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Improve mmap MAP_HUGETLB support.

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This is a follow up to r14682:

When an mmap retry is done without any constraints, the kernel can
place it into free or reservation segments (i.e. anywhere there is no
mapping yet).
In r14682 a sanity check made the hypothesis that the new mapping was
in a free segment, but it does not hold at least on Linux 3.12 and 3.16
on amd64 (tested under Debian).
There is no risk in allowing the mapping to end up in (what was
previously) a reservation at this point, because it is also allowed.

Patch by Guillaume Knispel <xilun0@gmail.com>. Fixes BZ #348269.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15538
This commit is contained in:
Florian Krohm 2015-08-13 20:35:03 +00:00
parent a2df7642ef
commit cdf7f871da
3 changed files with 15 additions and 6 deletions
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1
NEWS
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@ -267,6 +267,7 @@ where XXXXXX is the bug number as listed below.
== 345929
348102 Patch updating v4l2 API support
348247 jno jumps wrongly when overflow is not set
348269 Improve mmap MAP_HUGETLB support.
348565 Fix detection of command line option availability for clang
348728 Fix broken check for VIDIOC_G_ENC_INDEX
348748 Fix redundant condition

18
coregrind/m_syswrap/syswrap-generic.c
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@ -2323,9 +2323,9 @@ ML_(generic_PRE_sys_mmap) ( ThreadId tid,
to understand special file system mount options).
So, let's just redo an mmap, without giving any constraint to
the kernel. If that succeeds, check with aspacem that the returned
address is acceptable (i.e. is free).
address is acceptable.
This will give a similar effect as if the user would have
specified a MAP_FIXED at that address.
hinted that address.
The aspacem state will be correctly updated afterwards.
We however cannot do this last refinement when the user asked
for a fixed mapping, as the user asked a specific address. */
@ -2337,8 +2337,18 @@ ML_(generic_PRE_sys_mmap) ( ThreadId tid,
arg4,
arg5, arg6);
if (!sr_isError(sres)) {
vg_assert(VG_(am_covered_by_single_free_segment)((Addr)sr_Res(sres),
arg2));
/* The kernel is supposed to know what it is doing, but let's
do a last sanity check anyway, as if the chosen address had
been initially hinted by the client. The whole point of this
last try was to allow mmap of huge pages to succeed without
making aspacem understand them, on the other hand the kernel
does not know about valgrind reservations, so this mapping
can end up in free space and reservations. */
mreq.start = (Addr)sr_Res(sres);
mreq.len = arg2;
mreq.rkind = MHint;
advised = VG_(am_get_advisory)( &mreq, True/*client*/, &mreq_ok );
vg_assert(mreq_ok && advised == mreq.start);
}
}

2
docs/internals/3_10_BUGSTATUS.txt
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@ -144,8 +144,6 @@ go in here.
345414 WARNING: unhandled syscall: 317 (sys_seccomp)
348269 support of mmap for huge pages is broken at least on amd64
348616 Wine/valgrind: Warning: noted but unhandled ioctl 0x5390 with
no size/direction hints. (DVD_READ_STRUCT)