From: David Howells <[EMAIL PROTECTED]>
Make the SYSV SHM nattch counter work correctly by forcing multiple VMAs to be
produced to represent MAP_SHARED segments, even if they overlap exactly.
Using this test program:
http://people.redhat.com/~dhowells/doshm.c
Run as:
doshm sysv
I can see nattch going from one before the patch:
# /doshm sysv
Command: sysv
shmid: 65536
memory: 0xc3700000
c0b00000-c0b04000 rw-p 00000000 00:00 0
c0bb0000-c0bba788 r-xs 00000000 00:0b 14582157 /lib/ld-uClibc-0.9.28.so
c3180000-c31dede4 r-xs 00000000 00:0b 14582179 /lib/libuClibc-0.9.28.so
c3520000-c352278c rw-p 00000000 00:0b 13763417 /doshm
c3584000-c35865e8 r-xs 00000000 00:0b 13763417 /doshm
c3588000-c358aa00 rw-p 00008000 00:0b 14582157 /lib/ld-uClibc-0.9.28.so
c3590000-c359b6c0 rw-p 00000000 00:00 0
c3620000-c3640000 rwxp 00000000 00:00 0
c3700000-c37fa000 rw-S 00000000 00:06 1411 /SYSV00000000 (deleted)
c3700000-c37fa000 rw-S 00000000 00:06 1411 /SYSV00000000 (deleted)
nattch 1
To two after the patch:
# /doshm sysv
Command: sysv
shmid: 0
memory: 0xc3700000
c0bb0000-c0bba788 r-xs 00000000 00:0b 14582157 /lib/ld-uClibc-0.9.28.so
c3180000-c31dede4 r-xs 00000000 00:0b 14582179 /lib/libuClibc-0.9.28.so
c3320000-c3340000 rwxp 00000000 00:00 0
c3530000-c35325e8 r-xs 00000000 00:0b 13763417 /doshm
c3534000-c353678c rw-p 00000000 00:0b 13763417 /doshm
c3538000-c353aa00 rw-p 00008000 00:0b 14582157 /lib/ld-uClibc-0.9.28.so
c3590000-c359b6c0 rw-p 00000000 00:00 0
c35a4000-c35a8000 rw-p 00000000 00:00 0
c3700000-c37fa000 rw-S 00000000 00:06 1369 /SYSV00000000 (deleted)
c3700000-c37fa000 rw-S 00000000 00:06 1369 /SYSV00000000 (deleted)
nattch 2
That's +1 to nattch for each shmat() made.
Signed-Off-By: David Howells <[EMAIL PROTECTED]>
---
mm/nommu.c | 6 ++++++
1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/mm/nommu.c b/mm/nommu.c
index ba6df4d..cbbc137 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -826,6 +826,11 @@ unsigned long do_mmap_pgoff(struct file *file,
unsigned long pglen = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
unsigned long vmpglen;
+ /* suppress VMA sharing for shared regions */
+ if (vm_flags & VM_SHARED &&
+ capabilities & BDI_CAP_MAP_DIRECT)
+ goto dont_share_VMAs;
+
for (rb = rb_first(&nommu_vma_tree); rb; rb = rb_next(rb)) {
vma = rb_entry(rb, struct vm_area_struct, vm_rb);
@@ -859,6 +864,7 @@ unsigned long do_mmap_pgoff(struct file *file,
goto shared;
}
+ dont_share_VMAs:
vma = NULL;
/* obtain the address at which to make a shared mapping
-
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