<feed xmlns='http://www.w3.org/2005/Atom'>
<title>user/sven/linux.git/include, branch v6.6.102</title>
<subtitle>Linux Kernel
</subtitle>
<id>https://git.stealer.net/cgit.cgi/user/sven/linux.git/atom?h=v6.6.102</id>
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<updated>2025-08-15T10:09:07Z</updated>
<entry>
<title>net: usbnet: Avoid potential RCU stall on LINK_CHANGE event</title>
<updated>2025-08-15T10:09:07Z</updated>
<author>
<name>John Ernberg</name>
<email>john.ernberg@actia.se</email>
</author>
<published>2025-07-23T10:25:35Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=3c6236588dc855807cf7c66545ff30b945fa7077'/>
<id>urn:sha1:3c6236588dc855807cf7c66545ff30b945fa7077</id>
<content type='text'>
commit 0d9cfc9b8cb17dbc29a98792d36ec39a1cf1395f upstream.

The Gemalto Cinterion PLS83-W modem (cdc_ether) is emitting confusing link
up and down events when the WWAN interface is activated on the modem-side.

Interrupt URBs will in consecutive polls grab:
* Link Connected
* Link Disconnected
* Link Connected

Where the last Connected is then a stable link state.

When the system is under load this may cause the unlink_urbs() work in
__handle_link_change() to not complete before the next usbnet_link_change()
call turns the carrier on again, allowing rx_submit() to queue new SKBs.

In that event the URB queue is filled faster than it can drain, ending up
in a RCU stall:

    rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: { 0-.... } 33108 jiffies s: 201 root: 0x1/.
    rcu: blocking rcu_node structures (internal RCU debug):
    Sending NMI from CPU 1 to CPUs 0:
    NMI backtrace for cpu 0

    Call trace:
     arch_local_irq_enable+0x4/0x8
     local_bh_enable+0x18/0x20
     __netdev_alloc_skb+0x18c/0x1cc
     rx_submit+0x68/0x1f8 [usbnet]
     rx_alloc_submit+0x4c/0x74 [usbnet]
     usbnet_bh+0x1d8/0x218 [usbnet]
     usbnet_bh_tasklet+0x10/0x18 [usbnet]
     tasklet_action_common+0xa8/0x110
     tasklet_action+0x2c/0x34
     handle_softirqs+0x2cc/0x3a0
     __do_softirq+0x10/0x18
     ____do_softirq+0xc/0x14
     call_on_irq_stack+0x24/0x34
     do_softirq_own_stack+0x18/0x20
     __irq_exit_rcu+0xa8/0xb8
     irq_exit_rcu+0xc/0x30
     el1_interrupt+0x34/0x48
     el1h_64_irq_handler+0x14/0x1c
     el1h_64_irq+0x68/0x6c
     _raw_spin_unlock_irqrestore+0x38/0x48
     xhci_urb_dequeue+0x1ac/0x45c [xhci_hcd]
     unlink1+0xd4/0xdc [usbcore]
     usb_hcd_unlink_urb+0x70/0xb0 [usbcore]
     usb_unlink_urb+0x24/0x44 [usbcore]
     unlink_urbs.constprop.0.isra.0+0x64/0xa8 [usbnet]
     __handle_link_change+0x34/0x70 [usbnet]
     usbnet_deferred_kevent+0x1c0/0x320 [usbnet]
     process_scheduled_works+0x2d0/0x48c
     worker_thread+0x150/0x1dc
     kthread+0xd8/0xe8
     ret_from_fork+0x10/0x20

Get around the problem by delaying the carrier on to the scheduled work.

This needs a new flag to keep track of the necessary action.

The carrier ok check cannot be removed as it remains required for the
LINK_RESET event flow.

