# git rev-parse -q --verify b4b27b9eed8ebdbf9f3046197d29d733c8c944f3^{commit}
b4b27b9eed8ebdbf9f3046197d29d733c8c944f3
already have revision, skipping fetch
# git checkout -q -f -B kisskb b4b27b9eed8ebdbf9f3046197d29d733c8c944f3
# git clean -qxdf
# < git log -1
# commit b4b27b9eed8ebdbf9f3046197d29d733c8c944f3
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Sun Jun 27 13:32:54 2021 -0700
# 
#     Revert "signal: Allow tasks to cache one sigqueue struct"
#     
#     This reverts commits 4bad58ebc8bc4f20d89cff95417c9b4674769709 (and
#     399f8dd9a866e107639eabd3c1979cd526ca3a98, which tried to fix it).
#     
#     I do not believe these are correct, and I'm about to release 5.13, so am
#     reverting them out of an abundance of caution.
#     
#     The locking is odd, and appears broken.
#     
#     On the allocation side (in __sigqueue_alloc()), the locking is somewhat
#     straightforward: it depends on sighand->siglock.  Since one caller
#     doesn't hold that lock, it further then tests 'sigqueue_flags' to avoid
#     the case with no locks held.
#     
#     On the freeing side (in sigqueue_cache_or_free()), there is no locking
#     at all, and the logic instead depends on 'current' being a single
#     thread, and not able to race with itself.
#     
#     To make things more exciting, there's also the data race between freeing
#     a signal and allocating one, which is handled by using WRITE_ONCE() and
#     READ_ONCE(), and being mutually exclusive wrt the initial state (ie
#     freeing will only free if the old state was NULL, while allocating will
#     obviously only use the value if it was non-NULL, so only one or the
#     other will actually act on the value).
#     
#     However, while the free->alloc paths do seem mutually exclusive thanks
#     to just the data value dependency, it's not clear what the memory
#     ordering constraints are on it.  Could writes from the previous
#     allocation possibly be delayed and seen by the new allocation later,
#     causing logical inconsistencies?
#     
#     So it's all very exciting and unusual.
#     
#     And in particular, it seems that the freeing side is incorrect in
#     depending on "current" being single-threaded.  Yes, 'current' is a
#     single thread, but in the presense of asynchronous events even a single
#     thread can have data races.
#     
#     And such asynchronous events can and do happen, with interrupts causing
#     signals to be flushed and thus free'd (for example - sending a
#     SIGCONT/SIGSTOP can happen from interrupt context, and can flush
#     previously queued process control signals).
#     
#     So regardless of all the other questions about the memory ordering and
#     locking for this new cached allocation, the sigqueue_cache_or_free()
#     assumptions seem to be fundamentally incorrect.
#     
#     It may be that people will show me the errors of my ways, and tell me
#     why this is all safe after all.  We can reinstate it if so.  But my
#     current belief is that the WRITE_ONCE() that sets the cached entry needs
#     to be a smp_store_release(), and the READ_ONCE() that finds a cached
#     entry needs to be a smp_load_acquire() to handle memory ordering
#     correctly.
#     
#     And the sequence in sigqueue_cache_or_free() would need to either use a
#     lock or at least be interrupt-safe some way (perhaps by using something
#     like the percpu 'cmpxchg': it doesn't need to be SMP-safe, but like the
#     percpu operations it needs to be interrupt-safe).
