linux/kernel, branch v2.6.33.6

tracing: Consolidate protection of reader access to the ring buffer

2010-07-05T18:16:10Z

commit 7e53bd42d14c75192b99674c40fcc359392da59d upstream. At the beginning, access to the ring buffer was fully serialized by trace_types_lock. Patch d7350c3f4569 gives more freedom to readers, and patch b04cc6b1f6 adds code to protect trace_pipe and cpu#/trace_pipe. But actually it is not enough, ring buffer readers are not always read-only, they may consume data. This patch makes accesses to trace, trace_pipe, trace_pipe_raw cpu#/trace, cpu#/trace_pipe and cpu#/trace_pipe_raw serialized. And removes tracing_reader_cpumask which is used to protect trace_pipe. Details: Ring buffer serializes readers, but it is low level protection. The validity of the events (which returns by ring_buffer_peek() ..etc) are not protected by ring buffer. The content of events may become garbage if we allow another process to consume these events concurrently: A) the page of the consumed events may become a normal page (not reader page) in ring buffer, and this page will be rewritten by the events producer. B) The page of the consumed events may become a page for splice_read, and this page will be returned to system. This patch adds trace_access_lock() and trace_access_unlock() primitives. These primitives allow multi process access to different cpu ring buffers concurrently. These primitives don't distinguish read-only and read-consume access. Multi read-only access is also serialized. And we don't use these primitives when we open files, we only use them when we read files. Signed-off-by: Lai Jiangshan LKML-Reference: <4B447D52.1050602@cn.fujitsu.com> Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman

perf: Fix signed comparison in perf_adjust_period()

2010-07-05T18:16:07Z

commit f6ab91add6355e231e1c47897027b2a6ee4fa268 upstream. Frederic reported that frequency driven swevents didn't work properly and even caused a division-by-zero error. It turns out there are two bugs, the division-by-zero comes from a failure to deal with that in perf_calculate_period(). The other was more interesting and turned out to be a wrong comparison in perf_adjust_period(). The comparison was between an s64 and u64 and got implicitly converted to an unsigned comparison. The problem is that period_left is typically < 0, so it ended up being always true. Cure this by making the local period variables s64. Reported-by: Frederic Weisbecker Tested-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra LKML-Reference: Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

signals: check_kill_permission(): don't check creds if same_thread_group()

2010-07-05T18:15:56Z

commit 065add3941bdca54fe04ed3471a96bce9af88793 upstream. Andrew Tridgell reports that aio_read(SIGEV_SIGNAL) can fail if the notification from the helper thread races with setresuid(), see http://samba.org/~tridge/junkcode/aio_uid.c This happens because check_kill_permission() doesn't permit sending a signal to the task with the different cred->xids. But there is not any security reason to check ->cred's when the task sends a signal (private or group-wide) to its sub-thread. Whatever we do, any thread can bypass all security checks and send SIGKILL to all threads, or it can block a signal SIG and do kill(gettid(), SIG) to deliver this signal to another sub-thread. Not to mention that CLONE_THREAD implies CLONE_VM. Change check_kill_permission() to avoid the credentials check when the sender and the target are from the same thread group. Also, move "cred = current_cred()" down to avoid calling get_current() twice. Note: David Howells pointed out we could relax this even more, the CLONE_SIGHAND (without CLONE_THREAD) case probably does not need these checks too. Roland said: : The glibc (libpthread) that does set*id across threads has : been in use for a while (2.3.4?), probably in distro's using kernels as old : or older than any active -stable streams. In the race in question, this : kernel bug is breaking valid POSIX application expectations. Reported-by: Andrew Tridgell Signed-off-by: Oleg Nesterov Acked-by: Roland McGrath Acked-by: David Howells Cc: Eric Paris Cc: Jakub Jelinek Cc: James Morris Cc: Roland McGrath Cc: Stephen Smalley Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

mutex: Fix optimistic spinning vs. BKL

2010-07-05T18:15:33Z

commit fd6be105b883244127a734ac9f14ae94a022dcc0 upstream. Currently, we can hit a nasty case with optimistic spinning on mutexes: CPU A tries to take a mutex, while holding the BKL CPU B tried to take the BLK while holding the mutex This looks like a AB-BA scenario but in practice, is allowed and happens due to the auto-release on schedule() nature of the BKL. In that case, the optimistic spinning code can get us into a situation where instead of going to sleep, A will spin waiting for B who is spinning waiting for A, and the only way out of that loop is the need_resched() test in mutex_spin_on_owner(). This patch fixes it by completely disabling spinning if we own the BKL. This adds one more detail to the extensive list of reasons why it's a bad idea for kernel code to be holding the BKL. Signed-off-by: Tony Breeds Acked-by: Linus Torvalds Acked-by: Peter Zijlstra Cc: Benjamin Herrenschmidt LKML-Reference: <20100519054636.GC12389@ozlabs.org> [ added an unlikely() attribute to the branch ] Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

cpumask: fix compat getaffinity

2010-07-05T18:15:30Z

commit fa9dc265ace9774e62f0e31108e5f47911124bda upstream. Commit a45185d2d "cpumask: convert kernel/compat.c" broke libnuma, which abuses sched_getaffinity to find out NR_CPUS in order to parse /sys/devices/system/node/node*/cpumap. On NUMA systems with less than 32 possibly CPUs, the current compat_sys_sched_getaffinity now returns '4' instead of the actual NR_CPUS/8, which makes libnuma bail out when parsing the cpumap. The libnuma call sched_getaffinity(0, bitmap, 4096) at first. It mean the libnuma expect the return value of sched_getaffinity() is either len argument or NR_CPUS. But it doesn't expect to return nr_cpu_ids. Strictly speaking, userland requirement are 1) Glibc assume the return value mean the lengh of initialized of mask argument. E.g. if sched_getaffinity(1024) return 128, glibc make zero fill rest 896 byte. 2) Libnuma assume the return value can be used to guess NR_CPUS in kernel. It assume len-arg Acked-by: Rusty Russell Acked-by: Arnd Bergmann Reported-by: Ken Werner Cc: Andi Kleen Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

