linux-stable.git/arch/alpha/kernel, branch v5.4.239 Linux kernel stable tree alpha: fix R_ALPHA_LITERAL reloc for large modules 2023-03-17T07:32:52+00:00 Edward Humes aurxenon@lunos.org 2022-08-27T06:49:39+00:00 737985dbcb67513789daca6628a37eceeb4cba85 [ Upstream commit b6b17a8b3ecd878d98d5472a9023ede9e669ca72 ] Previously, R_ALPHA_LITERAL relocations would overflow for large kernel modules. This was because the Alpha's apply_relocate_add was relying on the kernel's module loader to have sorted the GOT towards the very end of the module as it was mapped into memory in order to correctly assign the global pointer. While this behavior would mostly work fine for small kernel modules, this approach would overflow on kernel modules with large GOT's since the global pointer would be very far away from the GOT, and thus, certain entries would be out of range. This patch fixes this by instead using the Tru64 behavior of assigning the global pointer to be 32KB away from the start of the GOT. The change made in this patch won't work for multi-GOT kernel modules as it makes the assumption the module only has one GOT located at the beginning of .got, although for the vast majority kernel modules, this should be fine. Of the kernel modules that would previously result in a relocation error, none of them, even modules like nouveau, have even come close to filling up a single GOT, and they've all worked fine under this patch. Signed-off-by: Edward Humes <aurxenon@lunos.org> Signed-off-by: Matt Turner <mattst88@gmail.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit b6b17a8b3ecd878d98d5472a9023ede9e669ca72 ]

Previously, R_ALPHA_LITERAL relocations would overflow for large kernel
modules.

This was because the Alpha's apply_relocate_add was relying on the kernel's
module loader to have sorted the GOT towards the very end of the module as it
was mapped into memory in order to correctly assign the global pointer. While
this behavior would mostly work fine for small kernel modules, this approach
would overflow on kernel modules with large GOT's since the global pointer
would be very far away from the GOT, and thus, certain entries would be out of
range.

This patch fixes this by instead using the Tru64 behavior of assigning the
global pointer to be 32KB away from the start of the GOT. The change made
in this patch won't work for multi-GOT kernel modules as it makes the
assumption the module only has one GOT located at the beginning of .got,
although for the vast majority kernel modules, this should be fine. Of the
kernel modules that would previously result in a relocation error, none of
them, even modules like nouveau, have even come close to filling up a single
GOT, and they've all worked fine under this patch.

Signed-off-by: Edward Humes <aurxenon@lunos.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
alpha: fix FEN fault handling 2023-03-11T15:44:04+00:00 Al Viro viro@zeniv.linux.org.uk 2023-01-07T00:25:59+00:00 229edf8d7b76f927a464e620a59f7f955a003904 commit 977a3009547dad4a5bc95d91be4a58c9f7eedac0 upstream. Type 3 instruction fault (FPU insn with FPU disabled) is handled by quietly enabling FPU and returning. Which is fine, except that we need to do that both for fault in userland and in the kernel; the latter *can* legitimately happen - all it takes is this: .global _start _start: call_pal 0xae lda $0, 0 ldq $0, 0($0) - call_pal CLRFEN to clear "FPU enabled" flag and arrange for a signal delivery (SIGSEGV in this case). Fixed by moving the handling of type 3 into the common part of do_entIF(), before we check for kernel vs. user mode. Incidentally, the check for kernel mode is unidiomatic; the normal way to do that is !user_mode(regs). The difference is that the open-coded variant treats any of bits 63..3 of regs->ps being set as "it's user mode" while the normal approach is to check just the bit 3. PS is a 4-bit register and regs->ps always will have bits 63..4 clear, so the open-coded variant here is actually equivalent to !user_mode(regs). Harder to follow, though... Cc: stable@vger.kernel.org Reviewed-by: Richard Henderson <rth@twiddle.net> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 977a3009547dad4a5bc95d91be4a58c9f7eedac0 upstream.

