Re: [PATCH v2 tip/perf/core 5/5] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution

Re: [PATCH v2 tip/perf/core 5/5] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution

[kernel test robot]

Hi Andrii,

kernel test robot noticed the following build errors:

[auto build test ERROR on tip/perf/core]

url:    https://github.com/intel-lab-lkp/linux/commits/Andrii-Nakryiko/mm-introduce-mmap_lock_speculation_-start-end/20241002-065354
base:   tip/perf/core
patch link:    https://lore.kernel.org/r/20241001225207.2215639-6-andrii%40kernel.org
patch subject: [PATCH v2 tip/perf/core 5/5] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution
config: i386-defconfig (https://download.01.org/0day-ci/archive/20241005/202410050846.Zbsm9OI1-lkp@intel.com/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241005/202410050846.Zbsm9OI1-lkp@intel.com/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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202410050846.Zbsm9OI1-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/events/uprobes.c:2098:39: error: incompatible pointer types passing 'long *' to parameter of type 'int *' [-Werror,-Wincompatible-pointer-types]
    2098 |         if (!mmap_lock_speculation_start(mm, &seq))
         |                                              ^~~~
   include/linux/mmap_lock.h:126:75: note: passing argument to parameter 'seq' here
     126 | static inline bool mmap_lock_speculation_start(struct mm_struct *mm, int *seq) { return false; }
         |                                                                           ^
   1 error generated.


vim +2098 kernel/events/uprobes.c

  2086	
  2087	static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr)
  2088	{
  2089		struct mm_struct *mm = current->mm;
  2090		struct uprobe *uprobe = NULL;
  2091		struct vm_area_struct *vma;
  2092		struct file *vm_file;
  2093		loff_t offset;
  2094		long seq;
  2095	
  2096		guard(rcu)();
  2097	
> 2098		if (!mmap_lock_speculation_start(mm, &seq))
  2099			return NULL;
  2100	
  2101		vma = vma_lookup(mm, bp_vaddr);
  2102		if (!vma)
  2103			return NULL;
  2104	
  2105		/* vm_file memory can be reused for another instance of struct file,
  2106		 * but can't be freed from under us, so it's safe to read fields from
  2107		 * it, even if the values are some garbage values; ultimately
  2108		 * find_uprobe_rcu() + mmap_lock_speculation_end() check will ensure
  2109		 * that whatever we speculatively found is correct
  2110		 */
  2111		vm_file = READ_ONCE(vma->vm_file);
  2112		if (!vm_file)
  2113			return NULL;
  2114	
  2115		offset = (loff_t)(vma->vm_pgoff << PAGE_SHIFT) + (bp_vaddr - vma->vm_start);
  2116		uprobe = find_uprobe_rcu(vm_file->f_inode, offset);
  2117		if (!uprobe)
  2118			return NULL;
  2119	
  2120		/* now double check that nothing about MM changed */
  2121		if (!mmap_lock_speculation_end(mm, seq))
  2122			return NULL;
  2123	
  2124		return uprobe;
  2125	}
  2126	

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