Merge tag 'threads-v5.6' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner...

Pull thread management updates from Christian Brauner:
 "Sargun Dhillon over the last cycle has worked on the pidfd_getfd()
  syscall.

  This syscall allows for the retrieval of file descriptors of a process
  based on its pidfd. A task needs to have ptrace_may_access()
  permissions with PTRACE_MODE_ATTACH_REALCREDS (suggested by Oleg and
  Andy) on the target.

  One of the main use-cases is in combination with seccomp's user
  notification feature. As a reminder, seccomp's user notification
  feature was made available in v5.0. It allows a task to retrieve a
  file descriptor for its seccomp filter. The file descriptor is usually
  handed of to a more privileged supervising process. The supervisor can
  then listen for syscall events caught by the seccomp filter of the
  supervisee and perform actions in lieu of the supervisee, usually
  emulating syscalls. pidfd_getfd() is needed to expand its uses.

  There are currently two major users that wait on pidfd_getfd() and one
  future user:

   - Netflix, Sargun said, is working on a service mesh where users
     should be able to connect to a dns-based VIP. When a user connects
     to e.g. 1.2.3.4:80 that runs e.g. service "foo" they will be
     redirected to an envoy process. This service mesh uses seccomp user
     notifications and pidfd to intercept all connect calls and instead
     of connecting them to 1.2.3.4:80 connects them to e.g.
     127.0.0.1:8080.

   - LXD uses the seccomp notifier heavily to intercept and emulate
     mknod() and mount() syscalls for unprivileged containers/processes.
     With pidfd_getfd() more uses-cases e.g. bridging socket connections
     will be possible.

   - The patchset has also seen some interest from the browser corner.
     Right now, Firefox is using a SECCOMP_RET_TRAP sandbox managed by a
     broker process. In the future glibc will start blocking all signals
     during dlopen() rendering this type of sandbox impossible. Hence,
     in the future Firefox will switch to a seccomp-user-nofication
     based sandbox which also makes use of file descriptor retrieval.
     The thread for this can be found at
     https://sourceware.org/ml/libc-alpha/2019-12/msg00079.html

  With pidfd_getfd() it is e.g. possible to bridge socket connections
  for the supervisee (binding to a privileged port) and taking actions
  on file descriptors on behalf of the supervisee in general.

  Sargun's first version was using an ioctl on pidfds but various people
  pushed for it to be a proper syscall which he duely implemented as
  well over various review cycles. Selftests are of course included.
  I've also added instructions how to deal with merge conflicts below.

  There's also a small fix coming from the kernel mentee project to
  correctly annotate struct sighand_struct with __rcu to fix various
  sparse warnings. We've received a few more such fixes and even though
  they are mostly trivial I've decided to postpone them until after -rc1
  since they came in rather late and I don't want to risk introducing
  build warnings.

  Finally, there's a new prctl() command PR_{G,S}ET_IO_FLUSHER which is
  needed to avoid allocation recursions triggerable by storage drivers
  that have userspace parts that run in the IO path (e.g. dm-multipath,
  iscsi, etc). These allocation recursions deadlock the device.

  The new prctl() allows such privileged userspace components to avoid
  allocation recursions by setting the PF_MEMALLOC_NOIO and
  PF_LESS_THROTTLE flags. The patch carries the necessary acks from the
  relevant maintainers and is routed here as part of prctl()
  thread-management."

* tag 'threads-v5.6' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  prctl: PR_{G,S}ET_IO_FLUSHER to support controlling memory reclaim
  sched.h: Annotate sighand_struct with __rcu
  test: Add test for pidfd getfd
  arch: wire up pidfd_getfd syscall
  pid: Implement pidfd_getfd syscall
  vfs, fdtable: Add fget_task helper