Type 3 instruction fault (FPU insn with FPU disabled) is handled
by quietly enabling FPU and returning.  Which is fine, except that
we need to do that both for fault in userland and in the kernel;
the latter *can* legitimately happen - all it takes is this:

.global _start
_start:
        call_pal 0xae
	lda $0, 0
	ldq $0, 0($0)

- call_pal CLRFEN to clear "FPU enabled" flag and arrange for
a signal delivery (SIGSEGV in this case).

Fixed by moving the handling of type 3 into the common part of
do_entIF(), before we check for kernel vs. user mode.

Incidentally, the check for kernel mode is unidiomatic; the normal
way to do that is !user_mode(regs).  The difference is that
the open-coded variant treats any of bits 63..3 of regs->ps being
set as "it's user mode" while the normal approach is to check just
the bit 3.  PS is a 4-bit register and regs->ps always will have
bits 63..4 clear, so the open-coded variant here is actually equivalent
to !user_mode(regs).  Harder to follow, though...

Cc: stable@vger.kernel.org
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
exit: Add and use make_task_dead. 2023-02-06T06:52:49+00:00 Eric W. Biederman ebiederm@xmission.com 2023-02-02T04:42:42+00:00 9a18c9c8336fff473a2b72707bd14a52298417b8 commit 0e25498f8cd43c1b5aa327f373dd094e9a006da7 upstream. There are two big uses of do_exit. The first is it's design use to be the guts of the exit(2) system call. The second use is to terminate a task after something catastrophic has happened like a NULL pointer in kernel code. Add a function make_task_dead that is initialy exactly the same as do_exit to cover the cases where do_exit is called to handle catastrophic failure. In time this can probably be reduced to just a light wrapper around do_task_dead. For now keep it exactly the same so that there will be no behavioral differences introducing this new concept. Replace all of the uses of do_exit that use it for catastraphic task cleanup with make_task_dead to make it clear what the code is doing. As part of this rename rewind_stack_do_exit rewind_stack_and_make_dead. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
commit 0e25498f8cd43c1b5aa327f373dd094e9a006da7 upstream.

There are two big uses of do_exit.  The first is it's design use to be
the guts of the exit(2) system call.  The second use is to terminate
a task after something catastrophic has happened like a NULL pointer
in kernel code.

Add a function make_task_dead that is initialy exactly the same as
do_exit to cover the cases where do_exit is called to handle
catastrophic failure.  In time this can probably be reduced to just a
light wrapper around do_task_dead. For now keep it exactly the same so
that there will be no behavioral differences introducing this new
concept.

Replace all of the uses of do_exit that use it for catastraphic
task cleanup with make_task_dead to make it clear what the code
is doing.

As part of this rename rewind_stack_do_exit
rewind_stack_and_make_dead.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
alpha: fix syscall entry in !AUDUT_SYSCALL case 2023-01-18T10:40:53+00:00 Al Viro viro@zeniv.linux.org.uk 2021-09-18T22:18:48+00:00 f0ff6c60bc82c87e130f7fba8e322a96c12f5d1e [ Upstream commit f7b2431a6d22f7a91c567708e071dfcd6d66db14 ] We only want to take the slow path if SYSCALL_TRACE or SYSCALL_AUDIT is set; on !AUDIT_SYSCALL configs the current tree hits it whenever _any_ thread flag (including NEED_RESCHED, NOTIFY_SIGNAL, etc.) happens to be set. Fixes: a9302e843944 "alpha: Enable system-call auditing support" Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit f7b2431a6d22f7a91c567708e071dfcd6d66db14 ]

We only want to take the slow path if SYSCALL_TRACE or SYSCALL_AUDIT is
set; on !AUDIT_SYSCALL configs the current tree hits it whenever _any_
thread flag (including NEED_RESCHED, NOTIFY_SIGNAL, etc.) happens to
be set.

