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(p200300cbc70e2600cd607701f644b131.dip0.t-ipconnect.de. [2003:cb:c70e:2600:cd60:7701:f644:b131]) by smtp.gmail.com with ESMTPSA id q2-20020a5d5742000000b0033cf60e268fsm14070wrw.116.2024.03.13.14.03.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 13 Mar 2024 14:03:50 -0700 (PDT) Message-ID: <2b794ff8-7805-44d5-9a4e-0870e270365f@redhat.com> Date: Wed, 13 Mar 2024 22:03:48 +0100 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 06/24] fsverity: pass tree_blocksize to end_enable_verity() Content-Language: en-US From: David Hildenbrand To: "Darrick J. Wong" Cc: Matthew Wilcox , Andrey Albershteyn , fsverity@lists.linux.dev, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, chandan.babu@oracle.com, akpm@linux-foundation.org, linux-mm@kvack.org, Eric Biggers References: <20240305005242.GE17145@sol.localdomain> <20240306163000.GP1927156@frogsfrogsfrogs> <20240307220224.GA1799@sol.localdomain> <20240308034650.GK1927156@frogsfrogsfrogs> <20240308044017.GC8111@sol.localdomain> <20240311223815.GW1927156@frogsfrogsfrogs> <9927568e-9f36-4417-9d26-c8a05c220399@redhat.com> <08905bcc-677d-4981-926d-7f407b2f6a4a@redhat.com> <20240312164444.GG1927156@frogsfrogsfrogs> <420b6d5f-adef-4415-b8cb-16c234dcec38@redhat.com> <20240313171936.GN1927156@frogsfrogsfrogs> Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 13.03.24 20:10, David Hildenbrand wrote: > On 13.03.24 18:19, Darrick J. Wong wrote: >> On Wed, Mar 13, 2024 at 01:29:12PM +0100, David Hildenbrand wrote: >>> On 12.03.24 17:44, Darrick J. Wong wrote: >>>> On Tue, Mar 12, 2024 at 04:33:14PM +0100, David Hildenbrand wrote: >>>>> On 12.03.24 16:13, David Hildenbrand wrote: >>>>>> On 11.03.24 23:38, Darrick J. Wong wrote: >>>>>>> [add willy and linux-mm] >>>>>>> >>>>>>> On Thu, Mar 07, 2024 at 08:40:17PM -0800, Eric Biggers wrote: >>>>>>>> On Thu, Mar 07, 2024 at 07:46:50PM -0800, Darrick J. Wong wrote: >>>>>>>>>> BTW, is xfs_repair planned to do anything about any such extra blocks? >>>>>>>>> >>>>>>>>> Sorry to answer your question with a question, but how much checking is >>>>>>>>> $filesystem expected to do for merkle trees? >>>>>>>>> >>>>>>>>> In theory xfs_repair could learn how to interpret the verity descriptor, >>>>>>>>> walk the merkle tree blocks, and even read the file data to confirm >>>>>>>>> intactness. If the descriptor specifies the highest block address then >>>>>>>>> we could certainly trim off excess blocks. But I don't know how much of >>>>>>>>> libfsverity actually lets you do that; I haven't looked into that >>>>>>>>> deeply. :/ >>>>>>>>> >>>>>>>>> For xfs_scrub I guess the job is theoretically simpler, since we only >>>>>>>>> need to stream reads of the verity files through the page cache and let >>>>>>>>> verity tell us if the file data are consistent. >>>>>>>>> >>>>>>>>> For both tools, if something finds errors in the merkle tree structure >>>>>>>>> itself, do we turn off verity? Or do we do something nasty like >>>>>>>>> truncate the file? >>>>>>>> >>>>>>>> As far as I know (I haven't been following btrfs-progs, but I'm familiar with >>>>>>>> e2fsprogs and f2fs-tools), there isn't yet any precedent for fsck actually >>>>>>>> validating the data of verity inodes against their Merkle trees. >>>>>>>> >>>>>>>> e2fsck does delete the verity metadata of inodes that don't have the verity flag >>>>>>>> enabled. That handles cleaning up after a crash during FS_IOC_ENABLE_VERITY. >>>>>>>> >>>>>>>> I suppose that ideally, if an inode's verity metadata is invalid, then fsck >>>>>>>> should delete that inode's verity metadata and remove the verity flag from the >>>>>>>> inode. Checking for a missing or obviously corrupt fsverity_descriptor would be >>>>>>>> fairly straightforward, but it probably wouldn't catch much