diff --cc arch/alpha/kernel/syscalls/syscall.tbl
index 4d7f2ff,8230108..36d42da
--- 1/arch/alpha/kernel/syscalls/syscall.tbl
--- 2/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@@ -475,4 -475,4 +475,5 @@@
  543   common  fspick                          sys_fspick
  544   common  pidfd_open                      sys_pidfd_open
  # 545 reserved for clone3
 +547   common  openat2                         sys_openat2
+ 548   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/arm/tools/syscall.tbl
index 4ba54bc,ba045e2..4d1cf74
--- 1/arch/arm/tools/syscall.tbl
--- 2/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@@ -449,4 -449,4 +449,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  435   common  clone3                          sys_clone3
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/arm64/include/asm/unistd.h
Simple merge

diff --cc arch/arm64/include/asm/unistd32.h
index 57f6f59,a8da97a..c1c6163
--- 1/arch/arm64/include/asm/unistd32.h
--- 2/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@@ -879,8 -879,8 +879,10 @@@ __SYSCALL(__NR_fspick, sys_fspick
  __SYSCALL(__NR_pidfd_open, sys_pidfd_open)
  #define __NR_clone3 435
  __SYSCALL(__NR_clone3, sys_clone3)
 +#define __NR_openat2 437
 +__SYSCALL(__NR_openat2, sys_openat2)
+ #define __NR_pidfd_getfd 438
+ __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
  
  /*
   * Please add new compat syscalls above this comment and update

diff --cc arch/ia64/kernel/syscalls/syscall.tbl
index 8d36f2e,2b11adf..042911e
--- 1/arch/ia64/kernel/syscalls/syscall.tbl
--- 2/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl
@@@ -356,4 -356,4 +356,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  # 435 reserved for clone3
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/m68k/kernel/syscalls/syscall.tbl
index b911e0f,44e879e..f4f49fc
--- 1/arch/m68k/kernel/syscalls/syscall.tbl
--- 2/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@@ -434,5 -434,5 +434,6 @@@
  432   common  fsmount                         sys_fsmount
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
 -# 435 reserved for clone3
 +435   common  clone3                          __sys_clone3
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/microblaze/kernel/syscalls/syscall.tbl
index c04385e,7afa001..4c67b11
--- 1/arch/microblaze/kernel/syscalls/syscall.tbl
--- 2/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@@ -441,4 -441,4 +441,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  435   common  clone3                          sys_clone3
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/mips/kernel/syscalls/syscall_n32.tbl
index 68c9ec0,856d5ba..1f9e8ad
--- 1/arch/mips/kernel/syscalls/syscall_n32.tbl
--- 2/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@@ -374,4 -374,4 +374,5 @@@
  433   n32     fspick                          sys_fspick
  434   n32     pidfd_open                      sys_pidfd_open
  435   n32     clone3                          __sys_clone3
 +437   n32     openat2                         sys_openat2
+ 438   n32     pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/mips/kernel/syscalls/syscall_n64.tbl
index 42a72d0,2db6075..c0b9d80
--- 1/arch/mips/kernel/syscalls/syscall_n64.tbl
--- 2/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@@ -350,4 -350,4 +350,5 @@@
  433   n64     fspick                          sys_fspick
  434   n64     pidfd_open                      sys_pidfd_open
  435   n64     clone3                          __sys_clone3
 +437   n64     openat2                         sys_openat2
+ 438   n64     pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/mips/kernel/syscalls/syscall_o32.tbl
index f114c4a,e9f9d4a..ac58677
--- 1/arch/mips/kernel/syscalls/syscall_o32.tbl
--- 2/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@@ -423,4 -423,4 +423,5 @@@
  433   o32     fspick                          sys_fspick
  434   o32     pidfd_open                      sys_pidfd_open
  435   o32     clone3                          __sys_clone3
 +437   o32     openat2                         sys_openat2
+ 438   o32     pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/parisc/kernel/syscalls/syscall.tbl
index b550ae9,c58c7eb..52a15f5
--- 1/arch/parisc/kernel/syscalls/syscall.tbl
--- 2/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@@ -433,4 -433,4 +433,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  435   common  clone3                          sys_clone3_wrapper
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/powerpc/kernel/syscalls/syscall.tbl
index a8b5ecb,707609b..35b61bf
--- 1/arch/powerpc/kernel/syscalls/syscall.tbl
--- 2/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@@ -517,4 -517,4 +517,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  435   nospu   clone3                          ppc_clone3
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/s390/kernel/syscalls/syscall.tbl
index 16b571c,185cd62..bd7bd35
--- 1/arch/s390/kernel/syscalls/syscall.tbl
--- 2/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@@ -438,4 -438,4 +438,5 @@@
  433  common   fspick                  sys_fspick                      sys_fspick
  434  common   pidfd_open              sys_pidfd_open                  sys_pidfd_open
  435  common   clone3                  sys_clone3                      sys_clone3
 +437  common   openat2                 sys_openat2                     sys_openat2
+ 438  common   pidfd_getfd             sys_pidfd_getfd                 sys_pidfd_getfd