Fixes: a9302e843944 "alpha: Enable system-call auditing support"
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tty: the rest, stop using tty_schedule_flip() 2022-07-29T15:14:19+00:00 Jiri Slaby jslaby@suse.cz 2021-11-22T11:16:47+00:00 f20912215c9ca3403b2dbbbeac26e98663defb67 commit b68b914494df4f79b4e9b58953110574af1cb7a2 upstream. Since commit a9c3f68f3cd8d (tty: Fix low_latency BUG) in 2014, tty_flip_buffer_push() is only a wrapper to tty_schedule_flip(). We are going to remove the latter (as it is used less), so call the former in the rest of the users. Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: William Hubbs <w.d.hubbs@gmail.com> Cc: Chris Brannon <chris@the-brannons.com> Cc: Kirk Reiser <kirk@reisers.ca> Cc: Samuel Thibault <samuel.thibault@ens-lyon.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Reviewed-by: Johan Hovold <johan@kernel.org> Signed-off-by: Jiri Slaby <jslaby@suse.cz> Link: https://lore.kernel.org/r/20211122111648.30379-3-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit b68b914494df4f79b4e9b58953110574af1cb7a2 upstream.

Since commit a9c3f68f3cd8d (tty: Fix low_latency BUG) in 2014,
tty_flip_buffer_push() is only a wrapper to tty_schedule_flip(). We are
going to remove the latter (as it is used less), so call the former in
the rest of the users.

Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: William Hubbs <w.d.hubbs@gmail.com>
Cc: Chris Brannon <chris@the-brannons.com>
Cc: Kirk Reiser <kirk@reisers.ca>
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20211122111648.30379-3-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
alpha: Send stop IPI to send to online CPUs 2021-08-12T11:21:05+00:00 Prarit Bhargava prarit@redhat.com 2021-01-05T15:16:27+00:00 742e85fa9e802bf611ce645caa1c39bdd0a1d2a8 [ Upstream commit caace6ca4e06f09413fb8f8a63319594cfb7d47d ] This issue was noticed while debugging a shutdown issue where some secondary CPUs are not being shutdown correctly. A fix for that [1] requires that secondary cpus be offlined using the cpu_online_mask so that the stop operation is a no-op if CPU HOTPLUG is disabled. I, like the author in [1] looked at the architectures and found that alpha is one of two architectures that executes smp_send_stop() on all possible CPUs. On alpha, smp_send_stop() sends an IPI to all possible CPUs but only needs to send them to online CPUs. Send the stop IPI to only the online CPUs. [1] https://lkml.org/lkml/2020/1/10/250 Signed-off-by: Prarit Bhargava <prarit@redhat.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Signed-off-by: Matt Turner <mattst88@gmail.com> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit caace6ca4e06f09413fb8f8a63319594cfb7d47d ]

This issue was noticed while debugging a shutdown issue where some
secondary CPUs are not being shutdown correctly.  A fix for that [1] requires
that secondary cpus be offlined using the cpu_online_mask so that the
stop operation is a no-op if CPU HOTPLUG is disabled.  I, like the author in
[1] looked at the architectures and found that alpha is one of two
architectures that executes smp_send_stop() on all possible CPUs.

On alpha, smp_send_stop() sends an IPI to all possible CPUs but only needs
to send them to online CPUs.

Send the stop IPI to only the online CPUs.

[1] https://lkml.org/lkml/2020/1/10/250

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
alpha: fix memory barriers so that they conform to the specification 2020-06-22T07:31:21+00:00 Mikulas Patocka mpatocka@redhat.com 2020-05-26T14:47:49+00:00 c81e34c4346f9d3ba21a3c6f7491a6e7e330a7ee commit 54505a1e2083fc54cbe8779b97479f969cd30a00 upstream. The commits cd0e00c10672 and 92d7223a7423 broke boot on the Alpha Avanti platform. The patches move memory barriers after a write before the write. The result is that if there's iowrite followed by ioread, there is no barrier between them. The Alpha architecture allows reordering of the accesses to the I/O space, and the missing barrier between write and read causes hang with serial port and real time clock. This patch makes barriers confiorm to the specification. 1. We add mb() before readX_relaxed and writeX_relaxed - memory-barriers.txt claims that these functions must be ordered w.r.t. each other. Alpha doesn't order them, so we need an explicit barrier. 2. We add mb() before reads from the I/O space - so that if there's a write followed by a read, there should be a barrier between them. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Fixes: cd0e00c10672 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering") Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2") Cc: stable@vger.kernel.org # v4.17+ Acked-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Reviewed-by: Maciej W. Rozycki <macro@linux-mips.org> Signed-off-by: Matt Turner <mattst88@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 54505a1e2083fc54cbe8779b97479f969cd30a00 upstream.

