Re: [EXTERNAL] fs/smb/client/sess.c:160:5: warning: stack frame size (1152) exceeds limit (1024) in 'cifs_try_adding_channels'

From: Nathan Chancellor
Date: Thu Jul 27 2023 - 12:40:22 EST

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Hi Steve,

On Thu, Jul 27, 2023 at 03:36:11AM +0000, Steven French wrote:
> Does anyone recognize the problem here - the stack size it is complaining about has a small stack usage not a large one
> cifs_try_adding_channels has five pointers and five ints on the stack. That seems small - not large. It is called by cifs_mount which doesn't seem too bad in its stack usage either.
>
> Any ideas why the stack size complaint is made?

Unfortunately, it seems like a recent-ish LLVM change removed the handy
spill/variable information that would have shed a little more immediate
light on this situation:

https://github.com/ClangBuiltLinux/linux/issues/1894

Building with a version that has that reveals:

fs/smb/client/sess.c:160:5: warning: stack frame size (1152) exceeds limit (1024) in 'cifs_try_adding_channels' [-Wframe-larger-than]
int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
^
412/1152 (35.76%) spills, 740/1152 (64.24%) variables
1 warning generated.

The spills are definitely not great but it looks like there is a
moderately large stack variable in cifs_ses_add_channel(), which gets
inlined into cifs_try_adding_channels(). Unfortunately, pahole appears
to be borked for me but -Rpass-analysis=stack-frame-layout shows it:

fs/smb/client/sess.c:161:1: remark:
Function: cifs_try_adding_channels
Offset: [SP-8], Type: Spill, Align: 8, Size: 8
Offset: [SP-16], Type: Spill, Align: 8, Size: 8
Offset: [SP-24], Type: Spill, Align: 8, Size: 8
Offset: [SP-32], Type: Spill, Align: 8, Size: 8
Offset: [SP-40], Type: Spill, Align: 8, Size: 8
Offset: [SP-48], Type: Spill, Align: 8, Size: 8
Offset: [SP-56], Type: Spill, Align: 8, Size: 8
Offset: [SP-64], Type: Spill, Align: 8, Size: 8
Offset: [SP-72], Type: Spill, Align: 8, Size: 8
Offset: [SP-80], Type: Spill, Align: 8, Size: 8
Offset: [SP-88], Type: Protector, Align: 8, Size: 8
Offset: [SP-712], Type: Variable, Align: 8, Size: 624 <-- ctx, struct smb3_fs_context
Offset: [SP-801], Type: Variable, Align: 1, Size: 89
Offset: [SP-816], Type: Spill, Align: 8, Size: 8
Offset: [SP-824], Type: Spill, Align: 8, Size: 8
Offset: [SP-832], Type: Spill, Align: 8, Size: 8
Offset: [SP-840], Type: Spill, Align: 8, Size: 8
Offset: [SP-848], Type: Spill, Align: 8, Size: 8
Offset: [SP-856], Type: Spill, Align: 8, Size: 8
Offset: [SP-864], Type: Spill, Align: 8, Size: 8
Offset: [SP-872], Type: Spill, Align: 8, Size: 8
Offset: [SP-880], Type: Spill, Align: 8, Size: 8
Offset: [SP-888], Type: Spill, Align: 8, Size: 8
Offset: [SP-896], Type: Spill, Align: 8, Size: 8
Offset: [SP-904], Type: Spill, Align: 8, Size: 8
Offset: [SP-912], Type: Spill, Align: 8, Size: 8
Offset: [SP-920], Type: Spill, Align: 8, Size: 8
Offset: [SP-928], Type: Spill, Align: 8, Size: 8
Offset: [SP-936], Type: Spill, Align: 8, Size: 8
Offset: [SP-944], Type: Spill, Align: 8, Size: 8
Offset: [SP-952], Type: Spill, Align: 8, Size: 8
Offset: [SP-960], Type: Spill, Align: 8, Size: 8
Offset: [SP-968], Type: Spill, Align: 8, Size: 8
Offset: [SP-976], Type: Spill, Align: 8, Size: 8
Offset: [SP-984], Type: Spill, Align: 8, Size: 8
Offset: [SP-992], Type: Spill, Align: 8, Size: 8
Offset: [SP-1000], Type: Spill, Align: 8, Size: 8
Offset: [SP-1008], Type: Spill, Align: 8, Size: 8
Offset: [SP-1016], Type: Spill, Align: 8, Size: 8
Offset: [SP-1024], Type: Spill, Align: 8, Size: 8
Offset: [SP-1028], Type: Spill, Align: 4, Size: 4
Offset: [SP-1040], Type: Spill, Align: 8, Size: 8
Offset: [SP-1048], Type: Spill, Align: 8, Size: 8
Offset: [SP-1056], Type: Spill, Align: 8, Size: 8
Offset: [SP-1064], Type: Spill, Align: 8, Size: 8
Offset: [SP-1072], Type: Spill, Align: 8, Size: 8
Offset: [SP-1080], Type: Spill, Align: 8, Size: 8
Offset: [SP-1088], Type: Spill, Align: 8, Size: 8
Offset: [SP-1096], Type: Spill, Align: 8, Size: 8
Offset: [SP-1104], Type: Spill, Align: 8, Size: 8
Offset: [SP-1112], Type: Spill, Align: 8, Size: 8
Offset: [SP-1120], Type: Spill, Align: 8, Size: 8
Offset: [SP-1124], Type: Spill, Align: 4, Size: 4
Offset: [SP-1128], Type: Spill, Align: 4, Size: 4
Offset: [SP-1136], Type: Spill, Align: 8, Size: 8
Offset: [SP-1144], Type: Spill, Align: 8, Size: 8
Offset: [SP-1152], Type: Spill, Align: 8, Size: 8 [-Rpass-analysis=stack-frame-layout]
161 | {
| ^

