From: Matthew Wilcox <willy@infradead.org>
To: Qian Cai <cai@lca.pw>
Cc: akpm@linux-foundation.org, dennis@kernel.org, tj@kernel.org,
cl@linux.com, elver@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/util: fix a data race in __vm_enough_memory()
Date: Wed, 29 Jan 2020 20:20:11 -0800 [thread overview]
Message-ID: <20200130042011.GI6615@bombadil.infradead.org> (raw)
In-Reply-To: <20200130025133.5232-1-cai@lca.pw>
On Wed, Jan 29, 2020 at 09:51:33PM -0500, Qian Cai wrote:
> "vm_committed_as.count" could be accessed concurrently as reported by
> KCSAN,
>
> read to 0xffffffff923164f8 of 8 bytes by task 1268 on cpu 38:
> __vm_enough_memory+0x43/0x280 mm/util.c:801
> mmap_region+0x1b2/0xb90 mm/mmap.c:1726
> do_mmap+0x45c/0x700
> vm_mmap_pgoff+0xc0/0x130
> vm_mmap+0x71/0x90
> elf_map+0xa1/0x1b0
> load_elf_binary+0x9de/0x2180
> search_binary_handler+0xd8/0x2b0
> __do_execve_file+0xb61/0x1080
> __x64_sys_execve+0x5f/0x70
> do_syscall_64+0x91/0xb47
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> write to 0xffffffff923164f8 of 8 bytes by task 1265 on cpu 41:
> percpu_counter_add_batch+0x83/0xd0 lib/percpu_counter.c:91
> exit_mmap+0x178/0x220 include/linux/mman.h:68
> mmput+0x10e/0x270
> flush_old_exec+0x572/0xfe0
> load_elf_binary+0x467/0x2180
> search_binary_handler+0xd8/0x2b0
> __do_execve_file+0xb61/0x1080
> __x64_sys_execve+0x5f/0x70
> do_syscall_64+0x91/0xb47
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Since only the read is operating as lockless, fix it by using
> READ_ONLY() for it to avoid any possible false warning due to load
You mean READ_ONCE ...
> {
> long allowed;
>
> - VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) <
> + VM_WARN_ONCE(READ_ONCE(vm_committed_as.count) <
> -(s64)vm_committed_as_batch * num_online_cpus(),
I'm really not a fan of exposing the internals of a percpu_counter outside
the percpu_counter.h file. Why shouldn't this be fixed by putting the
READ_ONCE() inside percpu_counter_read()?
next prev parent reply other threads:[~2020-01-30 4:20 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-30 2:51 [PATCH] mm/util: fix a data race in __vm_enough_memory() Qian Cai
2020-01-30 4:20 ` Matthew Wilcox [this message]
2020-01-30 11:50 ` Qian Cai
2020-01-30 12:35 ` Marco Elver
2020-01-31 2:18 ` Andrew Morton
2020-01-31 2:22 ` Qian Cai
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