Fixes: 4b49f58fff00 ("usbnet: handle link change")
Cc: stable@vger.kernel.org
Signed-off-by: John Ernberg &lt;john.ernberg@actia.se&gt;
Link: https://patch.msgid.link/20250723102526.1305339-1-john.ernberg@actia.se
Signed-off-by: Jakub Kicinski &lt;kuba@kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>sched/core: Remove ifdeffery for saved_state</title>
<updated>2025-08-15T10:09:07Z</updated>
<author>
<name>Elliot Berman</name>
<email>quic_eberman@quicinc.com</email>
</author>
<published>2023-09-08T22:49:15Z</published>
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<id>urn:sha1:8afa818c77330fcb269c77540b268f199d84ee8e</id>
<content type='text'>
commit fbaa6a181a4b1886cbf4214abdf9a2df68471510 upstream.

In preparation for freezer to also use saved_state, remove the
CONFIG_PREEMPT_RT compilation guard around saved_state.

On the arm64 platform I tested which did not have CONFIG_PREEMPT_RT,
there was no statistically significant deviation by applying this patch.

Test methodology:

perf bench sched message -g 40 -l 40

Signed-off-by: Elliot Berman &lt;quic_eberman@quicinc.com&gt;
Signed-off-by: Peter Zijlstra (Intel) &lt;peterz@infradead.org&gt;
Signed-off-by: Ingo Molnar &lt;mingo@kernel.org&gt;
Signed-off-by: Chen Ridong &lt;chenridong@huawei.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>net: drop UFO packets in udp_rcv_segment()</title>
<updated>2025-08-15T10:09:02Z</updated>
<author>
<name>Wang Liang</name>
<email>wangliang74@huawei.com</email>
</author>
<published>2025-07-30T10:14:58Z</published>
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<id>urn:sha1:0d45954034f8edd6d4052e0190d3d6335c37e4de</id>
<content type='text'>
[ Upstream commit d46e51f1c78b9ab9323610feb14238d06d46d519 ]

When sending a packet with virtio_net_hdr to tun device, if the gso_type
in virtio_net_hdr is SKB_GSO_UDP and the gso_size is less than udphdr
size, below crash may happen.

  ------------[ cut here ]------------
  kernel BUG at net/core/skbuff.c:4572!
  Oops: invalid opcode: 0000 [#1] SMP NOPTI
  CPU: 0 UID: 0 PID: 62 Comm: mytest Not tainted 6.16.0-rc7 #203 PREEMPT(voluntary)
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  RIP: 0010:skb_pull_rcsum+0x8e/0xa0
  Code: 00 00 5b c3 cc cc cc cc 8b 93 88 00 00 00 f7 da e8 37 44 38 00 f7 d8 89 83 88 00 00 00 48 8b 83 c8 00 00 00 5b c3 cc cc cc cc &lt;0f&gt; 0b 0f 0b 66 66 2e 0f 1f 84 00 000
  RSP: 0018:ffffc900001fba38 EFLAGS: 00000297
  RAX: 0000000000000004 RBX: ffff8880040c1000 RCX: ffffc900001fb948
  RDX: ffff888003e6d700 RSI: 0000000000000008 RDI: ffff88800411a062
  RBP: ffff8880040c1000 R08: 0000000000000000 R09: 0000000000000001
  R10: ffff888003606c00 R11: 0000000000000001 R12: 0000000000000000
  R13: ffff888004060900 R14: ffff888004050000 R15: ffff888004060900
  FS:  000000002406d3c0(0000) GS:ffff888084a19000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000020000040 CR3: 0000000004007000 CR4: 00000000000006f0
  Call Trace:
   &lt;TASK&gt;
   udp_queue_rcv_one_skb+0x176/0x4b0 net/ipv4/udp.c:2445
   udp_queue_rcv_skb+0x155/0x1f0 net/ipv4/udp.c:2475
   udp_unicast_rcv_skb+0x71/0x90 net/ipv4/udp.c:2626
   __udp4_lib_rcv+0x433/0xb00 net/ipv4/udp.c:2690
   ip_protocol_deliver_rcu+0xa6/0x160 net/ipv4/ip_input.c:205
   ip_local_deliver_finish+0x72/0x90 net/ipv4/ip_input.c:233
   ip_sublist_rcv_finish+0x5f/0x70 net/ipv4/ip_input.c:579
   ip_sublist_rcv+0x122/0x1b0 net/ipv4/ip_input.c:636
   ip_list_rcv+0xf7/0x130 net/ipv4/ip_input.c:670
   __netif_receive_skb_list_core+0x21d/0x240 net/core/dev.c:6067
   netif_receive_skb_list_internal+0x186/0x2b0 net/core/dev.c:6210
   napi_complete_done+0x78/0x180 net/core/dev.c:6580
   tun_get_user+0xa63/0x1120 drivers/net/tun.c:1909
   tun_chr_write_iter+0x65/0xb0 drivers/net/tun.c:1984
   vfs_write+0x300/0x420 fs/read_write.c:593
   ksys_write+0x60/0xd0 fs/read_write.c:686
   do_syscall_64+0x50/0x1c0 arch/x86/entry/syscall_64.c:63
   &lt;/TASK&gt;