There is probably more we can do on the compiler side to improve the
spills but I suspect marking cifs_ses_add_channel() as
noinline_for_stack or switching ctx to a head allocation would resolve
this.

Cheers,
Nathan

> -----Original Message-----
> From: kernel test robot <lkp@xxxxxxxxx>
> Sent: Wednesday, July 26, 2023 5:44 PM
> To: Steven French <Steven.French@xxxxxxxxxxxxx>
> Cc: llvm@xxxxxxxxxxxxxxx; oe-kbuild-all@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [EXTERNAL] fs/smb/client/sess.c:160:5: warning: stack frame size (1152) exceeds limit (1024) in 'cifs_try_adding_channels'
>
> Hi Steve,
>
> First bad commit (maybe != root cause):
>
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head: 0a8db05b571ad5b8d5c8774a004c0424260a90bd
> commit: 38c8a9a52082579090e34c033d439ed2cd1a462d smb: move client and server files to common directory fs/smb
> date: 9 weeks ago
> config: mips-loongson2k_defconfig (https://download.01.org/0day-ci/archive/20230727/202307270640.5ODmPwDl-lkp@xxxxxxxxx/config)
> compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
> reproduce: (https://download.01.org/0day-ci/archive/20230727/202307270640.5ODmPwDl-lkp@xxxxxxxxx/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> | Closes:
> | https://lore/
> | .kernel.org%2Foe-kbuild-all%2F202307270640.5ODmPwDl-lkp%40intel.com%2F
> | &data=05%7C01%7CSteven.French%40microsoft.com%7C2cc584fd937a4cd5b9d008
> | db8e29f75b%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C63826008313023
> | 4737%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBT
> | iI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=AauGIxZRPM5DK1J5j6lyEp
> | jOkArxfVtIUAnmPcxcCQs%3D&reserved=0
>
> All warnings (new ones prefixed by >>):
>
> >> fs/smb/client/sess.c:160:5: warning: stack frame size (1152) exceeds
> >> limit (1024) in 'cifs_try_adding_channels' [-Wframe-larger-than]
> 160 | int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
> | ^
> 1 warning generated.
>
>
> vim +/cifs_try_adding_channels +160 fs/smb/client/sess.c
>
> b54034a73baf9f fs/cifs/sess.c Shyam Prasad N 2022-01-03 158
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 159 /* returns number of channels added */ 387ec58f339b0c fs/cifs/sess.c Ronnie Sahlberg 2020-12-14 @160 int cifs_try_adding_channels(struct cifs_sb_info *cifs_sb, struct cifs_ses *ses)
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 161 {
> 90c49fce1c43e1 fs/cifs/sess.c Paulo Alcantara 2023-04-21 162 struct TCP_Server_Info *server = ses->server;
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 163 int old_chan_count, new_chan_count;
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 164 int left;
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 165 int rc = 0;
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 166 int tries = 0;
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 167 struct cifs_server_iface *iface = NULL, *niface = NULL;
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 168
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 169 spin_lock(&ses->chan_lock);
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 170
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 171 new_chan_count = old_chan_count = ses->chan_count;
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 172 left = ses->chan_max - ses->chan_count;
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 173
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 174 if (left <= 0) {
> 88b024f556fcd5 fs/cifs/sess.c Shyam Prasad N 2021-11-19 175 spin_unlock(&ses->chan_lock);
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 176 cifs_dbg(FYI,
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 177 "ses already at max_channels (%zu), nothing to open\n",
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 178 ses->chan_max);
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 179 return 0;
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 180 }
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 181
> 90c49fce1c43e1 fs/cifs/sess.c Paulo Alcantara 2023-04-21 182 if (server->dialect < SMB30_PROT_ID) {
> 53923e0fe2098f fs/cifs/sess.c Steve French 2022-02-16 183 spin_unlock(&ses->chan_lock);
> 53923e0fe2098f fs/cifs/sess.c Steve French 2022-02-16 184 cifs_dbg(VFS, "multichannel is not supported on this protocol version, use 3.0 or above\n");
> 53923e0fe2098f fs/cifs/sess.c Steve French 2022-02-16 185 return 0;
> 53923e0fe2098f fs/cifs/sess.c Steve French 2022-02-16 186 }
> 53923e0fe2098f fs/cifs/sess.c Steve French 2022-02-16 187
> 90c49fce1c43e1 fs/cifs/sess.c Paulo Alcantara 2023-04-21 188 if (!(server->capabilities & SMB2_GLOBAL_CAP_MULTI_CHANNEL)) {
> 9c2dc11df50d1c fs/cifs/sess.c Steve French 2021-05-07 189 ses->chan_max = 1;
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 190 spin_unlock(&ses->chan_lock);
> 90c49fce1c43e1 fs/cifs/sess.c Paulo Alcantara 2023-04-21 191 cifs_server_dbg(VFS, "no multichannel support\n");
> 9c2dc11df50d1c fs/cifs/sess.c Steve French 2021-05-07 192 return 0;
> 9c2dc11df50d1c fs/cifs/sess.c Steve French 2021-05-07 193 }
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 194 spin_unlock(&ses->chan_lock);
> 9c2dc11df50d1c fs/cifs/sess.c Steve French 2021-05-07 195
