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types: member m_fd in BeesFileRange must be protected against data races

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We had an unfortunate pattern of:

	const BeesFileRange bfr;
	shared_ptr<BeesContext> ctx;
	// ...
	BEESNOTE("foo " << bfr);
	bfr.fd(ctx);
	BEESNOTE("foo after opening: " << bfr);

If dump_status started running after the first BEESNOTE, but before
the second, then bfr.fd() might expose a single Fd object's shared_ptr
member to two threads at the same time (the thread running dump_status
and the thread running BEESNOTE) without protection by a lock.  One of
the threads would see a partially-initialized Fd object, and the other
thread would crash on an assertion failure, e.g.

	#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
	#1  0x00007f4c4fde5537 in __GI_abort () at abort.c:79
	#2  0x00007f4c4fde540f in __assert_fail_base (fmt=0x7f4c4ff4e128 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=0x5557605629dd "!m_destroyed", file=0x5557605627c0 "../include/crucible/namedptr.h", line=77, function=<optimized out>) at assert.c:92
	#3  0x00007f4c4fdf4662 in __GI___assert_fail (assertion=assertion@entry=0x5557605629dd "!m_destroyed", file=file@entry=0x5557605627c0 "../include/crucible/namedptr.h", line=line@entry=77,
	    function=function@entry=0x555760562970 "crucible::NamedPtr<Return, Arguments>::Value::~Value() [with Return = crucible::IOHandle; Arguments = {int}]") at assert.c:101
	#4  0x00005557605306f6 in crucible::NamedPtr<crucible::IOHandle, int>::Value::~Value (this=0x7f4a3c2ff0d0, __in_chrg=<optimized out>) at ../include/crucible/namedptr.h:77
	#5  0x00005557605137da in std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7f4a3c2ff0c0) at /usr/include/c++/10/bits/shared_ptr_base.h:151
	#6  std::_Sp_counted_base<(__gnu_cxx::_Lock_policy)2>::_M_release (this=0x7f4a3c2ff0c0) at /usr/include/c++/10/bits/shared_ptr_base.h:151
	#7  std::__shared_count<(__gnu_cxx::_Lock_policy)2>::~__shared_count (this=0x7f4c4c5b5f28, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr_base.h:733
	#8  std::__shared_ptr<crucible::IOHandle, (__gnu_cxx::_Lock_policy)2>::~__shared_ptr (this=0x7f4c4c5b5f20, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr_base.h:1183
	#9  std::shared_ptr<crucible::IOHandle>::~shared_ptr (this=0x7f4c4c5b5f20, __in_chrg=<optimized out>) at /usr/include/c++/10/bits/shared_ptr.h:121
	#10 crucible::Fd::~Fd (this=0x7f4c4c5b5f20, __in_chrg=<optimized out>) at ../include/crucible/fd.h:46
	#11 BeesFileRange::file_size (this=0x7f4c4e5ba4a0) at bees-types.cc:156
	#12 0x0000555760513950 in operator<< (os=..., bfr=...) at bees-types.cc:80
	#13 0x000055576050d662 in std::function<void (std::ostream&)>::operator()(std::ostream&) const (__args#0=..., this=0x7f4c4e5b9f60) at /usr/include/c++/10/bits/std_function.h:622
	#14 BeesNote::get_status[abi:cxx11]() () at bees-trace.cc:165
	#15 0x00005557604c9676 in BeesContext::dump_status (this=0x5557611c4de0) at bees-context.cc:89
	#16 0x00005557605206fb in std::function<void ()>::operator()() const (this=this@entry=0x7f4c4c5b65f0) at /usr/include/c++/10/bits/std_function.h:622
	#17 crucible::catch_all(std::function<void ()> const&, std::function<void (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)> const&) (f=..., explainer=...) at error.cc:55
	#18 0x000055576050aaa7 in operator() (__closure=0x5557611c52c8) at bees-thread.cc:22
	#19 0x00007f4c501beed0 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
	#20 0x00007f4c502c8ea7 in start_thread (arg=<optimized out>) at pthread_create.c:477
	#21 0x00007f4c4febddef in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Fix by making BeesFileRange::m_fd really const (not just mutable),
then fix all the broken code referencing it.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
2021-12-11 15:35:50 -05:00
parent 26acc6adfd
commit fbf6b395c8
4 changed files with 24 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
src/bees-context.cc
View File

@ -187,20 +187,20 @@ BeesContext::is_root_ro(uint64_t root)
}
bool
BeesContext::dedup(const BeesRangePair &brp)
BeesContext::dedup(const BeesRangePair &brp_in)
{
// TOOLONG and NOTE can retroactively fill in the filename details, but LOG can't
BEESNOTE("dedup " << brp);
BEESNOTE("dedup " << brp_in);
brp.second.fd(shared_from_this());
if (is_root_ro(brp.second.fid().root())) {
// BEESLOGDEBUG("WORKAROUND: dst root is read-only in " << name_fd(brp.second.fd()));
if (is_root_ro(brp_in.second.fid().root())) {
// BEESLOGDEBUG("WORKAROUND: dst root " << (brp_in.second.fid().root()) << " is read-only);
BEESCOUNT(dedup_workaround_btrfs_send);
return false;
}
auto brp = brp_in;
brp.first.fd(shared_from_this());
brp.second.fd(shared_from_this());
BEESTOOLONG("dedup " << brp);
@ -725,23 +725,22 @@ BeesContext::scan_one_extent(const BeesFileRange &bfr, const Extent &e)
}
BeesFileRange
BeesContext::scan_forward(const BeesFileRange &bfr)
BeesContext::scan_forward(const BeesFileRange &bfr_in)
{
// What are we doing here?
BEESTRACE("scan_forward " << bfr);
BEESTRACE("scan_forward " << bfr_in);
BEESCOUNT(scan_forward);
Timer scan_timer;
// Silently filter out blacklisted files
if (is_blacklisted(bfr.fid())) {
if (is_blacklisted(bfr_in.fid())) {
BEESCOUNT(scan_blacklisted);
return bfr;
return bfr_in;
}
BEESNOTE("scan open " << bfr);
// Reconstitute FD
BEESNOTE("scan open " << bfr_in);
auto bfr = bfr_in;
bfr.fd(shared_from_this());
BEESNOTE("scan extent " << bfr);