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Now that all bits and pieces are in place, hook the RSEQ handling fast path
function into exit_to_user_mode_prepare() after the TIF work bits have been
handled. If case of fast path failure, TIF_NOTIFY_RESUME has been raised
and the caller needs to take another turn through the TIF handling slow
path.
This only works for architectures which use the generic entry code.
Architectures who still have their own incomplete hacks are not supported
and won't be.
This results in the following improvements:
Kernel build Before After Reduction
exit to user 80692981 80514451
signal checks: 32581 121 99%
slowpath runs: 1201408 1.49% 198 0.00% 100%
fastpath runs: 675941 0.84% N/A
id updates: 1233989 1.53% 50541 0.06% 96%
cs checks: 1125366 1.39% 0 0.00% 100%
cs cleared: 1125366 100% 0 100%
cs fixup: 0 0% 0
RSEQ selftests Before After Reduction
exit to user: 386281778 387373750
signal checks: 35661203 0 100%
slowpath runs: 140542396 36.38% 100 0.00% 100%
fastpath runs: 9509789 2.51% N/A
id updates: 176203599 45.62% 9087994 2.35% 95%
cs checks: 175587856 45.46% 4728394 1.22% 98%
cs cleared: 172359544 98.16% 1319307 27.90% 99%
cs fixup: 3228312 1.84% 3409087 72.10%
The 'cs cleared' and 'cs fixup' percentages are not relative to the exit to
user invocations, they are relative to the actual 'cs check' invocations.
While some of this could have been avoided in the original code, like the
obvious clearing of CS when it's already clear, the main problem of going
through TIF_NOTIFY_RESUME cannot be solved. In some workloads the RSEQ
notify handler is invoked more than once before going out to user
space. Doing this once when everything has stabilized is the only solution
to avoid this.
The initial attempt to completely decouple it from the TIF work turned out
to be suboptimal for workloads, which do a lot of quick and short system
calls. Even if the fast path decision is only 4 instructions (including a
conditional branch), this adds up quickly and becomes measurable when the
rate for actually having to handle rseq is in the low single digit
percentage range of user/kernel transitions.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251027084307.701201365@linutronix.de
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There is no point for this being visible in the resume_to_user_mode()
handling.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251027084306.211520245@linutronix.de
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We're trying to get sched.h down to more or less just types only, not
code - rseq can live in its own header.
This helps us kill the dependency on preempt.h in sched.h.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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Breno and Josef report a deadlock scenario from cgroup reclaim
re-entering the filesystem:
[ 361.546690] ======================================================
[ 361.559210] WARNING: possible circular locking dependency detected
[ 361.571703] 6.5.0-0_fbk700_debug_rc0_kbuilder_13159_gbf787a128001 #1 Tainted: G S E
[ 361.589704] ------------------------------------------------------
[ 361.602277] find/9315 is trying to acquire lock:
[ 361.611625] ffff88837ba140c0 (&delayed_node->mutex){+.+.}-{4:4}, at: __btrfs_release_delayed_node+0x68/0x4f0
[ 361.631437]
[ 361.631437] but task is already holding lock:
[ 361.643243] ffff8881765b8678 (btrfs-tree-01){++++}-{4:4}, at: btrfs_tree_read_lock+0x1e/0x40
[ 362.904457] mutex_lock_nested+0x1c/0x30
[ 362.912414] __btrfs_release_delayed_node+0x68/0x4f0
[ 362.922460] btrfs_evict_inode+0x301/0x770
[ 362.982726] evict+0x17c/0x380
[ 362.988944] prune_icache_sb+0x100/0x1d0
[ 363.005559] super_cache_scan+0x1f8/0x260
[ 363.013695] do_shrink_slab+0x2a2/0x540
[ 363.021489] shrink_slab_memcg+0x237/0x3d0
[ 363.050606] shrink_slab+0xa7/0x240
[ 363.083382] shrink_node_memcgs+0x262/0x3b0
[ 363.091870] shrink_node+0x1a4/0x720
[ 363.099150] shrink_zones+0x1f6/0x5d0
[ 363.148798] do_try_to_free_pages+0x19b/0x5e0
[ 363.157633] try_to_free_mem_cgroup_pages+0x266/0x370
[ 363.190575] reclaim_high+0x16f/0x1f0
[ 363.208409] mem_cgroup_handle_over_high+0x10b/0x270
[ 363.246678] try_charge_memcg+0xaf2/0xc70
[ 363.304151] charge_memcg+0xf0/0x350
[ 363.320070] __mem_cgroup_charge+0x28/0x40
[ 363.328371] __filemap_add_folio+0x870/0xd50
[ 363.371303] filemap_add_folio+0xdd/0x310
[ 363.399696] __filemap_get_folio+0x2fc/0x7d0
[ 363.419086] pagecache_get_page+0xe/0x30
[ 363.427048] alloc_extent_buffer+0x1cd/0x6a0
[ 363.435704] read_tree_block+0x43/0xc0
[ 363.443316] read_block_for_search+0x361/0x510
[ 363.466690] btrfs_search_slot+0xc8c/0x1520
This is caused by the mem_cgroup_handle_over_high() not respecting the
gfp_mask of the allocation context. We used to only call this function on
resume to userspace, where no locks were held. But c9afe31ec443 ("memcg:
synchronously enforce memory.high for large overcharges") added a call
from the allocation context without considering the gfp.
Link: https://lkml.kernel.org/r/20230914152139.100822-1-hannes@cmpxchg.org
Fixes: c9afe31ec443 ("memcg: synchronously enforce memory.high for large overcharges")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Breno Leitao <leitao@debian.org>
Reported-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: <stable@vger.kernel.org> [5.17+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Move set_notify_resume and tracehook_notify_resume into resume_user_mode.h.
While doing that rename tracehook_notify_resume to resume_user_mode_work.
Update all of the places that included tracehook.h for these functions to
include resume_user_mode.h instead.
Update all of the callers of tracehook_notify_resume to call
resume_user_mode_work.
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20220309162454.123006-12-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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