Re: [PATCH v10 13/69] mm/mmap: use maple tree for unmapped_area{_topdown}

[Liam Howlett <liam.howlett@oracle.com>]

* Alexander Gordeev <agordeev@linux.ibm.com> [220709 03:29]:
> On Tue, Jun 21, 2022 at 08:46:55PM +0000, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
> > 
> > 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