compared to actually >>>>>>>> validating the data against the Merkle tree. And actually validating the data >>>>>>>> against the Merkle tree would be complex and expensive. Note, none of this >>>>>>>> would work on files that are encrypted. >>>>>>>> >>>>>>>> Re: libfsverity, I think it would be possible to validate a Merkle tree using >>>>>>>> libfsverity_compute_digest() and the callbacks that it supports. But that's not >>>>>>>> quite what it was designed for. >>>>>>>> >>>>>>>>> Is there an ioctl or something that allows userspace to validate an >>>>>>>>> entire file's contents? Sort of like what BLKVERIFY would have done for >>>>>>>>> block devices, except that we might believe its answers? >>>>>>>> >>>>>>>> Just reading the whole file and seeing whether you get an error would do it. >>>>>>>> >>>>>>>> Though if you want to make sure it's really re-reading the on-disk data, it's >>>>>>>> necessary to drop the file's pagecache first. >>>>>>> >>>>>>> I tried a straight pagecache read and it worked like a charm! >>>>>>> >>>>>>> But then I thought to myself, do I really want to waste memory bandwidth >>>>>>> copying a bunch of data? No. I don't even want to incur system call >>>>>>> overhead from reading a single byte every $pagesize bytes. >>>>>>> >>>>>>> So I created 2M mmap areas and read a byte every $pagesize bytes. That >>>>>>> worked too, insofar as SIGBUSes are annoying to handle. But it's >>>>>>> annoying to take signals like that. >>>>>>> >>>>>>> Then I started looking at madvise. MADV_POPULATE_READ looked exactly >>>>>>> like what I wanted -- it prefaults in the pages, and "If populating >>>>>>> fails, a SIGBUS signal is not generated; instead, an error is returned." >>>>>>> >>>>>> >>>>>> Yes, these were the expected semantics :) >>>>>> >>>>>>> But then I tried rigging up a test to see if I could catch an EIO, and >>>>>>> instead I had to SIGKILL the process! It looks filemap_fault returns >>>>>>> VM_FAULT_RETRY to __xfs_filemap_fault, which propagates up through >>>>>>> __do_fault -> do_read_fault -> do_fault -> handle_pte_fault -> >>>>>>> handle_mm_fault -> faultin_page -> __get_user_pages. At faultin_pages, >>>>>>> the VM_FAULT_RETRY is translated to -EBUSY. >>>>>>> >>>>>>> __get_user_pages squashes -EBUSY to 0, so faultin_vma_page_range returns >>>>>>> that to madvise_populate. Unfortunately, madvise_populate increments >>>>>>> its loop counter by the return value (still 0) so it runs in an >>>>>>> infinite loop. The only way out is SIGKILL. >>>>>> >>>>>> That's certainly unexpected. One user I know is QEMU, which primarily >>>>>> uses MADV_POPULATE_WRITE to prefault page tables. Prefaulting in QEMU is >>>>>> primarily used with shmem/hugetlb, where I haven't heard of any such >>>>>> endless loops. >>>>>> >>>>>>> >>>>>>> So I don't know what the correct behavior is here, other than the >>>>>>> infinite loop seems pretty suspect. Is it the correct behavior that >>>>>>> madvise_populate returns EIO if __get_user_pages ever returns zero? >>>>>>> That doesn't quite sound right if it's the case that a zero return could >>>>>>> also happen if memory is tight. >>>>>> >>>>>> madvise_populate() ends up calling faultin_vma_page_range() in a loop. >>>>>> That one calls __get_user_pages(). >>>>>> >>>>>> __get_user_pages() documents: "0 return value is possible when the fault >>>>>> would need to be retried." >>>>>> >>>>>> So that's what the caller does. IIRC, there are cases where we really >>>>>> have to retry (at least once) and will make progress, so treating "0" as >>>>>> an error would be wrong. >>>>>> >>>>>> Staring at other __get_user_pages() users, __get_user_pages_locked() >>>>>> documents: "Please note that this function, unlike __get_user_pages(), >>>>>> will not return 0 for nr_pages > 0, unless FOLL_NOWAIT is