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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 Subject: Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC Content-Language: en-US To: Uladzislau Rezki , Florian Westphal Cc: Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, Martin Zaharinov , Sebastian Andrzej Siewior References: <20220923103858.26729-1-fw@strlen.de> <20220923133512.GE22541@breakpoint.cc> <20220923145409.GF22541@breakpoint.cc> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1664204630; a=rsa-sha256; cv=none; b=TFDkkj6/hs1EKDhGDzKLe08sbkHOw4sXxTMxiWous1sOa5Sk2Re5XCRvlBe74mErJ1vdyZ qLop/BY+4kMnPBMAQpTCxrUwAwiDWusZC9mM4Es+PzuhyfapwsK/c4ZdPedVMStvpB5Ybf LoBuZDcrOgoj96iZL6P2hE1H4kbxTs0= ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=SA5M+y6N; 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dmarc=none; spf=pass (imf31.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Stat-Signature: k5m6j7txxowskogzr36zfgedyr75g59b X-Rspamd-Queue-Id: DF25A20012 X-HE-Tag: 1664204629-877634 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/23/22 17:10, Uladzislau Rezki wrote: > On Fri, Sep 23, 2022 at 04:54:09PM +0200, Florian Westphal wrote: >> Uladzislau Rezki wrote: >>> On Fri, Sep 23, 2022 at 03:35:12PM +0200, Florian Westphal wrote: >>>> Michal Hocko wrote: >>>>> On Fri 23-09-22 12:38:58, Florian Westphal wrote: >>>>>> Martin Zaharinov reports BUG() in mm land for 5.19.10 kernel: >>>>>> kernel BUG at mm/vmalloc.c:2437! >>>>>> invalid opcode: 0000 [#1] SMP >>>>>> CPU: 28 PID: 0 Comm: swapper/28 Tainted: G W O 5.19.9 #1 >>>>>> [..] >>>>>> RIP: 0010:__get_vm_area_node+0x120/0x130 >>>>>> __vmalloc_node_range+0x96/0x1e0 >>>>>> kvmalloc_node+0x92/0xb0 >>>>>> bucket_table_alloc.isra.0+0x47/0x140 >>>>>> rhashtable_try_insert+0x3a4/0x440 >>>>>> rhashtable_insert_slow+0x1b/0x30 >>>>>> [..] >>>>>> >>>>>> bucket_table_alloc uses kvzallocGPF_ATOMIC). If kmalloc fails, this now >>>>>> falls through to vmalloc and hits code paths that assume GFP_KERNEL. >>>>>> >>>>>> Revert the problematic change and stay with slab allocator. >>>>> >>>>> Why don't you simply fix the caller? >>>> >>>> Uh, not following? >>>> >>>> kvzalloc(GFP_ATOMIC) was perfectly fine, is this illegal again? >>>> >>> >>> static struct vm_struct *__get_vm_area_node(unsigned long size, >>> unsigned long align, unsigned long shift, unsigned long flags, >>> unsigned long start, unsigned long end, int node, >>> gfp_t gfp_mask, const void *caller) >>> { >>> struct vmap_area *va; >>> struct vm_struct *area; >>> unsigned long requested_size = size; >>> >>> BUG_ON(in_interrupt()); >>> ... >>> >>> >>> vmalloc is not supposed to be called from the IRQ context. >> >> It uses kvzalloc, not vmalloc api. >> >> Before 2018, rhashtable did use kzalloc OR kvzalloc, depending on gfp_t. >> >> Quote from 93f976b5190df327939 changelog: >> As of ce91f6ee5b3b ("mm: kvmalloc does not fallback to vmalloc for >> incompatible gfp flags") we can simplify the caller >> and trust kvzalloc() to just do the right thing. >> >> I fear that if this isn't allowed it will result in hard-to-spot bugs >> because things will work fine until a fallback to vmalloc happens. >> >> rhashtable may not be the only user of kvmalloc api that rely on >> ability to call it from (soft)irq. >> > Doing the "p = kmalloc(sizeof(*p), GFP_ATOMIC);" from an atomic context > is also a problem nowadays. Such code should be fixed across the kernel > because of PREEMPT_RT support. But the "atomic context" here is different, no? Calling kmalloc() from IRQ handlers AFAIK is ok as IRQ handlers are threaded on PREEMPT_RT. Calling it inside an local_irq_disable() would be a problem on the other hand. But then under e.g. spin_lock_irqsave() could be ok as those don't really disable irqs on RT. > -- > Uladzislau Rezki