* Alexander Gordeev <agordeev@xxxxxxxxxxxxx> [220709 03:29]:
> On Tue, Jun 21, 2022 at 08:46:55PM +0000, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
> >
> > The maple tree code was added to find the unmapped area in a previous
> > commit and was checked against what the rbtree returned, but the actual
> > result was never used. Start using the maple tree implementation and
> > remove the rbtree code.
> >
> > Add kernel documentation comment for these functions.
>
> Hi Liam,
>
> With this update a user process crash is triggered on s390 when
> the below core is executed (derived from LTP fork14 testcase):
>
> #include <unistd.h>
> #include <sys/mman.h>
>
> #define GB (1024 * 1024 * 1024L)
> #define EXTENT (16 * 1024 + 10)
>
> int main(int argc, char **argv)
> {
> void *addr;
> int i;
>
> for (i = 0; i < EXTENT; i++) {
> addr = mmap(NULL, 1 * GB, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
> if (addr == MAP_FAILED)
> break;
> }
>
> return 0;
> }
>
> On 4095-th iteration mmap() returns a normal address, but shared
> library mappings go away. The page tables seem to be intact as the
> memory is still available (I did not check every mapping gone though).
> In addition, the memory contents of disappeared mappings is zeroed.
> As result, an instruction that follows the mmap() system call turns
> into invalid operation code:
>
> t35lp64 login: [45116.631391] User process fault: interruption code 0004 ilc:1
> [45116.631403] Failing address: 000003ffa580c000 TEID: 000003ffa580c884
> [45116.631405] Fault in primary space mode while using user ASCE.
> [45116.631407] AS:00000000e75fc1c7 R3:00000000e758c007 S:00000000a3e01701
> [45116.631411] CPU: 4 PID: 1745 Comm: mmap Not tainted 5.19.0-rc4-00162-g34de4ebd5706 #36
> [45116.631414] Hardware name: IBM 8561 T01 703 (LPAR)
> [45116.631416] User PSW : 0705000180000000 000003ffa580cc38
> [45116.631418] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:1 AS:0 CC:0 PM:0 RI:0 EA:3
> [45116.631420] User GPRS: 0000000000000000 000003ffa5af4040 000003ff65afb000 0000000040000000
> [45116.631422] 0000000000000003 0000000000000022 0000000000000000 0000000001003e00
> [45116.631423] 000003ffa5ab0b48 000003ffa5ab1018 0000000000000001 000003fff5879500
> [45116.631425] 000003ffa5ab0f70 0000000000000000 0000000001001218 000003fff5879428
> [45116.631429] User Code: 000003ffa580cc32: 0000 illegal
> [45116.631429] 000003ffa580cc34: 0000 illegal
> [45116.631429] #000003ffa580cc36: 0000 illegal
> [45116.631429] >000003ffa580cc38: 0000 illegal
> [45116.631429] 000003ffa580cc3a: 0000 illegal
> [45116.631429] 000003ffa580cc3c: 0000 illegal
> [45116.631429] 000003ffa580cc3e: 0000 illegal
> [45116.631429] 000003ffa580cc40: 0000 illegal
> [45116.631437] Last Breaking-Event-Address:
> [45116.631438] [<0000000000000001>] 0x1
>
> In other words, if before the mmap() call memory mappings look like this:
>
> Start Addr End Addr Size Offset Perms objfile
> 0x1000000 0x1001000 0x1000 0x0 r--p /root/main/mmap
> 0x1001000 0x1002000 0x1000 0x1000 r-xp /root/main/mmap
> 0x1002000 0x1003000 0x1000 0x2000 r--p /root/main/mmap
> 0x1003000 0x1004000 0x1000 0x2000 r--p /root/main/mmap
> 0x1004000 0x1005000 0x1000 0x3000 rw-p /root/main/mmap
> 0x3fff7c00000 0x3fff7c2b000 0x2b000 0x0 r--p /usr/lib64/libc.so.6
> 0x3fff7c2b000 0x3fff7d64000 0x139000 0x2b000 r-xp /usr/lib64/libc.so.6
> 0x3fff7d64000 0x3fff7dc3000 0x5f000 0x164000 r--p /usr/lib64/libc.so.6
> 0x3fff7dc3000 0x3fff7dc4000 0x1000 0x1c3000 ---p /usr/lib64/libc.so.6
> 0x3fff7dc4000 0x3fff7dc8000 0x4000 0x1c3000 r--p /usr/lib64/libc.so.6
> 0x3fff7dc8000 0x3fff7dca000 0x2000 0x1c7000 rw-p /usr/lib64/libc.so.6
> 0x3fff7dca000 0x3fff7dd2000 0x8000 0x0 rw-p
> 0x3fff7f80000 0x3fff7f82000 0x2000 0x0 r--p /usr/lib/ld64.so.1
> 0x3fff7f82000 0x3fff7fa3000 0x21000 0x2000 r-xp /usr/lib/ld64.so.1
> 0x3fff7fa3000 0x3fff7faf000 0xc000 0x23000 r--p /usr/lib/ld64.so.1
> 0x3fff7faf000 0x3fff7fb1000 0x2000 0x2e000 r--p /usr/lib/ld64.so.1
> 0x3fff7fb1000 0x3fff7fb3000 0x2000 0x30000 rw-p /usr/lib/ld64.so.1
> 0x3fff7ff3000 0x3fff7ffb000 0x8000 0x0 rw-p
> 0x3fffffda000 0x3ffffffb000 0x21000 0x0 rw-p [stack]
> 0x3ffffffc000 0x3ffffffe000 0x2000 0x0 r--p [vvar]
> 0x3ffffffe000 0x40000000000 0x2000 0x0 r-xp [vdso]
>
> Then after mmap() returns it turns into:
>
> Start Addr End Addr Size Offset Perms objfile
> 0x1000000 0x1001000 0x1000 0x0 r--p /root/main/mmap
> 0x1001000 0x1002000 0x1000 0x1000 r-xp /root/main/mmap
> 0x1002000 0x1003000 0x1000 0x2000 r--p /root/main/mmap
> 0x1003000 0x1004000 0x1000 0x2000 r--p /root/main/mmap
> 0x1004000 0x1005000 0x1000 0x3000 rw-p /root/main/mmap
> 0x37c00000 0x3fff7ffb000 0x3ffc03fb000 0x0 rw-p
> 0x3fffffda000 0x3ffffffb000 0x21000 0x0 rw-p [stack]
> 0x3ffffffc000 0x3ffffffe000 0x2000 0x0 r--p [vvar]
> 0x3ffffffe000 0x40000000000 0x2000 0x0 r-xp [vdso]
>
> Interestingly, all addresses mmap() returns before the problem hits are
> 1MB-aligned, while the last one that screws the mappings is always page-
> aligned. Also, the iteration number 4095 suggests some arithmetics that
> leads to an integer overflow.
>
> I did not experiment much with x86, but the problem does not hit there.
> The config has CONFIG_PGTABLE_LEVELS=5, but I am not sure about other
> options that may be involved.
>
> The tree I used to isolate the issue:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm mm-everything
>
> It (looks like it) gets pulled into every linux-next, so the problem
> is reproducable there as well.
>
> As we are approaching the merge window that looks pretty worrisome. I will
> try to get more details on what is going on, but may be you have an immediate
> idea?
Thank you for testing this code. Yes, it is because I was not returning
the error code which I had set when gap searching was exhausted. What
is happening is that, because I had not returned the error, the mmap
code will munmap the area and replace it with your requested map. There
will be a patch for the maple tree in your inbox shortly.
Regards,
Liam