used.". >>>>>> >>>>>> But there is some elaborate retry logic in there, whereby the retry will >>>>>> set FOLL_TRIED->FAULT_FLAG_TRIED, and I think we'd fail on the second >>>>>> retry attempt (there are cases where we retry more often, but that's >>>>>> related to something else I believe). >>>>>> >>>>>> So maybe we need a similar retry logic in faultin_vma_page_range()? Or >>>>>> make it use __get_user_pages_locked(), but I recall when I introduced >>>>>> MADV_POPULATE_READ, there was a catch to it. >>>>> >>>>> I'm trying to figure out who will be setting the VM_FAULT_SIGBUS in the >>>>> mmap()+access case you describe above. >>>>> >>>>> Staring at arch/x86/mm/fault.c:do_user_addr_fault(), I don't immediately see >>>>> how we would transition from a VM_FAULT_RETRY loop to VM_FAULT_SIGBUS. >>>>> Because VM_FAULT_SIGBUS would be required for that function to call >>>>> do_sigbus(). >>>> >>>> The code I was looking at yesterday in filemap_fault was: >>>> >>>> page_not_uptodate: >>>> /* >>>> * Umm, take care of errors if the page isn't up-to-date. >>>> * Try to re-read it _once_. We do this synchronously, >>>> * because there really aren't any performance issues here >>>> * and we need to check for errors. >>>> */ >>>> fpin = maybe_unlock_mmap_for_io(vmf, fpin); >>>> error = filemap_read_folio(file, mapping->a_ops->read_folio, folio); >>>> if (fpin) >>>> goto out_retry; >>>> folio_put(folio); >>>> >>>> if (!error || error == AOP_TRUNCATED_PAGE) >>>> goto retry_find; >>>> filemap_invalidate_unlock_shared(mapping); >>>> >>>> return VM_FAULT_SIGBUS; >>>> >>>> Wherein I /think/ fpin is non-null in this case, so if >>>> filemap_read_folio returns an error, we'll do this instead: >>>> >>>> out_retry: >>>> /* >>>> * We dropped the mmap_lock, we need to return to the fault handler to >>>> * re-find the vma and come back and find our hopefully still populated >>>> * page. >>>> */ >>>> if (!IS_ERR(folio)) >>>> folio_put(folio); >>>> if (mapping_locked) >>>> filemap_invalidate_unlock_shared(mapping); >>>> if (fpin) >>>> fput(fpin); >>>> return ret | VM_FAULT_RETRY; >>>> >>>> and since ret was 0 before the goto, the only return code is >>>> VM_FAULT_RETRY. I had speculated that perhaps we could instead do: >>>> >>>> if (fpin) { >>>> if (error) >>>> ret |= VM_FAULT_SIGBUS; >>>> goto out_retry; >>>> } >>>> >>>> But I think the hard part here is that there doesn't seem to be any >>>> distinction between transient read errors (e.g. disk cable fell out) vs. >>>> semi-permanent errors (e.g. verity says the hash doesn't match). >>>> AFAICT, either the read(ahead) sets uptodate and callers read the page, >>>> or it doesn't set it and callers treat that as an error-retry >>>> opportunity. >>>> >>>> For the transient error case VM_FAULT_RETRY makes perfect sense; for the >>>> second case I imagine we'd want something closer to _SIGBUS. >>> >>> >>> Agreed, it's really hard to judge when it's the right time to give up >>> retrying. At least with MADV_POPULATE_READ we should try achieving the same >>> behavior as with mmap()+read access. So if the latter manages to trigger >>> SIGBUS, MADV_POPULATE_READ should return an error. >>> >>> Is there an easy way to for me to reproduce this scenario? >> >> Yes. Take this Makefile: >> >> CFLAGS=-Wall -Werror -O2 -g -Wno-unused-variable >> >> all: mpr >> >> and this C program mpr.c: >> >> /* test MAP_POPULATE_READ on a file */ >> #include >> #include >> #include >> #include >> #include >> #include >> #include >> >> #define min(a, b) ((a) < (b) ? (a) : (b)) >> #define BUFSIZE (2097152) >> >> int main(int argc, char *argv[]) >> { >> struct stat sb; >> long pagesize = sysconf(_SC_PAGESIZE); >> off_t read_sz, pos; >> void *addr; >> char c; >> int fd, ret; >> >> if (argc != 2) { >> printf("Usage: %s fname\n", argv[0]); >> return 