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Date: Tue, 20 Sep 2022 11:20:33 +0300 From: Alexander Atanasov <alexander.atanasov@...tuozzo.com> To: Jonathan Corbet <corbet@....net>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, Roman Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com> Cc: kernel@...nvz.org, Alexander Atanasov <alexander.atanasov@...tuozzo.com>, Kees Cook <keescook@...omium.org>, Roman Gushchin <guro@...com>, Jann Horn <jannh@...gle.com>, Vijayanand Jitta <vjitta@...eaurora.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: [PATCH] mm: Make failslab writable again In (060807f841ac mm, slub: make remaining slub_debug related attributes read-only failslab) it was made RO. I think it became a collateral victim to the other two options (sanity_checks and trace) for which the reasons are perfectly valid. Here is why: - sanity_checks and trace are slab internal debug options, failslab is used for fault injection. - for fault injections, which by presumption are random, it does not matter if it is not set atomically. You need to set atleast one more option to trigger fault injection. - in a testing scenario you may need to change it at runtime example: module loading - you test all allocations limited by the space option. Then you move to test only your module's own slabs. - when set by command line flags it effectively disables all cache merges. Cc: Vlastimil Babka <vbabka@...e.cz> Cc: Andrew Morton <akpm@...ux-foundation.org> Cc: Kees Cook <keescook@...omium.org> Cc: Roman Gushchin <guro@...com> Cc: Christoph Lameter <cl@...ux.com> Cc: Jann Horn <jannh@...gle.com> Cc: Vijayanand Jitta <vjitta@...eaurora.org> Cc: David Rientjes <rientjes@...gle.com> Cc: Joonsoo Kim <iamjoonsoo.kim@....com> Cc: Pekka Enberg <penberg@...nel.org> Link: http://lkml.kernel.org/r/20200610163135.17364-5-vbabka@suse.cz Signed-off-by: Alexander Atanasov <alexander.atanasov@...tuozzo.com> --- Documentation/mm/slub.rst | 2 ++ mm/slub.c | 14 +++++++++++++- 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/Documentation/mm/slub.rst b/Documentation/mm/slub.rst index 43063ade737a..86837073a39e 100644 --- a/Documentation/mm/slub.rst +++ b/Documentation/mm/slub.rst @@ -116,6 +116,8 @@ options from the ``slub_debug`` parameter translate to the following files:: T trace A failslab +failslab file is writable, so writing 1 or 0 will enable or disable +the option at runtime. Write returns -EINVAL if cache is an alias. Careful with tracing: It may spew out lots of information and never stop if used on the wrong slab. diff --git a/mm/slub.c b/mm/slub.c index 862dbd9af4f5..7c15d312e0fb 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5617,7 +5617,19 @@ static ssize_t failslab_show(struct kmem_cache *s, char *buf) { return sysfs_emit(buf, "%d\n", !!(s->flags & SLAB_FAILSLAB)); } -SLAB_ATTR_RO(failslab); + +static ssize_t failslab_store(struct kmem_cache *s, const char *buf, + size_t length) +{ + if (s->refcount > 1) + return -EINVAL; + + s->flags &= ~SLAB_FAILSLAB; + if (buf[0] == '1') + s->flags |= SLAB_FAILSLAB; + return length; +} +SLAB_ATTR(failslab); #endif static ssize_t shrink_show(struct kmem_cache *s, char *buf) base-commit: 80e78fcce86de0288793a0ef0f6acf37656ee4cf -- 2.31.1
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