To trigger gso segment in udp_queue_rcv_skb(), we should also set option
UDP_ENCAP_ESPINUDP to enable udp_sk(sk)-&gt;encap_rcv. When the encap_rcv
hook return 1 in udp_queue_rcv_one_skb(), udp_csum_pull_header() will try
to pull udphdr, but the skb size has been segmented to gso size, which
leads to this crash.

Previous commit cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
introduces segmentation in UDP receive path only for GRO, which was never
intended to be used for UFO, so drop UFO packets in udp_rcv_segment().

Link: https://lore.kernel.org/netdev/20250724083005.3918375-1-wangliang74@huawei.com/
Link: https://lore.kernel.org/netdev/20250729123907.3318425-1-wangliang74@huawei.com/
Fixes: cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
Suggested-by: Willem de Bruijn &lt;willemdebruijn.kernel@gmail.com&gt;
Signed-off-by: Wang Liang &lt;wangliang74@huawei.com&gt;
Reviewed-by: Willem de Bruijn &lt;willemb@google.com&gt;
Link: https://patch.msgid.link/20250730101458.3470788-1-wangliang74@huawei.com
Signed-off-by: Jakub Kicinski &lt;kuba@kernel.org&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>ipv6: reject malicious packets in ipv6_gso_segment()</title>
<updated>2025-08-15T10:09:02Z</updated>
<author>
<name>Eric Dumazet</name>
<email>edumazet@google.com</email>
</author>
<published>2025-07-30T13:17:38Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=ef05007b403dcc21e701cb1f30d4572ac0a9da20'/>
<id>urn:sha1:ef05007b403dcc21e701cb1f30d4572ac0a9da20</id>
<content type='text'>
[ Upstream commit d45cf1e7d7180256e17c9ce88e32e8061a7887fe ]

syzbot was able to craft a packet with very long IPv6 extension headers
leading to an overflow of skb-&gt;transport_header.

This 16bit field has a limited range.

Add skb_reset_transport_header_careful() helper and use it
from ipv6_gso_segment()

WARNING: CPU: 0 PID: 5871 at ./include/linux/skbuff.h:3032 skb_reset_transport_header include/linux/skbuff.h:3032 [inline]
WARNING: CPU: 0 PID: 5871 at ./include/linux/skbuff.h:3032 ipv6_gso_segment+0x15e2/0x21e0 net/ipv6/ip6_offload.c:151
Modules linked in:
CPU: 0 UID: 0 PID: 5871 Comm: syz-executor211 Not tainted 6.16.0-rc6-syzkaller-g7abc678e3084 #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
 RIP: 0010:skb_reset_transport_header include/linux/skbuff.h:3032 [inline]
 RIP: 0010:ipv6_gso_segment+0x15e2/0x21e0 net/ipv6/ip6_offload.c:151
Call Trace:
 &lt;TASK&gt;
  skb_mac_gso_segment+0x31c/0x640 net/core/gso.c:53
  nsh_gso_segment+0x54a/0xe10 net/nsh/nsh.c:110
  skb_mac_gso_segment+0x31c/0x640 net/core/gso.c:53
  __skb_gso_segment+0x342/0x510 net/core/gso.c:124
  skb_gso_segment include/net/gso.h:83 [inline]
  validate_xmit_skb+0x857/0x11b0 net/core/dev.c:3950
  validate_xmit_skb_list+0x84/0x120 net/core/dev.c:4000
  sch_direct_xmit+0xd3/0x4b0 net/sched/sch_generic.c:329
  __dev_xmit_skb net/core/dev.c:4102 [inline]
  __dev_queue_xmit+0x17b6/0x3a70 net/core/dev.c:4679