1; >> } >> >> fd = open(argv[1], O_RDONLY); >> if (fd < 0) { >> perror(argv[1]); >> return 1; >> } >> >> ret = fstat(fd, &sb); >> if (ret) { >> perror("fstat"); >> return 1; >> } >> >> /* Validate the file contents with regular reads */ >> for (pos = 0; pos < sb.st_size; pos += sb.st_blksize) { >> ret = pread(fd, &c, 1, pos); >> if (ret < 0) { >> if (errno != EIO) { >> perror("pread"); >> return 1; >> } >> >> printf("%s: at offset %llu: %s\n", argv[1], >> (unsigned long long)pos, >> strerror(errno)); >> break; >> } >> } >> >> ret = pread(fd, &c, 1, sb.st_size); >> if (ret < 0) { >> if (errno != EIO) { >> perror("pread"); >> return 1; >> } >> >> printf("%s: at offset %llu: %s\n", argv[1], >> (unsigned long long)sb.st_size, >> strerror(errno)); >> } >> >> /* Validate the file contents with MADV_POPULATE_READ */ >> read_sz = ((sb.st_size + (pagesize - 1)) / pagesize) * pagesize; >> printf("%s: read bytes %llu\n", argv[1], (unsigned long long)read_sz); >> >> for (pos = 0; pos < read_sz; pos += BUFSIZE) { >> unsigned int mappos; >> size_t maplen = min(read_sz - pos, BUFSIZE); >> >> addr = mmap(NULL, maplen, PROT_READ, MAP_SHARED, fd, pos); >> if (addr == MAP_FAILED) { >> perror("mmap"); >> return 1; >> } >> >> ret = madvise(addr, maplen, MADV_POPULATE_READ); >> if (ret) { >> perror("madvise"); >> return 1; >> } >> >> ret = munmap(addr, maplen); >> if (ret) { >> perror("munmap"); >> return 1; >> } >> } >> >> ret = close(fd); >> if (ret) { >> perror("close"); >> return 1; >> } >> >> return 0; >> } >> >> and this shell script mpr.sh: >> >> #!/bin/bash -x >> >> # Try to trigger infinite loop with regular IO errors and MADV_POPULATE_READ >> >> scriptdir="$(dirname "$0")" >> >> commands=(dmsetup mkfs.xfs xfs_io timeout strace "$scriptdir/mpr") >> for cmd in "${commands[@]}"; do >> if ! command -v "$cmd" &>/dev/null; then >> echo "$cmd: Command required for this program." >> exit 1 >> fi >> done >> >> dev="${1:-/dev/sda}" >> mnt="${2:-/mnt}" >> dmtarget="dumbtarget" >> >> # Clean up any old mounts >> umount "$dev" "$mnt" >> dmsetup remove "$dmtarget" >> rmmod xfs >> >> # Create dm linear mapping to block device and format filesystem >> sectors="$(blockdev --getsz "$dev")" >> tgt="/dev/mapper/$dmtarget" >> echo "0 $sectors linear $dev 0" | dmsetup create "$dmtarget" >> mkfs.xfs -f "$tgt" >> >> # Create a file that we'll read, then cycle mount to zap pagecache >> mount "$tgt" "$mnt" >> xfs_io -f -c "pwrite -S 0x58 0 1m" "$mnt/a" >> umount "$mnt" >> mount "$tgt" "$mnt" >> >> # Load file metadata >> stat "$mnt/a" >> >> # Induce EIO errors on read >> dmsetup suspend --noflush --nolockfs "$dmtarget" >> echo "0 $sectors error" | dmsetup load "$dmtarget" >> dmsetup resume "$dmtarget" >> >> # Try to provoke the kernel; kill the process after 10s so we can clean up >> timeout -s KILL 10s strace -s99 -e madvise "$scriptdir/mpr" "$mnt/a" >> >> # Stop EIO errors so we can unmount >> dmsetup suspend --noflush --nolockfs "$dmtarget" >> echo "0 $sectors linear $dev 0" | dmsetup load "$dmtarget" >> dmsetup resume "$dmtarget" >> >> # Unmount and clean up after ourselves >> umount "$mnt" >> dmsetup remove "$dmtarget" >> >> >> make the C program, then run ./mpr.sh . It should >> stall in the madvise call until timeout sends sigkill to the program; >> you can crank the 10s timeout up if you want. >> >> > > Yes, seems to work, nice! > > > [ 452.455636] buffer_io_error: 6 callbacks suppressed > [ 452.455638] Buffer I/O error on dev dm-0, logical block 16, async page read > [ 452.456169] Buffer I/O error on dev dm-0, logical block 17, async page read > [ 452.456456] Buffer I/O error on dev dm-0, logical block 18, async page read > [ 452.456754] Buffer I/O error on dev dm-0, logical block 19, async page read > [ 452.457061] Buffer I/O error on dev dm-0, logical block 