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 196 /*
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 197 * Keep connecting to same, fastest, iface for all channels as
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 198 * long as its RSS. Try next fastest one if not RSS or channel
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 199 * creation fails.
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 200 */
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 201 spin_lock(&ses->iface_lock);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 202 iface = list_first_entry(&ses->iface_list, struct cifs_server_iface,
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 203 iface_head);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 204 spin_unlock(&ses->iface_lock);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 205
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 206 while (left > 0) {
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 207
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 208 tries++;
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 209 if (tries > 3*ses->chan_max) {
> bbbf9eafbfdaa2 fs/cifs/sess.c Steve French 2020-05-30 210 cifs_dbg(FYI, "too many channel open attempts (%d channels left to open)\n",
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 211 left);
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 212 break;
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 213 }
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 214
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 215 spin_lock(&ses->iface_lock);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 216 if (!ses->iface_count) {
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 217 spin_unlock(&ses->iface_lock);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 218 break;
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 219 }
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 220
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 221 list_for_each_entry_safe_from(iface, niface, &ses->iface_list,
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 222 iface_head) {
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 223 /* skip ifaces that are unusable */
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 224 if (!iface->is_active ||
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 225 (is_ses_using_iface(ses, iface) &&
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 226 !iface->rss_capable)) {
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 227 continue;
> 65a37a34145ca6 fs/cifs/sess.c Aurelien Aptel 2019-11-20 228 }
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 229
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 230 /* take ref before unlock */
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 231 kref_get(&iface->refcount);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 232
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 233 spin_unlock(&ses->iface_lock);
> 387ec58f339b0c fs/cifs/sess.c Ronnie Sahlberg 2020-12-14 234 rc = cifs_ses_add_channel(cifs_sb, ses, iface);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 235 spin_lock(&ses->iface_lock);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 236
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 237 if (rc) {
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 238 cifs_dbg(VFS, "failed to open extra channel on iface:%pIS rc=%d\n",
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 239 &iface->sockaddr,
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 240 rc);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 241 kref_put(&iface->refcount, release_iface);
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 242 continue;
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 243 }
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 244
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 245 cifs_dbg(FYI, "successfully opened new channel on iface:%pIS\n",
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 246 &iface->sockaddr);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 247 break;
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 248 }
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 249 spin_unlock(&ses->iface_lock);
> aa45dadd34e44f fs/cifs/sess.c Shyam Prasad N 2022-01-01 250
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 251 left--;
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 252 new_chan_count++;
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 253 }
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 254
> 724244cdb38285 fs/cifs/sess.c Shyam Prasad N 2021-07-19 255 return new_chan_count - old_chan_count;
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 256 }
> d70e9fa5588476 fs/cifs/sess.c Aurelien Aptel 2019-09-20 257
>
> :::::: The code at line 160 was first introduced by commit
> :::::: 387ec58f339b0c45e3767395f11fa8dd3772131e cifs: simplify handling of cifs_sb/ctx->local_nls
>
> :::::: TO: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
> :::::: CC: Steve French <stfrench@xxxxxxxxxxxxx>
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
>

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