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Message-ID: <202512112012.OUpR3T44-lkp@intel.com>
Date: Thu, 11 Dec 2025 20:49:42 +0800
From: kernel test robot <lkp@...el.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
"Steven Rostedt (Google)" <rostedt@...dmis.org>
Subject: kernel/unwind/deferred.c:257 unwind_deferred_request() warn:
unsigned 'bit' is never less than zero.
tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head: d358e5254674b70f34c847715ca509e46eb81e6f
commit: 49cf34c0815f93fb2ea3ab5cfbac1124bd9b45d0 unwind_user/x86: Enable frame pointer unwinding on x86
date: 6 weeks ago
config: x86_64-randconfig-161-20251211 (https://download.01.org/0day-ci/archive/20251211/202512112012.OUpR3T44-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
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@...el.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512112012.OUpR3T44-lkp@intel.com/
smatch warnings:
kernel/unwind/deferred.c:257 unwind_deferred_request() warn: unsigned 'bit' is never less than zero.
vim +/bit +257 kernel/unwind/deferred.c
b3b9cb11aa034cf Steven Rostedt 2025-07-29 204
2dffa355f6c279e Josh Poimboeuf 2025-07-29 205 /**
2dffa355f6c279e Josh Poimboeuf 2025-07-29 206 * unwind_deferred_request - Request a user stacktrace on task kernel exit
2dffa355f6c279e Josh Poimboeuf 2025-07-29 207 * @work: Unwind descriptor requesting the trace
2dffa355f6c279e Josh Poimboeuf 2025-07-29 208 * @cookie: The cookie of the first request made for this task
2dffa355f6c279e Josh Poimboeuf 2025-07-29 209 *
2dffa355f6c279e Josh Poimboeuf 2025-07-29 210 * Schedule a user space unwind to be done in task work before exiting the
2dffa355f6c279e Josh Poimboeuf 2025-07-29 211 * kernel.
2dffa355f6c279e Josh Poimboeuf 2025-07-29 212 *
2dffa355f6c279e Josh Poimboeuf 2025-07-29 213 * The returned @cookie output is the generated cookie of the very first
2dffa355f6c279e Josh Poimboeuf 2025-07-29 214 * request for a user space stacktrace for this task since it entered the
2dffa355f6c279e Josh Poimboeuf 2025-07-29 215 * kernel. It can be from a request by any caller of this infrastructure.
2dffa355f6c279e Josh Poimboeuf 2025-07-29 216 * Its value will also be passed to the callback function. It can be
2dffa355f6c279e Josh Poimboeuf 2025-07-29 217 * used to stitch kernel and user stack traces together in post-processing.
2dffa355f6c279e Josh Poimboeuf 2025-07-29 218 *
2dffa355f6c279e Josh Poimboeuf 2025-07-29 219 * It's valid to call this function multiple times for the same @work within
2dffa355f6c279e Josh Poimboeuf 2025-07-29 220 * the same task entry context. Each call will return the same cookie
2dffa355f6c279e Josh Poimboeuf 2025-07-29 221 * while the task hasn't left the kernel. If the callback is not pending
2dffa355f6c279e Josh Poimboeuf 2025-07-29 222 * because it has already been previously called for the same entry context,
2dffa355f6c279e Josh Poimboeuf 2025-07-29 223 * it will be called again with the same stack trace and cookie.
2dffa355f6c279e Josh Poimboeuf 2025-07-29 224 *
be3d526a5b34109 Steven Rostedt 2025-07-29 225 * Return: 0 if the callback successfully was queued.
be3d526a5b34109 Steven Rostedt 2025-07-29 226 * 1 if the callback is pending or was already executed.
2dffa355f6c279e Josh Poimboeuf 2025-07-29 227 * Negative if there's an error.
2dffa355f6c279e Josh Poimboeuf 2025-07-29 228 * @cookie holds the cookie of the first request by any user
2dffa355f6c279e Josh Poimboeuf 2025-07-29 229 */
2dffa355f6c279e Josh Poimboeuf 2025-07-29 230 int unwind_deferred_request(struct unwind_work *work, u64 *cookie)
2dffa355f6c279e Josh Poimboeuf 2025-07-29 231 {
2dffa355f6c279e Josh Poimboeuf 2025-07-29 232 struct unwind_task_info *info = ¤t->unwind_info;
a38a64712e740d6 Peter Zijlstra 2025-09-22 233 int twa_mode = TWA_RESUME;
be3d526a5b34109 Steven Rostedt 2025-07-29 234 unsigned long old, bits;
357eda2d745054e Steven Rostedt 2025-07-29 235 unsigned long bit;
2dffa355f6c279e Josh Poimboeuf 2025-07-29 236 int ret;
2dffa355f6c279e Josh Poimboeuf 2025-07-29 237
2dffa355f6c279e Josh Poimboeuf 2025-07-29 238 *cookie = 0;
2dffa355f6c279e Josh Poimboeuf 2025-07-29 239
2dffa355f6c279e Josh Poimboeuf 2025-07-29 240 if ((current->flags & (PF_KTHREAD | PF_EXITING)) ||
2dffa355f6c279e Josh Poimboeuf 2025-07-29 241 !user_mode(task_pt_regs(current)))
2dffa355f6c279e Josh Poimboeuf 2025-07-29 242 return -EINVAL;
2dffa355f6c279e Josh Poimboeuf 2025-07-29 243
055c7060e7ca71b Steven Rostedt 2025-07-29 244 /*
055c7060e7ca71b Steven Rostedt 2025-07-29 245 * NMI requires having safe cmpxchg operations.