The commits cd0e00c10672 and 92d7223a7423 broke boot on the Alpha Avanti
platform. The patches move memory barriers after a write before the write.
The result is that if there's iowrite followed by ioread, there is no
barrier between them.

The Alpha architecture allows reordering of the accesses to the I/O space,
and the missing barrier between write and read causes hang with serial
port and real time clock.

This patch makes barriers confiorm to the specification.

1. We add mb() before readX_relaxed and writeX_relaxed -
   memory-barriers.txt claims that these functions must be ordered w.r.t.
   each other. Alpha doesn't order them, so we need an explicit barrier.
2. We add mb() before reads from the I/O space - so that if there's a
   write followed by a read, there should be a barrier between them.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: cd0e00c10672 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering")
Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2")
Cc: stable@vger.kernel.org      # v4.17+
Acked-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Reviewed-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
dma-mapping: explicitly wire up ->mmap and ->get_sgtable 2019-09-04T09:13:18+00:00 Christoph Hellwig hch@lst.de 2019-08-06T12:01:50+00:00 f9f3232a7d0ab73a33d11f4056c5823010f03d55 While the default ->mmap and ->get_sgtable implementations work for the majority of our dma_map_ops impementations they are inherently safe for others that don't use the page allocator or CMA and/or use their own way of remapping not covered by the common code. So remove the defaults if these methods are not wired up, but instead wire up the default implementations for all safe instances. Fixes: e1c7e324539a ("dma-mapping: always provide the dma_map_ops based implementation") Signed-off-by: Christoph Hellwig <hch@lst.de> 
While the default ->mmap and ->get_sgtable implementations work for the
majority of our dma_map_ops impementations they are inherently safe
for others that don't use the page allocator or CMA and/or use their
own way of remapping not covered by the common code.  So remove the
defaults if these methods are not wired up, but instead wire up the
default implementations for all safe instances.

Fixes: e1c7e324539a ("dma-mapping: always provide the dma_map_ops based implementation")
Signed-off-by: Christoph Hellwig <hch@lst.de>
arch: mark syscall number 435 reserved for clone3 2019-07-14T22:39:33+00:00 Christian Brauner christian@brauner.io 2019-07-14T19:22:04+00:00 1a271a68e030f3e134de12087117574a883e20f0 A while ago Arnd made it possible to give new system calls the same syscall number on all architectures (except alpha). To not break this nice new feature let's mark 435 for clone3 as reserved on all architectures that do not yet implement it. Even if an architecture does not plan to implement it this ensures that new system calls coming after clone3 will have the same number on all architectures. Signed-off-by: Christian Brauner <christian@brauner.io> Cc: linux-arch@vger.kernel.org Cc: linux-alpha@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-ia64@vger.kernel.org Cc: linux-m68k@lists.linux-m68k.org Cc: linux-mips@vger.kernel.org Cc: linux-parisc@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Cc: linux-s390@vger.kernel.org Cc: linux-sh@vger.kernel.org Cc: sparclinux@vger.kernel.org Link: https://lore.kernel.org/r/20190714192205.27190-2-christian@brauner.io Reviewed-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Christian Brauner <christian@brauner.io> 
A while ago Arnd made it possible to give new system calls the same
syscall number on all architectures (except alpha). To not break this
nice new feature let's mark 435 for clone3 as reserved on all
architectures that do not yet implement it.
Even if an architecture does not plan to implement it this ensures that
new system calls coming after clone3 will have the same number on all
architectures.

