NT_STATUS_INSUFFICIENT_RESOURCES and retrying writes to Windows 10 servers

[Steve French <smfrench@gmail.com>]

By default large file copy to Windows 10 can return MANY potentially
retryable errors on write (which we don't retry from the Linux cifs
client) which can cause cp to fail.

It did look like my patch for the problem worked (see below).  Windows
10 returns *A LOT* (about 1/3 of writes in some cases I tried) of
NT_STATUS_INSUFFICIENT_RESOURCES errors (presumably due to the
'blocking operation credit' max of 64 in Windows 10 - see note 203 of
MS-SMB2).

"<203> Section 3.3.4.2: Windows-based servers enforce a configurable
blocking operation credit,
which defaults to 64 on Windows Vista SP1, Windows 7, Windows 8,
Windows 8.1, and, Windows 10,
and defaults to 512 on Windows Server 2008, Windows Server 2008 R2,
Windows Server 2012 ..."

This patch did seem to work around the problem, but perhaps we should
use far fewer credits when mounting to Windows 10 even though they are
giving us enough credits for more? Or change how we do writes to not
do synchronous writes? I haven't seen this problem to Windows 2016 or
2019 but perhaps the explanation on note 203  is all we need to know
... ie that clients can enforce a lower limit than 512

~/cifs-2.6/fs/cifs$ git diff -a
diff --git a/fs/cifs/smb2maperror.c b/fs/cifs/smb2maperror.c
index e32c264e3adb..82ade16c9501 100644
--- a/fs/cifs/smb2maperror.c
+++ b/fs/cifs/smb2maperror.c
@@ -457,7 +457,7 @@ static const struct status_to_posix_error
smb2_error_map_table[] = {
        {STATUS_FILE_INVALID, -EIO, "STATUS_FILE_INVALID"},
        {STATUS_ALLOTTED_SPACE_EXCEEDED, -EIO,
        "STATUS_ALLOTTED_SPACE_EXCEEDED"},
-       {STATUS_INSUFFICIENT_RESOURCES, -EREMOTEIO,
+       {STATUS_INSUFFICIENT_RESOURCES, -EAGAIN,
                                "STATUS_INSUFFICIENT_RESOURCES"},
        {STATUS_DFS_EXIT_PATH_FOUND, -EIO, "STATUS_DFS_EXIT_PATH_FOUND"},
        {STATUS_DEVICE_DATA_ERROR, -EIO, "STATUS_DEVICE_DATA_ERROR"},


e.g. see the number of write errors in my 8GB copy in my test below

# cat /proc/fs/cifs/Stats
Resources in use
CIFS Session: 1
Share (unique mount targets): 2
SMB Request/Response Buffer: 1 Pool size: 5
SMB Small Req/Resp Buffer: 1 Pool size: 30
Operations (MIDs): 0

0 session 0 share reconnects
Total vfs operations: 363 maximum at one time: 2

1) \\10.0.3.4\public-share
SMBs: 14879
Bytes read: 0  Bytes written: 8589934592
Open files: 2 total (local), 0 open on server
TreeConnects: 3 total 0 failed
TreeDisconnects: 0 total 0 failed
Creates: 12 total 0 failed
Closes: 10 total 0 failed
Flushes: 0 total 0 failed
Reads: 0 total 0 failed
Writes: 14838 total 5624 failed
...

Any thoughts?

Any risk that we could run into places where EAGAIN would not be
handled (there are SMB3 commands other than read and write where
NT_STATUS_INSUFFICIENT_RESOURCES could be returned in theory)

-- 
Thanks,

Steve