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[140.211.169.12]) by mx.google.com with ESMTPS id i39si9350864plb.210.2019.03.12.14.10.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Mar 2019 14:10:10 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id CCA49E3C; Tue, 12 Mar 2019 21:10:09 +0000 (UTC) Date: Tue, 12 Mar 2019 14:10:08 -0700 From: Andrew Morton To: Qian Cai Cc: catalin.marinas@arm.com, agraf@suse.de, paulus@ozlabs.org, benh@kernel.crashing.org, pe@ellerman.id.au, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] kmemleak: skip scanning holes in the .bss section Message-Id: <20190312141008.39eca5a0f03aaf2b86178ae9@linux-foundation.org> In-Reply-To: <20190312191412.28656-1-cai@lca.pw> References: <20190312191412.28656-1-cai@lca.pw> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Tue, 12 Mar 2019 15:14:12 -0400 Qian Cai wrote: > The commit 2d4f567103ff ("KVM: PPC: Introduce kvm_tmp framework") adds > kvm_tmp[] into the .bss section and then free the rest of unused spaces > back to the page allocator. > > kernel_init > kvm_guest_init > kvm_free_tmp > free_reserved_area > free_unref_page > free_unref_page_prepare > > With DEBUG_PAGEALLOC=y, it will unmap those pages from kernel. As the > result, kmemleak scan will trigger a panic below when it scans the .bss > section with unmapped pages. > > Since this is done way before the first kmemleak_scan(), just go > lockless to make the implementation simple and skip those pages when > scanning the .bss section. Later, those pages could be tracked by > kmemleak again once allocated by the page allocator. Overall, this is > such a special case, so no need to make it a generic to let kmemleak > gain an ability to skip blocks in scan_large_block(). > > BUG: Unable to handle kernel data access at 0xc000000001610000 > Faulting instruction address: 0xc0000000003cc178 > Oops: Kernel access of bad area, sig: 11 [#1] > LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=256 DEBUG_PAGEALLOC NUMA pSeries > CPU: 3 PID: 130 Comm: kmemleak Kdump: loaded Not tainted 5.0.0+ #9 > REGS: c0000004b05bf940 TRAP: 0300 Not tainted (5.0.0+) > NIP [c0000000003cc178] scan_block+0xa8/0x190 > LR [c0000000003cc170] scan_block+0xa0/0x190 > Call Trace: > [c0000004b05bfbd0] [c0000000003cc170] scan_block+0xa0/0x190 (unreliable) > [c0000004b05bfc30] [c0000000003cc2c0] scan_large_block+0x60/0xa0 > [c0000004b05bfc70] [c0000000003ccc64] kmemleak_scan+0x254/0x960 > [c0000004b05bfd40] [c0000000003cdd50] kmemleak_scan_thread+0xec/0x12c > [c0000004b05bfdb0] [c000000000104388] kthread+0x1b8/0x1c0 > [c0000004b05bfe20] [c00000000000b364] ret_from_kernel_thread+0x5c/0x78 > Instruction dump: > 7fa3eb78 4844667d 60000000 60000000 60000000 60000000 3bff0008 7fbcf840 > 409d00b8 4bfffeed 2fa30000 409e00ac e93e0128 7fa91840 > 419dffdc > hm, yes, this is super crude. I guess we can turn it into something more sophisticated if another caller is identified. > --- a/mm/kmemleak.c > +++ b/mm/kmemleak.c > @@ -237,6 +237,10 @@ static int kmemleak_skip_disable; > /* If there are leaks that can be reported */ > static bool kmemleak_found_leaks; > > +/* Skip scanning of a range in the .bss section. */ > +static void *bss_hole_start; > +static void *bss_hole_stop; > + > static bool kmemleak_verbose; > module_param_named(verbose, kmemleak_verbose, bool, 0600); > > @@ -1265,6 +1269,18 @@ void __ref kmemleak_ignore_phys(phys_addr_t phys) > } > EXPORT_SYMBOL(kmemleak_ignore_phys); > > +/** > + * kmemleak_bss_hole - skip scanning a range in the .bss section > + * > + * @start: start of the range > + * @stop: end of the range > + */ > +void kmemleak_bss_hole(void *start, void *stop) > +{ > + bss_hole_start = start; > + bss_hole_stop = stop; > +} I'll make this __init. > /* > * Update an object's checksum and return true if it was modified. > */ > @@ -1531,7 +1547,14 @@ static void kmemleak_scan(void) > > /* data/bss scanning */ > scan_large_block(_sdata, _edata); > - scan_large_block(__bss_start, __bss_stop); > + > + if (bss_hole_start) { > + scan_large_block(__bss_start, bss_hole_start); > + scan_large_block(bss_hole_stop, __bss_stop); > + } else { > + scan_large_block(__bss_start, __bss_stop); > + } > + > scan_large_block(__start_ro_after_init, __end_ro_after_init); > > #ifdef CONFIG_SMP