = {
.bdrv_open = compress_open,
.bdrv_child_perm = bdrv_default_perms,
.bdrv_getlength = compress_getlength,
.bdrv_co_getlength = compress_co_getlength,
.bdrv_co_preadv_part = compress_co_preadv_part,
.bdrv_co_pwritev_part = compress_co_pwritev_part,