Fixes: d1da932ed4ec ("ipv6: Separate ipv6 offload support")
Reported-by: syzbot+af43e647fd835acc02df@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/688a1a05.050a0220.5d226.0008.GAE@google.com/T/#u
Signed-off-by: Eric Dumazet &lt;edumazet@google.com&gt;
Reviewed-by: Dawid Osuchowski &lt;dawid.osuchowski@linux.intel.com&gt;
Reviewed-by: Willem de Bruijn &lt;willemb@google.com&gt;
Link: https://patch.msgid.link/20250730131738.3385939-1-edumazet@google.com
Signed-off-by: Jakub Kicinski &lt;kuba@kernel.org&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>sched: Add test_and_clear_wake_up_bit() and atomic_dec_and_wake_up()</title>
<updated>2025-08-15T10:09:01Z</updated>
<author>
<name>NeilBrown</name>
<email>neilb@suse.de</email>
</author>
<published>2024-09-25T05:31:41Z</published>
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<id>urn:sha1:147216030e4655542cec362ea8322c8c6eb44f6b</id>
<content type='text'>
[ Upstream commit 52d633def56c10fe3e82a2c5d88c3ecb3f4e4852 ]

There are common patterns in the kernel of using test_and_clear_bit()
before wake_up_bit(), and atomic_dec_and_test() before wake_up_var().

These combinations don't need extra barriers but sometimes include them
unnecessarily.

To help avoid the unnecessary barriers and to help discourage the
general use of wake_up_bit/var (which is a fragile interface) introduce
two combined functions which implement these patterns.

Also add store_release_wake_up() which supports the task of simply
setting a non-atomic variable and sending a wakeup.  This pattern
requires barriers which are often omitted.

Signed-off-by: NeilBrown &lt;neilb@suse.de&gt;
Signed-off-by: Peter Zijlstra (Intel) &lt;peterz@infradead.org&gt;
Link: https://lore.kernel.org/r/20240925053405.3960701-5-neilb@suse.de
Stable-dep-of: 1db3a48e83bb ("NFS: Fix wakeup of __nfs_lookup_revalidate() in unblock_revalidate()")
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>module: Restore the moduleparam prefix length check</title>
<updated>2025-08-15T10:08:57Z</updated>
<author>
<name>Petr Pavlu</name>
<email>petr.pavlu@suse.com</email>
</author>
<published>2025-06-30T14:32:34Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=f9bd692540d8f94da87256d03be62895f73739a7'/>
<id>urn:sha1:f9bd692540d8f94da87256d03be62895f73739a7</id>
<content type='text'>
[ Upstream commit bdc877ba6b7ff1b6d2ebeff11e63da4a50a54854 ]

The moduleparam code allows modules to provide their own definition of
MODULE_PARAM_PREFIX, instead of using the default KBUILD_MODNAME ".".

Commit 730b69d22525 ("module: check kernel param length at compile time,
not runtime") added a check to ensure the prefix doesn't exceed
MODULE_NAME_LEN, as this is what param_sysfs_builtin() expects.

Later, commit 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking
for sysfs perms.") removed this check, but there is no indication this was
intentional.

Since the check is still useful for param_sysfs_builtin() to function
properly, reintroduce it in __module_param_call(), but in a modernized form
using static_assert().

While here, clean up the __module_param_call() comments. In particular,
remove the comment "Default value instead of permissions?", which comes
from commit 9774a1f54f17 ("[PATCH] Compile-time check re world-writeable
module params"). This comment was related to the test variable
__param_perm_check_##name, which was removed in the previously mentioned
commit 58f86cc89c33.

