nvme-pci: make nvme_pci_npages_prp() __always_inline

The only reason nvme_pci_npages_prp() could be used as a compile-time
known result in BUILD_BUG_ON() is because the compiler was always choosing
to inline the function. Under special circumstances (sanitizer coverage
functions disabled for __init functions on ARCH=um), the compiler decided
to stop inlining it:

   drivers/nvme/host/pci.c: In function 'nvme_init':
   include/linux/compiler_types.h:557:45: error: call to '__compiletime_assert_678' declared with attribute error: BUILD_BUG_ON failed: nvme_pci_npages_prp() > NVME_MAX_NR_ALLOCATIONS
     557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
         |                                             ^
   include/linux/compiler_types.h:538:25: note: in definition of macro '__compiletime_assert'
     538 |                         prefix ## suffix();                             \
         |                         ^~~~~~
   include/linux/compiler_types.h:557:9: note: in expansion of macro '_compiletime_assert'
     557 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
         |         ^~~~~~~~~~~~~~~~~~~
   include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
      39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
         |                                     ^~~~~~~~~~~~~~~~~~
   include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG'
      50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
         |         ^~~~~~~~~~~~~~~~
   drivers/nvme/host/pci.c:3804:9: note: in expansion of macro 'BUILD_BUG_ON'
    3804 |         BUILD_BUG_ON(nvme_pci_npages_prp() > NVME_MAX_NR_ALLOCATIONS);
         |         ^~~~~~~~~~~~

Force it to be __always_inline to make sure it is always available for
use with BUILD_BUG_ON().

Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Fixes: c372cdd ("nvme-pci: iod npages fits in s8")
Signed-off-by: Kees Cook <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

Author: kees

drivers/nvme/host/pci.c

@@ -390,7 +390,7 @@ static bool nvme_dbbuf_update_and_check_event(u16 value, __le32 *dbbuf_db,
  * as it only leads to a small amount of wasted memory for the lifetime of
  * the I/O.
  */
-static int nvme_pci_npages_prp(void)
+static __always_inline int nvme_pci_npages_prp(void)
 {
 	unsigned max_bytes = (NVME_MAX_KB_SZ * 1024) + NVME_CTRL_PAGE_SIZE;
 	unsigned nprps = DIV_ROUND_UP(max_bytes, NVME_CTRL_PAGE_SIZE);