055c7060e7ca71b Steven Rostedt 2025-07-29 246 * Trigger a warning to make it obvious that an architecture
055c7060e7ca71b Steven Rostedt 2025-07-29 247 * is using this in NMI when it should not be.
055c7060e7ca71b Steven Rostedt 2025-07-29 248 */
a38a64712e740d6 Peter Zijlstra 2025-09-22 249 if (in_nmi()) {
a38a64712e740d6 Peter Zijlstra 2025-09-22 250 if (WARN_ON_ONCE(!CAN_USE_IN_NMI))
055c7060e7ca71b Steven Rostedt 2025-07-29 251 return -EINVAL;
a38a64712e740d6 Peter Zijlstra 2025-09-22 252 twa_mode = TWA_NMI_CURRENT;
a38a64712e740d6 Peter Zijlstra 2025-09-22 253 }
055c7060e7ca71b Steven Rostedt 2025-07-29 254
357eda2d745054e Steven Rostedt 2025-07-29 255 /* Do not allow cancelled works to request again */
357eda2d745054e Steven Rostedt 2025-07-29 256 bit = READ_ONCE(work->bit);
357eda2d745054e Steven Rostedt 2025-07-29 @257 if (WARN_ON_ONCE(bit < 0))
357eda2d745054e Steven Rostedt 2025-07-29 258 return -EINVAL;
357eda2d745054e Steven Rostedt 2025-07-29 259
357eda2d745054e Steven Rostedt 2025-07-29 260 /* Only need the mask now */
357eda2d745054e Steven Rostedt 2025-07-29 261 bit = BIT(bit);
357eda2d745054e Steven Rostedt 2025-07-29 262
2dffa355f6c279e Josh Poimboeuf 2025-07-29 263 guard(irqsave)();
2dffa355f6c279e Josh Poimboeuf 2025-07-29 264
2dffa355f6c279e Josh Poimboeuf 2025-07-29 265 *cookie = get_cookie(info);
2dffa355f6c279e Josh Poimboeuf 2025-07-29 266
639214f65b1db87 Peter Zijlstra 2025-09-22 267 old = atomic_long_read(&info->unwind_mask);
055c7060e7ca71b Steven Rostedt 2025-07-29 268
be3d526a5b34109 Steven Rostedt 2025-07-29 269 /* Is this already queued or executed */
be3d526a5b34109 Steven Rostedt 2025-07-29 270 if (old & bit)
2dffa355f6c279e Josh Poimboeuf 2025-07-29 271 return 1;
2dffa355f6c279e Josh Poimboeuf 2025-07-29 272
be3d526a5b34109 Steven Rostedt 2025-07-29 273 /*
be3d526a5b34109 Steven Rostedt 2025-07-29 274 * This work's bit hasn't been set yet. Now set it with the PENDING
be3d526a5b34109 Steven Rostedt 2025-07-29 275 * bit and fetch the current value of unwind_mask. If ether the
be3d526a5b34109 Steven Rostedt 2025-07-29 276 * work's bit or PENDING was already set, then this is already queued
be3d526a5b34109 Steven Rostedt 2025-07-29 277 * to have a callback.
be3d526a5b34109 Steven Rostedt 2025-07-29 278 */
be3d526a5b34109 Steven Rostedt 2025-07-29 279 bits = UNWIND_PENDING | bit;
639214f65b1db87 Peter Zijlstra 2025-09-22 280 old = atomic_long_fetch_or(bits, &info->unwind_mask);
be3d526a5b34109 Steven Rostedt 2025-07-29 281 if (old & bits) {
be3d526a5b34109 Steven Rostedt 2025-07-29 282 /*
be3d526a5b34109 Steven Rostedt 2025-07-29 283 * If the work's bit was set, whatever set it had better
be3d526a5b34109 Steven Rostedt 2025-07-29 284 * have also set pending and queued a callback.
be3d526a5b34109 Steven Rostedt 2025-07-29 285 */
be3d526a5b34109 Steven Rostedt 2025-07-29 286 WARN_ON_ONCE(!(old & UNWIND_PENDING));
be3d526a5b34109 Steven Rostedt 2025-07-29 287 return old & bit;
be3d526a5b34109 Steven Rostedt 2025-07-29 288 }
be3d526a5b34109 Steven Rostedt 2025-07-29 289
2dffa355f6c279e Josh Poimboeuf 2025-07-29 290 /* The work has been claimed, now schedule it. */
a38a64712e740d6 Peter Zijlstra 2025-09-22 291 ret = task_work_add(current, &info->work, twa_mode);
2dffa355f6c279e Josh Poimboeuf 2025-07-29 292
be3d526a5b34109 Steven Rostedt 2025-07-29 293 if (WARN_ON_ONCE(ret))
639214f65b1db87 Peter Zijlstra 2025-09-22 294 atomic_long_set(&info->unwind_mask, 0);
be3d526a5b34109 Steven Rostedt 2025-07-29 295
be3d526a5b34109 Steven Rostedt 2025-07-29 296 return ret;
2dffa355f6c279e Josh Poimboeuf 2025-07-29 297 }
2dffa355f6c279e Josh Poimboeuf 2025-07-29 298
:::::: The code at line 257 was first introduced by commit
:::::: 357eda2d745054eb737397368bc9b0f84814b0a5 unwind deferred: Use SRCU unwind_deferred_task_work()
:::::: TO: Steven Rostedt <rostedt@...dmis.org>
:::::: CC: Steven Rostedt (Google) <rostedt@...dmis.org>
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