Fixes: 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking for sysfs perms.")
Signed-off-by: Petr Pavlu &lt;petr.pavlu@suse.com&gt;
Reviewed-by: Daniel Gomez &lt;da.gomez@samsung.com&gt;
Link: https://lore.kernel.org/r/20250630143535.267745-4-petr.pavlu@suse.com
Signed-off-by: Daniel Gomez &lt;da.gomez@samsung.com&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>proc: use the same treatment to check proc_lseek as ones for proc_read_iter et.al</title>
<updated>2025-08-15T10:08:54Z</updated>
<author>
<name>wangzijie</name>
<email>wangzijie1@honor.com</email>
</author>
<published>2025-06-07T02:13:53Z</published>
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<id>urn:sha1:33c778ea0bd0fa62ff590497e72562ff90f82b13</id>
<content type='text'>
[ Upstream commit ff7ec8dc1b646296f8d94c39339e8d3833d16c05 ]

Check pde-&gt;proc_ops-&gt;proc_lseek directly may cause UAF in rmmod scenario.
It's a gap in proc_reg_open() after commit 654b33ada4ab("proc: fix UAF in
proc_get_inode()").  Followed by AI Viro's suggestion, fix it in same
manner.

Link: https://lkml.kernel.org/r/20250607021353.1127963-1-wangzijie1@honor.com
Fixes: 3f61631d47f1 ("take care to handle NULL -&gt;proc_lseek()")
Signed-off-by: wangzijie &lt;wangzijie1@honor.com&gt;
Reviewed-by: Alexey Dobriyan &lt;adobriyan@gmail.com&gt;
Cc: Alexei Starovoitov &lt;ast@kernel.org&gt;
Cc: Al Viro &lt;viro@zeniv.linux.org.uk&gt;
Cc: "Edgecombe, Rick P" &lt;rick.p.edgecombe@intel.com&gt;
Cc: Kirill A. Shuemov &lt;kirill.shutemov@linux.intel.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>Bluetooth: hci_event: Mask data status from LE ext adv reports</title>
<updated>2025-08-15T10:08:49Z</updated>
<author>
<name>Chris Down</name>
<email>chris@chrisdown.name</email>
</author>
<published>2025-07-21T15:30:23Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=9d5aecb57e938595321e651c7c0c45398d79f731'/>
<id>urn:sha1:9d5aecb57e938595321e651c7c0c45398d79f731</id>
<content type='text'>
[ Upstream commit 0cadf8534f2a727bc3a01e8c583b085d25963ee0 ]

The Event_Type field in an LE Extended Advertising Report uses bits 5
and 6 for data status (e.g. truncation or fragmentation), not the PDU
type itself.

The ext_evt_type_to_legacy() function fails to mask these status bits
before evaluation. This causes valid advertisements with status bits set
(e.g. a truncated non-connectable advertisement, which ends up showing
as PDU type 0x40) to be misclassified as unknown and subsequently
dropped. This is okay for most checks which use bitwise AND on the
relevant event type bits, but it doesn't work for non-connectable types,
which are checked with '== LE_EXT_ADV_NON_CONN_IND' (that is, zero).

In terms of behaviour, first the device sends a truncated report:

&gt; HCI Event: LE Meta Event (0x3e) plen 26
      LE Extended Advertising Report (0x0d)
        Entry 0
          Event type: 0x0040
            Data status: Incomplete, data truncated, no more to come
          Address type: Random (0x01)
          Address: 1D:12:46:FA:F8:6E (Non-Resolvable)
          SID: 0x03
          RSSI: -98 dBm (0x9e)
          Data length: 0x00

Then, a few seconds later, it sends the subsequent complete report:

&gt; HCI Event: LE Meta Event (0x3e) plen 122
      LE Extended Advertising Report (0x0d)
        Entry 0
          Event type: 0x0000
            Data status: Complete
          Address type: Random (0x01)
          Address: 1D:12:46:FA:F8:6E (Non-Resolvable)
          SID: 0x03
          RSSI: -97 dBm (0x9f)
          Data length: 0x60
          Service Data: Google (0xfef3)
            Data[92]: ...