posix_timer: Fix error path in timer_create

2010-07-05T18:15:29Z

commit 45e0fffc8a7778282e6a1514a6ae3e7ae6545111 upstream. Move CLOCK_DISPATCH(which_clock, timer_create, (new_timer)) after all posible EFAULT erros. *_timer_create may allocate/get resources. (for example posix_cpu_timer_create does get_task_struct) [ tglx: fold the remove crappy comment patch into this ] Signed-off-by: Andrey Vagin Cc: Oleg Nesterov Cc: Pavel Emelyanov Reviewed-by: Stanislaw Gruszka Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

Fix racy use of anon_inode_getfd() in perf_event.c

2010-07-05T18:15:28Z

commit ea635c64e007061f6468ece5cc9cc62d41d4ecf2 upstream. once anon_inode_getfd() is called, you can't expect *anything* about struct file that descriptor points to - another thread might be doing whatever it likes with descriptor table at that point. Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman

profile: fix stats and data leakage

2010-05-26T21:32:09Z

commit 16a2164bb03612efe79a76c73da6da44445b9287 upstream. If the kernel is large or the profiling step small, /proc/profile leaks data and readprofile shows silly stats, until readprofile -r has reset the buffer: clear the prof_buffer when it is vmalloc()ed. Signed-off-by: Hugh Dickins Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

revert "procfs: provide stack information for threads" and its fixup commits

2010-05-26T21:32:04Z

commit 34441427aab4bdb3069a4ffcda69a99357abcb2e upstream. Originally, commit d899bf7b ("procfs: provide stack information for threads") attempted to introduce a new feature for showing where the threadstack was located and how many pages are being utilized by the stack. Commit c44972f1 ("procfs: disable per-task stack usage on NOMMU") was applied to fix the NO_MMU case. Commit 89240ba0 ("x86, fs: Fix x86 procfs stack information for threads on 64-bit") was applied to fix a bug in ia32 executables being loaded. Commit 9ebd4eba7 ("procfs: fix /proc//stat stack pointer for kernel threads") was applied to fix a bug which had kernel threads printing a userland stack address. Commit 1306d603f ('proc: partially revert "procfs: provide stack information for threads"') was then applied to revert the stack pages being used to solve a significant performance regression. This patch nearly undoes the effect of all these patches. The reason for reverting these is it provides an unusable value in field 28. For x86_64, a fork will result in the task->stack_start value being updated to the current user top of stack and not the stack start address. This unpredictability of the stack_start value makes it worthless. That includes the intended use of showing how much stack space a thread has. Other architectures will get different values. As an example, ia64 gets 0. The do_fork() and copy_process() functions appear to treat the stack_start and stack_size parameters as architecture specific. I only partially reverted c44972f1 ("procfs: disable per-task stack usage on NOMMU") . If I had completely reverted it, I would have had to change mm/Makefile only build pagewalk.o when CONFIG_PROC_PAGE_MONITOR is configured. Since I could not test the builds without significant effort, I decided to not change mm/Makefile. I only partially reverted 89240ba0 ("x86, fs: Fix x86 procfs stack information for threads on 64-bit") . I left the KSTK_ESP() change in place as that seemed worthwhile. Signed-off-by: Robin Holt Cc: Stefani Seibold Cc: KOSAKI Motohiro Cc: Michal Simek Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

CRED: Fix a race in creds_are_invalid() in credentials debugging

2010-05-12T22:02:50Z

commit e134d200d57d43b171dcb0b55c178a1a0c7db14a upstream. creds_are_invalid() reads both cred->usage and cred->subscribers and then compares them to make sure the number of processes subscribed to a cred struct never exceeds the refcount of that cred struct. The problem is that this can cause a race with both copy_creds() and exit_creds() as the two counters, whilst they are of atomic_t type, are only atomic with respect to themselves, and not atomic with respect to each other. This means that if creds_are_invalid() can read the values on one CPU whilst they're being modified on another CPU, and so can observe an evolving state in which the subscribers count now is greater than the usage count a moment before. Switching the order in which the counts are read cannot help, so the thing to do is to remove that particular check. I had considered rechecking the values to see if they're in flux if the test fails, but I can't guarantee they won't appear the same, even if they've changed several times in the meantime. Note that this can only happen if CONFIG_DEBUG_CREDENTIALS is enabled. The problem is only likely to occur with multithreaded programs, and can be tested by the tst-eintr1 program from glibc's "make check". The symptoms look like: CRED: Invalid credentials CRED: At include/linux/cred.h:240 CRED: Specified credentials: ffff88003dda5878 [real][eff] CRED: ->magic=43736564, put_addr=(null) CRED: ->usage=766, subscr=766 CRED: ->*uid = { 0,0,0,0 } CRED: ->*gid = { 0,0,0,0 } CRED: ->security is ffff88003d72f538 CRED: ->security {359, 359} ------------[ cut here ]------------ kernel BUG at kernel/cred.c:850! ... RIP: 0010:[] [] __invalid_creds+0x4e/0x52 ... Call Trace: [] copy_creds+0x6b/0x23f Note the ->usage=766 and subscr=766. The values appear the same because they've been re-read since the check was made. Reported-by: Roland McGrath Signed-off-by: David Howells Signed-off-by: James Morris Signed-off-by: Greg Kroah-Hartman