From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
To: "Liam R. Howlett" <liam@infradead.org>
Cc: Jann Horn <jannh@google.com>,
Alexei Starovoitov <alexei.starovoitov@gmail.com>,
bpf@vger.kernel.org, daniel@iogearbox.net, andrii@kernel.org,
eddyz87@gmail.com, memxor@gmail.com, oleg@redhat.com,
peterz@infradead.org, mhiramat@kernel.org, jolsa@kernel.org,
akpm@linux-foundation.org, surenb@google.com, david@kernel.org,
vbabka@kernel.org, hughd@google.com, kees@kernel.org,
mingo@redhat.com, tglx@kernel.org, x86@kernel.org,
linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next 4/9] uprobes/x86: Don't WARN if an optimized probe can't be written
Date: Fri, 23 Oct 2026 15:06:59 +0100 [thread overview]
Message-ID: <attpuy6TvlOgB7yJ@gremlin> (raw)
In-Reply-To: <dabdsge2cphfoulqobeswzj7xxkvlq2qyyi3iauqgmftfj6vg6@hbmosdt6t4bd>
On Thu, Oct 22, 2026 at 03:33:16PM -0400, Liam R. Howlett wrote:
> On 26/10/22 07:56PM, Jann Horn wrote:
> > On Thu, Oct 22, 2026 at 3:57 AM Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > > @@ -1197,7 +1194,7 @@ static int __arch_uprobe_optimize(struct arch_uprobe *auprobe, struct mm_struct
> > > if (IS_ERR(tramp))
> > > return PTR_ERR(tramp);
> > > ret = swbp_optimize(auprobe, vma, vaddr, tramp->vm_start);
> > > - if (WARN_ON_ONCE(ret) && new_mapping)
> > > + if (ret && new_mapping)
> > > WARN_ON_ONCE(do_munmap(mm, tramp->vm_start, PAGE_SIZE, NULL));
> >
> > Not an issue with your patch, just FYI regarding this preexisting
> > WARN_ON_ONCE():
> > A failing small GFP_KERNEL allocation could theoretically cause
> > do_munmap() to fail; the VMA tree has the ugly quirk that you can't
> > reliably _remove_ elements without memory allocation.
>
> During munmap() we may need an allocation of one or two vma(s)
> (splitting a vma or punching a hole) - and those may have anon vma
> chains that need to be allocated, we may need to allocate for uffd
> reasons, and we may need to allocate for the maple tree.
>
> That said, this path exclusively uses GFP_KERNEL which means we will
> invoke the shrinker. If the shrinker comes back unsuccessful, we will
> invoke OOM. This either succeed or it does not matter (we'll kill this
> task).
But you'd still get the WARN_ON() in the 'does not matter' case right?
>
> The other two possibilities is that the OOM is disabled during
> hibernate/suspend calls, or error injection caused the failure.
Fatal signals too?
Might be some other cases too there.
In general I'd say this WARN_ON() is probably not helpful.
--
Cheers, Lorenzo
next prev parent reply other threads:[~2026-10-23 14:07 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-22 1:57 [PATCH bpf-next 0/9] uprobes: Don't stall fork() when mmap_lock is busy Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 1/9] mm: Bring back mmap_write_trylock() Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 2/9] uprobes: Don't run exit_mmap() under dup_mmap_sem Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 3/9] uprobes/x86: Finish an unoptimization which failed half-way Alexei Starovoitov
2026-10-22 2:57 ` Gregory Price (Meta)
2026-10-23 7:13 ` Jiri Olsa
2026-10-22 1:57 ` [PATCH bpf-next 4/9] uprobes/x86: Don't WARN if an optimized probe can't be written Alexei Starovoitov
2026-10-22 2:37 ` bot+bpf-ci
2026-10-22 17:56 ` Jann Horn
2026-10-22 19:33 ` Liam R. Howlett
2026-10-23 14:06 ` Lorenzo Stoakes (ARM) [this message]
2026-10-23 7:13 ` Jiri Olsa
2026-10-22 1:57 ` [PATCH bpf-next 5/9] uprobes: Don't sleep on mmap_lock under dup_mmap_sem Alexei Starovoitov
2026-10-22 2:37 ` bot+bpf-ci
2026-10-22 23:11 ` Andrii Nakryiko
2026-10-22 1:57 ` [PATCH bpf-next 6/9] uprobes: Don't sleep on mmap_lock with dup_mmap_sem held in dup_mmap() Alexei Starovoitov
2026-10-22 18:42 ` Jann Horn
2026-10-22 1:57 ` [PATCH bpf-next 7/9] fork: Let the new task point to its mm before uprobes can find it Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 8/9] uprobes: Don't leak the breakpoints if the unregistering task is killed Alexei Starovoitov
2026-10-22 1:57 ` [PATCH bpf-next 9/9] selftests/bpf: Test uprobes and fork() with busy mmap_lock Alexei Starovoitov
2026-10-22 2:37 ` bot+bpf-ci
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