These devices often send multiple truncated reports per second.

This patch introduces a PDU type mask to ensure only the relevant bits
are evaluated, allowing for the correct translation of all valid
extended advertising packets.

Fixes: b2cc9761f144 ("Bluetooth: Handle extended ADV PDU types")
Signed-off-by: Chris Down &lt;chris@chrisdown.name&gt;
Signed-off-by: Luiz Augusto von Dentz &lt;luiz.von.dentz@intel.com&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>net_sched: act_ctinfo: use atomic64_t for three counters</title>
<updated>2025-08-15T10:08:47Z</updated>
<author>
<name>Eric Dumazet</name>
<email>edumazet@google.com</email>
</author>
<published>2025-07-09T09:01:57Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=c9eeae9639ea958fd14db33a2bcede94bf8c9248'/>
<id>urn:sha1:c9eeae9639ea958fd14db33a2bcede94bf8c9248</id>
<content type='text'>
[ Upstream commit d300335b4e18672913dd792ff9f49e6cccf41d26 ]

Commit 21c167aa0ba9 ("net/sched: act_ctinfo: use percpu stats")
missed that stats_dscp_set, stats_dscp_error and stats_cpmark_set
might be written (and read) locklessly.

Use atomic64_t for these three fields, I doubt act_ctinfo is used
heavily on big SMP hosts anyway.

Fixes: 24ec483cec98 ("net: sched: Introduce act_ctinfo action")
Signed-off-by: Eric Dumazet &lt;edumazet@google.com&gt;
Cc: Pedro Tammela &lt;pctammela@mojatatu.com&gt;
Link: https://patch.msgid.link/20250709090204.797558-6-edumazet@google.com
Signed-off-by: Jakub Kicinski &lt;kuba@kernel.org&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>sched/psi: Optimize psi_group_change() cpu_clock() usage</title>
<updated>2025-08-15T10:08:46Z</updated>
<author>
<name>Peter Zijlstra</name>
<email>peterz@infradead.org</email>
</author>
<published>2025-05-23T15:28:00Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=b1c6b13f48a8f5bf147e91e42da1db740b0a7b1f'/>
<id>urn:sha1:b1c6b13f48a8f5bf147e91e42da1db740b0a7b1f</id>
<content type='text'>
[ Upstream commit 570c8efd5eb79c3725ba439ce105ed1bedc5acd9 ]

Dietmar reported that commit 3840cbe24cf0 ("sched: psi: fix bogus
pressure spikes from aggregation race") caused a regression for him on
a high context switch rate benchmark (schbench) due to the now
repeating cpu_clock() calls.

In particular the problem is that get_recent_times() will extrapolate
the current state to 'now'. But if an update uses a timestamp from
before the start of the update, it is possible to get two reads
with inconsistent results. It is effectively back-dating an update.

(note that this all hard-relies on the clock being synchronized across
CPUs -- if this is not the case, all bets are off).

Combine this problem with the fact that there are per-group-per-cpu
seqcounts, the commit in question pushed the clock read into the group
iteration, causing tree-depth cpu_clock() calls. On architectures
where cpu_clock() has appreciable overhead, this hurts.

Instead move to a per-cpu seqcount, which allows us to have a single
clock read for all group updates, increasing internal consistency and
lowering update overhead. This comes at the cost of a longer update
side (proportional to the tree depth) which can cause the read side to
retry more often.

Fixes: 3840cbe24cf0 ("sched: psi: fix bogus pressure spikes from aggregation race")
Reported-by: Dietmar Eggemann &lt;dietmar.eggemann@arm.com&gt;
Signed-off-by: Peter Zijlstra (Intel) &lt;peterz@infradead.org&gt;
Acked-by: Johannes Weiner &lt;hannes@cmpxchg.org&gt;
Tested-by: Dietmar Eggemann &lt;dietmar.eggemann@arm.com&gt;,
Link: https://lkml.kernel.org/20250522084844.GC31726@noisy.programming.kicks-ass.net
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
</feed>