diff --cc arch/sh/kernel/syscalls/syscall.tbl
index a7185cc,88f9089..c7a30fc
--- 1/arch/sh/kernel/syscalls/syscall.tbl
--- 2/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@@ -438,4 -438,4 +438,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  # 435 reserved for clone3
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/sparc/kernel/syscalls/syscall.tbl
index b11c195,218df6a..f13615e
--- 1/arch/sparc/kernel/syscalls/syscall.tbl
--- 2/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@@ -481,4 -481,4 +481,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  # 435 reserved for clone3
 +437   common  openat2                 sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc arch/x86/entry/syscalls/syscall_32.tbl
index d22a8b5,9c3101b..c17cb77
--- 1/arch/x86/entry/syscalls/syscall_32.tbl
--- 2/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@@ -440,4 -440,4 +440,5 @@@
  433   i386    fspick                  sys_fspick                      __ia32_sys_fspick
  434   i386    pidfd_open              sys_pidfd_open                  __ia32_sys_pidfd_open
  435   i386    clone3                  sys_clone3                      __ia32_sys_clone3
 +437   i386    openat2                 sys_openat2                     __ia32_sys_openat2
+ 438   i386    pidfd_getfd             sys_pidfd_getfd                 __ia32_sys_pidfd_getfd

diff --cc arch/x86/entry/syscalls/syscall_64.tbl
index 9035647,cef85db..44d510b
--- 1/arch/x86/entry/syscalls/syscall_64.tbl
--- 2/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@@ -357,7 -357,7 +357,8 @@@
  433   common  fspick                  __x64_sys_fspick
  434   common  pidfd_open              __x64_sys_pidfd_open
  435   common  clone3                  __x64_sys_clone3/ptregs
 +437   common  openat2                 __x64_sys_openat2
+ 438   common  pidfd_getfd             __x64_sys_pidfd_getfd
  
  #
  # x32-specific system call numbers start at 512 to avoid cache impact

diff --cc arch/xtensa/kernel/syscalls/syscall.tbl
index f0a6801,ae15183..85a9ab1
--- 1/arch/xtensa/kernel/syscalls/syscall.tbl
--- 2/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@@ -406,4 -406,4 +406,5 @@@
  433   common  fspick                          sys_fspick
  434   common  pidfd_open                      sys_pidfd_open
  435   common  clone3                          sys_clone3
 +437   common  openat2                         sys_openat2
+ 438   common  pidfd_getfd                     sys_pidfd_getfd

diff --cc fs/file.c
Simple merge

diff --cc include/linux/sched.h
Simple merge

diff --cc include/linux/syscalls.h
Simple merge

diff --cc include/uapi/asm-generic/unistd.h
index d4122c0,d36ec3d..3a3201e
--- 1/include/uapi/asm-generic/unistd.h
--- 2/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@@ -850,12 -850,11 +850,14 @@@ __SYSCALL(__NR_pidfd_open, sys_pidfd_op
  #define __NR_clone3 435
  __SYSCALL(__NR_clone3, sys_clone3)
  #endif
 +
 +#define __NR_openat2 437
 +__SYSCALL(__NR_openat2, sys_openat2)
+ #define __NR_pidfd_getfd 438
+ __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
  
  #undef __NR_syscalls
- #define __NR_syscalls 438
+ #define __NR_syscalls 439
  
  /*
   * 32 bit systems traditionally used different