x86/kgdb: use IS_ERR_PCPU() macro

x86/kgdb: use IS_ERR_PCPU() macro

Patch series "Enable strict percpu address space checks", v4.

Enable strict percpu address space checks via x86 named address space
qualifiers.  Percpu variables are declared in __seg_gs/__seg_fs named AS
and kept named AS qualified until they are dereferenced via percpu
accessor.  This approach enables various compiler checks for
cross-namespace variable assignments.

Please note that current version of sparse doesn't know anything about
__typeof_unqual__() operator.  Avoid the usage of __typeof_unqual__() when
sparse checking is active to prevent sparse errors with unknowing keyword.
The proposed patch by Dan Carpenter to implement __typeof_unqual__()
handling in sparse is located at:

https://lore.kernel.org/lkml/5b8d0dee-8fb6-45af-ba6c-7f74aff9a4b8@stanley.mountain/

This patch (of 6):

Use IS_ERR_PCPU() when checking the error pointer in the percpu address
space.  This macro adds intermediate cast to unsigned long when switching
named address spaces.

The patch will avoid future build errors due to pointer address space
mismatch with enabled strict percpu address space checks.

Link: https://lkml.kernel.org/r/20250127160709.80604-1-ubizjak@gmail.com
Link: https://lkml.kernel.org/r/20250127160709.80604-2-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Acked-by: Nadav Amit <nadav.amit@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>