#     
#     Fixes: 399f8dd9a866 ("signal: Prevent sigqueue caching after task got released")
#     Fixes: 4bad58ebc8bc ("signal: Allow tasks to cache one sigqueue struct")
#     Cc: Thomas Gleixner <tglx@linutronix.de>
#     Cc: Peter Zijlstra <peterz@infradead.org>
#     Cc: Oleg Nesterov <oleg@redhat.com>
#     Cc: Christian Brauner <christian.brauner@ubuntu.com>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-gcc --version
# < /opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-ld --version
# < git log --format=%s --max-count=1 b4b27b9eed8ebdbf9f3046197d29d733c8c944f3
# < make -s -j 32 ARCH=xtensa O=/kisskb/build/linus_xtensa-allmodconfig_xtensa CROSS_COMPILE=/opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-  allmodconfig
# Added to kconfig CONFIG_BUILD_DOCSRC=n
# Added to kconfig CONFIG_MODULE_SIG=n
# Added to kconfig CONFIG_SAMPLES=n
# < make -s -j 32 ARCH=xtensa O=/kisskb/build/linus_xtensa-allmodconfig_xtensa CROSS_COMPILE=/opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-  help
# make -s -j 32 ARCH=xtensa O=/kisskb/build/linus_xtensa-allmodconfig_xtensa CROSS_COMPILE=/opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-  olddefconfig
# make -s -j 32 ARCH=xtensa O=/kisskb/build/linus_xtensa-allmodconfig_xtensa CROSS_COMPILE=/opt/cross/kisskb/br-xtensa-full-2016.08-613-ge98b4dd/bin/xtensa-linux-  
In file included from /kisskb/src/arch/xtensa/include/asm/atomic.h:19:0,
                 from /kisskb/src/include/linux/atomic.h:7,
                 from /kisskb/src/include/linux/page_counter.h:5,
                 from /kisskb/src/mm/memcontrol.c:28:
/kisskb/src/mm/memcontrol.c: In function 'memcg_reparent_objcgs':
/kisskb/src/arch/xtensa/include/asm/cmpxchg.h:173:3: warning: value computed is not used [-Wunused-value]
  ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
   ^
/kisskb/src/mm/memcontrol.c:334:2: note: in expansion of macro 'xchg'
  xchg(&objcg->memcg, parent);
  ^
/kisskb/src/arch/xtensa/include/asm/cmpxchg.h:173:3: warning: value computed is not used [-Wunused-value]
  ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
   ^
/kisskb/src/mm/memcontrol.c:341:3: note: in expansion of macro 'xchg'
   xchg(&iter->memcg, parent);
   ^
In file included from /kisskb/src/arch/xtensa/include/asm/atomic.h:19:0,
                 from /kisskb/src/include/linux/atomic.h:7,
                 from /kisskb/src/include/asm-generic/bitops/atomic.h:5,
                 from /kisskb/src/arch/xtensa/include/asm/bitops.h:192,
                 from /kisskb/src/include/linux/bitops.h:32,
                 from /kisskb/src/include/linux/kernel.h:12,
                 from /kisskb/src/include/linux/list.h:9,
                 from /kisskb/src/include/linux/wait.h:7,
                 from /kisskb/src/include/linux/wait_bit.h:8,
                 from /kisskb/src/include/linux/fs.h:6,
                 from /kisskb/src/fs/ocfs2/file.c:11:
/kisskb/src/fs/ocfs2/file.c: In function 'ocfs2_file_write_iter':
/kisskb/src/arch/xtensa/include/asm/cmpxchg.h:173:3: warning: value computed is not used [-Wunused-value]
  ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
   ^
/kisskb/src/fs/ocfs2/file.c:2468:3: note: in expansion of macro 'xchg'
   xchg(&iocb->ki_complete, saved_ki_complete);
   ^
/kisskb/src/drivers/gpu/drm/rockchip/cdn-dp-core.c:1124:12: warning: 'cdn_dp_resume' defined but not used [-Wunused-function]
 static int cdn_dp_resume(struct device *dev)
            ^
/kisskb/src/drivers/input/joystick/analog.c:160:2: warning: #warning Precise timer not defined for this architecture. [-Wcpp]
 #warning Precise timer not defined for this architecture.