20, async page read > [ 452.457350] Buffer I/O error on dev dm-0, logical block 21, async page read > [ 452.457639] Buffer I/O error on dev dm-0, logical block 22, async page read > [ 452.457942] Buffer I/O error on dev dm-0, logical block 23, async page read > [ 452.458242] Buffer I/O error on dev dm-0, logical block 16, async page read > [ 452.458552] Buffer I/O error on dev dm-0, logical block 17, async page read > + timeout -s KILL 10s strace -s99 -e madvise ./mpr /mnt/tmp//a > /mnt/tmp//a: at offset 0: Input/output error > /mnt/tmp//a: read bytes 1048576 > madvise(0x7f9393624000, 1048576, MADV_POPULATE_READ./mpr.sh: line 45: 2070 Killed tim" > > > And once I switch over to reading instead of MADV_POPULATE_READ: > > [ 753.940230] buffer_io_error: 6 callbacks suppressed > [ 753.940233] Buffer I/O error on dev dm-0, logical block 8192, async page read > [ 753.941402] Buffer I/O error on dev dm-0, logical block 8193, async page read > [ 753.942084] Buffer I/O error on dev dm-0, logical block 8194, async page read > [ 753.942738] Buffer I/O error on dev dm-0, logical block 8195, async page read > [ 753.943412] Buffer I/O error on dev dm-0, logical block 8196, async page read > [ 753.944088] Buffer I/O error on dev dm-0, logical block 8197, async page read > [ 753.944741] Buffer I/O error on dev dm-0, logical block 8198, async page read > [ 753.945415] Buffer I/O error on dev dm-0, logical block 8199, async page read > [ 753.946105] Buffer I/O error on dev dm-0, logical block 8192, async page read > [ 753.946661] Buffer I/O error on dev dm-0, logical block 8193, async page read > + timeout -s KILL 10s strace -s99 -e madvise ./mpr /mnt/tmp//a > /mnt/tmp//a: at offset 0: Input/output error > /mnt/tmp//a: read bytes 1048576 > --- SIGBUS {si_signo=SIGBUS, si_code=BUS_ADRERR, si_addr=0x7f34f82d8000} --- > +++ killed by SIGBUS (core dumped) +++ > timeout: the monitored command dumped core > ./mpr.sh: line 45: 2388 Bus error timeout -s KILL 10s strace -s99 -e madvise "$scriptdir" > > > Let me dig how the fault handler is able to conclude SIGBUS here! Might be as simple as this: diff --git a/mm/gup.c b/mm/gup.c index df83182ec72d5..62df1548b7779 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1734,8 +1734,8 @@ long faultin_vma_page_range(struct vm_area_struct *vma, unsigned long start, if (check_vma_flags(vma, gup_flags)) return -EINVAL; - ret = __get_user_pages(mm, start, nr_pages, gup_flags, - NULL, locked); + ret = __get_user_pages_locked(mm, start, nr_pages, NULL, locked, + gup_flags); lru_add_drain(); return ret; } [ 57.154542] Buffer I/O error on dev dm-0, logical block 16, async page read [ 57.155276] Buffer I/O error on dev dm-0, logical block 17, async page read [ 57.155911] Buffer I/O error on dev dm-0, logical block 18, async page read [ 57.156568] Buffer I/O error on dev dm-0, logical block 19, async page read [ 57.157245] Buffer I/O error on dev dm-0, logical block 20, async page read [ 57.157880] Buffer I/O error on dev dm-0, logical block 21, async page read [ 57.158539] Buffer I/O error on dev dm-0, logical block 22, async page read [ 57.159197] Buffer I/O error on dev dm-0, logical block 23, async page read [ 57.159838] Buffer I/O error on dev dm-0, logical block 16, async page read [ 57.160492] Buffer I/O error on dev dm-0, logical block 17, async page read + timeout -s KILL 10s strace -s99 -e madvise ./mpr /mnt/tmp//a [ 57.190472] Retrying /mnt/tmp//a: at offset 0: Input/output error /mnt/tmp//a: read bytes 1048576 madvise(0x7f0fa0384000, 1048576, MADV_POPULATE_READ) = -1 EFAULT (Bad address) madvise: Bad address And -EFAULT is what MADV_POPULATE_READ is documented to return for SIGBUS. (there are a couple of ways we could speedup MADV_POPULATE_READ, maybe at some point using VMA locks) -- Cheers, David / dhildenb