Signed-off-by: Christian Brauner <christian@brauner.io>
Cc: linux-arch@vger.kernel.org
Cc: linux-alpha@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-m68k@lists.linux-m68k.org
Cc: linux-mips@vger.kernel.org
Cc: linux-parisc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: linux-sh@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Link: https://lore.kernel.org/r/20190714192205.27190-2-christian@brauner.io
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Christian Brauner <christian@brauner.io>
Merge tag 'pidfd-updates-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux 2019-07-11T05:17:21+00:00 Linus Torvalds torvalds@linux-foundation.org 2019-07-11T05:17:21+00:00 5450e8a316a64cddcbc15f90733ebc78aa736545 Pull pidfd updates from Christian Brauner: "This adds two main features. - First, it adds polling support for pidfds. This allows process managers to know when a (non-parent) process dies in a race-free way. The notification mechanism used follows the same logic that is currently used when the parent of a task is notified of a child's death. With this patchset it is possible to put pidfds in an {e}poll loop and get reliable notifications for process (i.e. thread-group) exit. - The second feature compliments the first one by making it possible to retrieve pollable pidfds for processes that were not created using CLONE_PIDFD. A lot of processes get created with traditional PID-based calls such as fork() or clone() (without CLONE_PIDFD). For these processes a caller can currently not create a pollable pidfd. This is a problem for Android's low memory killer (LMK) and service managers such as systemd. Both patchsets are accompanied by selftests. It's perhaps worth noting that the work done so far and the work done in this branch for pidfd_open() and polling support do already see some adoption: - Android is in the process of backporting this work to all their LTS kernels [1] - Service managers make use of pidfd_send_signal but will need to wait until we enable waiting on pidfds for full adoption. - And projects I maintain make use of both pidfd_send_signal and CLONE_PIDFD [2] and will use polling support and pidfd_open() too" [1] https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.9+backport%22 https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.14+backport%22 https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.19+backport%22 [2] https://github.com/lxc/lxc/blob/aab6e3eb73c343231cdde775db938994fc6f2803/src/lxc/start.c#L1753 * tag 'pidfd-updates-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: tests: add pidfd_open() tests arch: wire-up pidfd_open() pid: add pidfd_open() pidfd: add polling selftests pidfd: add polling support 
Pull pidfd updates from Christian Brauner:
 "This adds two main features.

   - First, it adds polling support for pidfds. This allows process
     managers to know when a (non-parent) process dies in a race-free
     way.

     The notification mechanism used follows the same logic that is
     currently used when the parent of a task is notified of a child's
     death. With this patchset it is possible to put pidfds in an
     {e}poll loop and get reliable notifications for process (i.e.
     thread-group) exit.

   - The second feature compliments the first one by making it possible
     to retrieve pollable pidfds for processes that were not created
     using CLONE_PIDFD.

     A lot of processes get created with traditional PID-based calls
     such as fork() or clone() (without CLONE_PIDFD). For these
     processes a caller can currently not create a pollable pidfd. This
     is a problem for Android's low memory killer (LMK) and service
     managers such as systemd.

  Both patchsets are accompanied by selftests.

  It's perhaps worth noting that the work done so far and the work done
  in this branch for pidfd_open() and polling support do already see
  some adoption:

   - Android is in the process of backporting this work to all their LTS
     kernels [1]

   - Service managers make use of pidfd_send_signal but will need to
     wait until we enable waiting on pidfds for full adoption.

   - And projects I maintain make use of both pidfd_send_signal and
     CLONE_PIDFD [2] and will use polling support and pidfd_open() too"

[1] https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.9+backport%22
    https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.14+backport%22
    https://android-review.googlesource.com/q/topic:%22pidfd+polling+support+4.19+backport%22

[2] https://github.com/lxc/lxc/blob/aab6e3eb73c343231cdde775db938994fc6f2803/src/lxc/start.c#L1753

* tag 'pidfd-updates-v5.3' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  tests: add pidfd_open() tests
  arch: wire-up pidfd_open()
  pid: add pidfd_open()
  pidfd: add polling selftests
  pidfd: add polling support