  ^
In file included from /kisskb/src/arch/xtensa/include/asm/atomic.h:19:0,
                 from /kisskb/src/include/linux/atomic.h:7,
                 from /kisskb/src/include/asm-generic/bitops/atomic.h:5,
                 from /kisskb/src/arch/xtensa/include/asm/bitops.h:192,
                 from /kisskb/src/include/linux/bitops.h:32,
                 from /kisskb/src/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c:11:
/kisskb/src/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c: In function 'ixgbevf_xdp_setup':
/kisskb/src/arch/xtensa/include/asm/cmpxchg.h:173:3: warning: value computed is not used [-Wunused-value]
  ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))
   ^
/kisskb/src/drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c:4449:4: note: in expansion of macro 'xchg'
    xchg(&adapter->rx_ring[i]->xdp_prog, adapter->xdp_prog);
    ^
WARNING: modpost: lib/find_bit_benchmark.o(.text.unlikely+0x0): Section mismatch in reference from the (unknown reference) (unknown) to the variable .init.data:bitmap2
The function (unknown)() references
the variable __initdata bitmap2.
This is often because (unknown) lacks a __initdata 
annotation or the annotation of bitmap2 is wrong.

WARNING: modpost: lib/test_bitmap.o(.text.unlikely+0x58): Section mismatch in reference from the function bitmap_equal() to the variable .init.rodata:clump_exp
The function bitmap_equal() references
the variable __initconst clump_exp.
This is often because bitmap_equal lacks a __initconst 
annotation or the annotation of clump_exp is wrong.

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3570): Section mismatch in reference from the variable qed_mfw_legacy_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_legacy_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3588): Section mismatch in reference from the variable qed_mfw_legacy_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_legacy_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x35a0): Section mismatch in reference from the variable qed_mfw_legacy_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_legacy_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x35b8): Section mismatch in reference from the variable qed_mfw_legacy_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_legacy_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x35d0): Section mismatch in reference from the variable qed_mfw_legacy_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_legacy_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x35e8): Section mismatch in reference from the variable qed_mfw_legacy_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_legacy_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3600): Section mismatch in reference from the variable qed_mfw_legacy_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_legacy_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3618): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3630): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3648): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3660): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3678): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x3690): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x36a8): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x36c0): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qed/qed.o(.data+0x36d8): Section mismatch in reference from the variable qed_mfw_ext_maps to the variable .init.rodata:qed_mfw_legacy_bb_100g
The variable qed_mfw_ext_maps references
the variable __initconst qed_mfw_legacy_bb_100g
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qede/qede.o(.data+0x13c): Section mismatch in reference from the variable qede_forced_speed_maps to the variable .init.rodata:qede_forced_speed_100000
The variable qede_forced_speed_maps references
the variable __initconst qede_forced_speed_100000
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qede/qede.o(.data+0x154): Section mismatch in reference from the variable qede_forced_speed_maps to the variable .init.rodata:qede_forced_speed_100000
The variable qede_forced_speed_maps references
the variable __initconst qede_forced_speed_100000
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qede/qede.o(.data+0x16c): Section mismatch in reference from the variable qede_forced_speed_maps to the variable .init.rodata:qede_forced_speed_100000
The variable qede_forced_speed_maps references
the variable __initconst qede_forced_speed_100000
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qede/qede.o(.data+0x184): Section mismatch in reference from the variable qede_forced_speed_maps to the variable .init.rodata:qede_forced_speed_100000
The variable qede_forced_speed_maps references
the variable __initconst qede_forced_speed_100000
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qede/qede.o(.data+0x19c): Section mismatch in reference from the variable qede_forced_speed_maps to the variable .init.rodata:qede_forced_speed_100000
The variable qede_forced_speed_maps references
the variable __initconst qede_forced_speed_100000
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qede/qede.o(.data+0x1b4): Section mismatch in reference from the variable qede_forced_speed_maps to the variable .init.rodata:qede_forced_speed_100000
The variable qede_forced_speed_maps references
the variable __initconst qede_forced_speed_100000
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

WARNING: modpost: drivers/net/ethernet/qlogic/qede/qede.o(.data+0x1cc): Section mismatch in reference from the variable qede_forced_speed_maps to the variable .init.rodata:qede_forced_speed_100000
The variable qede_forced_speed_maps references
the variable __initconst qede_forced_speed_100000
If the reference is valid then annotate the
variable with __init* or __refdata (see linux/init.h) or name the variable:
*_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console

Completed OK
# rm -rf /kisskb/build/linus_xtensa-allmodconfig_xtensa
# Build took: 0:17:54.573333