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bdev/rpc: Fix race condition for per channel bdev_get_iostat

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With per channel stats called on thread A,
spdk_bdev_for_each_channel calls
spdk_for_each_channel which immediately sends
a message to thread B.
If thread B has no workload, it may execute the
message relatively fast trying to write stats to
json_write_ctx.
As result, we may have 2 scenarious:
1. json_write_ctx is still not initialized on
thread A, so thread B dereferences a NULL pointer.
1. json_write_ctx is initialized but thread A writes
response header while thread B writes stats - it leads
to corrupted json response.

To fix this race condition, initialize json_write_ctx
before iterating bdevs/channels

Signed-off-by: Shuhei Matsumoto <smatsumoto@nvidia.com>
Signed-off-by: Alexey Marchuk <alexeymar@nvidia.com>
Reported-by: Or Gerlitz <ogerlitz@nvidia.com>
Change-Id: I5dae37f1f527437528fc8a8e9c6066f69687dec9
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/16366
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
This commit is contained in:
Shuhei Matsumoto 2023-01-20 11:17:16 +09:00 committed by Tomasz Zawadzki
parent db3869d1b2
commit 139940d6c1
1 changed files with 22 additions and 25 deletions
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47
lib/bdev/bdev_rpc.c
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@ -175,7 +175,7 @@ struct bdev_get_iostat_ctx {
};
static void
_rpc_get_iostat_started(struct rpc_get_iostat_ctx *rpc_ctx)
rpc_get_iostat_started(struct rpc_get_iostat_ctx *rpc_ctx)
{
rpc_ctx->w = spdk_jsonrpc_begin_result(rpc_ctx->request);
@ -184,23 +184,6 @@ _rpc_get_iostat_started(struct rpc_get_iostat_ctx *rpc_ctx)
spdk_json_write_named_uint64(rpc_ctx->w, "ticks", spdk_get_ticks());
}
static void
rpc_get_iostat_started(struct rpc_get_iostat_ctx *rpc_ctx, struct spdk_bdev_desc *desc)
{
struct spdk_bdev *bdev;
_rpc_get_iostat_started(rpc_ctx);
if (rpc_ctx->per_channel == false) {
spdk_json_write_named_array_begin(rpc_ctx->w, "bdevs");
} else {
bdev = spdk_bdev_desc_get_bdev(desc);
spdk_json_write_named_string(rpc_ctx->w, "name", spdk_bdev_get_name(bdev));
spdk_json_write_named_array_begin(rpc_ctx->w, "channels");
}
}
static void
rpc_get_iostat_done(struct rpc_get_iostat_ctx *rpc_ctx)
{
@ -380,6 +363,7 @@ rpc_bdev_get_iostat(struct spdk_jsonrpc_request *request,
struct spdk_bdev_desc *desc = NULL;
struct rpc_get_iostat_ctx *rpc_ctx;
struct bdev_get_iostat_ctx *bdev_ctx;
struct spdk_bdev *bdev;
int rc;
if (params != NULL) {
@ -429,6 +413,8 @@ rpc_bdev_get_iostat(struct spdk_jsonrpc_request *request,
rpc_ctx->per_channel = req.per_channel;
if (desc != NULL) {
bdev = spdk_bdev_desc_get_bdev(desc);
bdev_ctx = bdev_iostat_ctx_alloc(req.per_channel == false);
if (bdev_ctx == NULL) {
SPDK_ERRLOG("Failed to allocate bdev_iostat_ctx struct\n");
@ -441,13 +427,24 @@ rpc_bdev_get_iostat(struct spdk_jsonrpc_request *request,
rpc_ctx->bdev_count++;
bdev_ctx->rpc_ctx = rpc_ctx;
if (req.per_channel == false) {
spdk_bdev_get_device_stat(spdk_bdev_desc_get_bdev(desc), bdev_ctx->stat,
bdev_get_iostat_done, bdev_ctx);
spdk_bdev_get_device_stat(bdev, bdev_ctx->stat, bdev_get_iostat_done,
bdev_ctx);
} else {
spdk_bdev_for_each_channel(spdk_bdev_desc_get_bdev(desc),
/* If per_channel is true, there is no failure after here and
* we have to start RPC response before executing
* spdk_bdev_for_each_channel().
*/
rpc_get_iostat_started(rpc_ctx);
spdk_json_write_named_string(rpc_ctx->w, "name", spdk_bdev_get_name(bdev));
spdk_json_write_named_array_begin(rpc_ctx->w, "channels");
spdk_bdev_for_each_channel(bdev,
bdev_get_per_channel_stat,
bdev_ctx,
bdev_get_per_channel_stat_done);
rpc_get_iostat_done(rpc_ctx);
return;
}
}
} else {
@ -458,12 +455,12 @@ rpc_bdev_get_iostat(struct spdk_jsonrpc_request *request,
}
if (rpc_ctx->rc == 0) {
/* We want to fail the RPC for all failures. The callback function to
* spdk_bdev_for_each_channel() is executed after stack unwinding if
* successful. Hence defer starting RPC response until it is ensured that
/* We want to fail the RPC for all failures. If per_channel is false,
* it is enough to defer starting RPC response until it is ensured that
* all spdk_bdev_for_each_channel() calls will succeed or there is no bdev.
*/
rpc_get_iostat_started(rpc_ctx, desc);
rpc_get_iostat_started(rpc_ctx);
spdk_json_write_named_array_begin(rpc_ctx->w, "bdevs");
}
rpc_get_iostat_done(rpc_ctx);