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block/export: don't require AioContext lock around blk_exp_ref/unref()

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The FUSE export calls blk_exp_ref/unref() without the AioContext lock.
Instead of fixing the FUSE export, adjust blk_exp_ref/unref() so they
work without the AioContext lock. This way it's less error-prone.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230516190238.8401-15-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-05-16 15:02:32 -04:00 committed by Kevin Wolf
parent 195332c1d9
commit 3d499a43a2
3 changed files with 8 additions and 11 deletions
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13
block/export/export.c
View file

@ -204,11 +204,10 @@ fail:
return NULL; return NULL;
} }
/* Callers must hold exp->ctx lock */
void blk_exp_ref(BlockExport *exp) void blk_exp_ref(BlockExport *exp)
{ {
assert(exp->refcount > 0); assert(qatomic_read(&exp->refcount) > 0);
exp->refcount++; qatomic_inc(&exp->refcount);
} }
/* Runs in the main thread */ /* Runs in the main thread */
@ -231,11 +230,10 @@ static void blk_exp_delete_bh(void *opaque)
aio_context_release(aio_context); aio_context_release(aio_context);
} }
/* Callers must hold exp->ctx lock */
void blk_exp_unref(BlockExport *exp) void blk_exp_unref(BlockExport *exp)
{ {
assert(exp->refcount > 0); assert(qatomic_read(&exp->refcount) > 0);
if (--exp->refcount == 0) { if (qatomic_fetch_dec(&exp->refcount) == 1) {
/* Touch the block_exports list only in the main thread */ /* Touch the block_exports list only in the main thread */
aio_bh_schedule_oneshot(qemu_get_aio_context(), blk_exp_delete_bh, aio_bh_schedule_oneshot(qemu_get_aio_context(), blk_exp_delete_bh,
exp); exp);
@ -343,7 +341,8 @@ void qmp_block_export_del(const char *id,
if (!has_mode) { if (!has_mode) {
mode = BLOCK_EXPORT_REMOVE_MODE_SAFE; mode = BLOCK_EXPORT_REMOVE_MODE_SAFE;
} }
if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE && exp->refcount > 1) { if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE &&
qatomic_read(&exp->refcount) > 1) {
error_setg(errp, "export '%s' still in use", exp->id); error_setg(errp, "export '%s' still in use", exp->id);
error_append_hint(errp, "Use mode='hard' to force client " error_append_hint(errp, "Use mode='hard' to force client "
"disconnect\n"); "disconnect\n");

4
block/export/vduse-blk.c
View file

@ -44,9 +44,7 @@ static void vduse_blk_inflight_inc(VduseBlkExport *vblk_exp)
{ {
if (qatomic_fetch_inc(&vblk_exp->inflight) == 0) { if (qatomic_fetch_inc(&vblk_exp->inflight) == 0) {
/* Prevent export from being deleted */ /* Prevent export from being deleted */
aio_context_acquire(vblk_exp->export.ctx);
blk_exp_ref(&vblk_exp->export); blk_exp_ref(&vblk_exp->export);
aio_context_release(vblk_exp->export.ctx);
} }
} }
@ -57,9 +55,7 @@ static void vduse_blk_inflight_dec(VduseBlkExport *vblk_exp)
aio_wait_kick(); aio_wait_kick();
/* Now the export can be deleted */ /* Now the export can be deleted */
aio_context_acquire(vblk_exp->export.ctx);
blk_exp_unref(&vblk_exp->export); blk_exp_unref(&vblk_exp->export);
aio_context_release(vblk_exp->export.ctx);
} }
} }

2
include/block/export.h
View file

@ -57,6 +57,8 @@ struct BlockExport {
* Reference count for this block export. This includes strong references * Reference count for this block export. This includes strong references
* both from the owner (qemu-nbd or the monitor) and clients connected to * both from the owner (qemu-nbd or the monitor) and clients connected to
* the export. * the export.
*
* Use atomics to access this field.
*/ */
int refcount; int refcount;