crypto: iaa - Fix IAA disabling that occurs when sync_mode is set to 'async'

With the latest mm-unstable, setting the iaa_crypto sync_mode to 'async'
causes crypto testmgr.c test_acomp() failure and dmesg call traces, and
zswap being unable to use 'deflate-iaa' as a compressor:

echo async > /sys/bus/dsa/drivers/crypto/sync_mode

[ 255.271030] zswap: compressor deflate-iaa not available
[ 369.960673] INFO: task cryptomgr_test:4889 blocked for more than 122 seconds.
[ 369.970127] Not tainted 6.13.0-rc1-mm-unstable-12-16-2024+ #324
[ 369.977411] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 369.986246] task:cryptomgr_test state:D stack:0 pid:4889 tgid:4889 ppid:2 flags:0x00004000
[ 369.986253] Call Trace:
[ 369.986256] <TASK>
[ 369.986260] __schedule+0x45c/0xfa0
[ 369.986273] schedule+0x2e/0xb0
[ 369.986277] schedule_timeout+0xe7/0x100
[ 369.986284] ? __prepare_to_swait+0x4e/0x70
[ 369.986290] wait_for_completion+0x8d/0x120
[ 369.986293] test_acomp+0x284/0x670
[ 369.986305] ? __pfx_cryptomgr_test+0x10/0x10
[ 369.986312] alg_test_comp+0x263/0x440
[ 369.986315] ? sched_balance_newidle+0x259/0x430
[ 369.986320] ? __pfx_cryptomgr_test+0x10/0x10
[ 369.986323] alg_test.part.27+0x103/0x410
[ 369.986326] ? __schedule+0x464/0xfa0
[ 369.986330] ? __pfx_cryptomgr_test+0x10/0x10
[ 369.986333] cryptomgr_test+0x20/0x40
[ 369.986336] kthread+0xda/0x110
[ 369.986344] ? __pfx_kthread+0x10/0x10
[ 369.986346] ret_from_fork+0x2d/0x40
[ 369.986355] ? __pfx_kthread+0x10/0x10
[ 369.986358] ret_from_fork_asm+0x1a/0x30
[ 369.986365] </TASK>

This happens because the only async polling without interrupts that
iaa_crypto currently implements is with the 'sync' mode. With 'async',
iaa_crypto calls to compress/decompress submit the descriptor and return
-EINPROGRESS, without any mechanism in the driver to poll for
completions. Hence callers such as test_acomp() in crypto/testmgr.c or
zswap, that wrap the calls to crypto_acomp_compress() and
crypto_acomp_decompress() in synchronous wrappers, will block
indefinitely. Even before zswap can notice this problem, the crypto
testmgr.c's test_acomp() will fail and prevent registration of
"deflate-iaa" as a valid crypto acomp algorithm, thereby disallowing the
use of "deflate-iaa" as a zswap compress (zswap will fall-back to the
default compressor in this case).

To fix this issue, this patch modifies the iaa_crypto sync_mode set
function to treat 'async' equivalent to 'sync', so that the correct and
only supported driver async polling without interrupts implementation is
enabled, and zswap can use 'deflate-iaa' as the compressor.

Hence, with this patch, this is what will happen:

echo async > /sys/bus/dsa/drivers/crypto/sync_mode
cat /sys/bus/dsa/drivers/crypto/sync_mode
sync

There are no crypto/testmgr.c test_acomp() errors, no call traces and zswap
can use 'deflate-iaa' without any errors. The iaa_crypto documentation has
also been updated to mention this caveat with 'async' and what to expect
with this fix.

True iaa_crypto async polling without interrupts is enabled in patch
"crypto: iaa - Implement batch_compress(), batch_decompress() API in
iaa_crypto." [1] which is under review as part of the "zswap IAA compress
batching" patch-series [2]. Until this is merged, we would appreciate it if
this current patch can be considered for a hotfix.

[1]: https://patchwork.kernel.org/project/linux-mm/patch/[e-mail]/
[2]: https://patchwork.kernel.org/project/linux-mm/list/?series=920084

Fixes: 09646c98d ("crypto: iaa - Add irq support for the crypto async interface")
Signed-off-by: Kanchana P Sridhar <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

Documentation/driver-api/crypto/iaa/iaa-crypto.rst

···
       echo async_irq > /sys/bus/dsa/drivers/crypto/sync_mode
 
     Async mode without interrupts (caller must poll) can be enabled by
-    writing 'async' to it::
+    writing 'async' to it (please see Caveat)::
 
       echo async > /sys/bus/dsa/drivers/crypto/sync_mode
 
···
       echo sync > /sys/bus/dsa/drivers/crypto/sync_mode
 
     The default mode is 'sync'.
+
+    Caveat: since the only mechanism that iaa_crypto currently implements
+    for async polling without interrupts is via the 'sync' mode as
+    described earlier, writing 'async' to
+    '/sys/bus/dsa/drivers/crypto/sync_mode' will internally enable the
+    'sync' mode. This is to ensure correct iaa_crypto behavior until true
+    async polling without interrupts is enabled in iaa_crypto.
 
 .. _iaa_default_config:
 

drivers/crypto/intel/iaa/iaa_crypto_main.c

···
 		async_mode = false;
 		use_irq = false;
 	} else if (sysfs_streq(name, "async")) {
-		async_mode = true;
+		async_mode = false;
 		use_irq = false;
 	} else if (sysfs_streq(name, "async_irq")) {
 		async_mode = true;