path: root/arch
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authorSuresh Siddha <sbsiddha@gmail.com>2014-02-02 22:56:23 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-03-23 21:38:19 -0700
commitd2c6966a096ad50c33825a52e6521102ffeda1ff (patch)
tree7dfa9956e20278d16715b57ceaf8323547e10f97 /arch
parent535dba0ec5df095ce7aca036f78110356187c419 (diff)
x86, fpu: Check tsk_used_math() in kernel_fpu_end() for eager FPU
commit 731bd6a93a6e9172094a2322bd0ee964bb1f4d63 upstream. For non-eager fpu mode, thread's fpu state is allocated during the first fpu usage (in the context of device not available exception). This (math_state_restore()) can be a blocking call and hence we enable interrupts (which were originally disabled when the exception happened), allocate memory and disable interrupts etc. But the eager-fpu mode, call's the same math_state_restore() from kernel_fpu_end(). The assumption being that tsk_used_math() is always set for the eager-fpu mode and thus avoid the code path of enabling interrupts, allocating fpu state using blocking call and disable interrupts etc. But the below issue was noticed by Maarten Baert, Nate Eldredge and few others: If a user process dumps core on an ecrypt fs while aesni-intel is loaded, we get a BUG() in __find_get_block() complaining that it was called with interrupts disabled; then all further accesses to our ecrypt fs hang and we have to reboot. The aesni-intel code (encrypting the core file that we are writing) needs the FPU and quite properly wraps its code in kernel_fpu_{begin,end}(), the latter of which calls math_state_restore(). So after kernel_fpu_end(), interrupts may be disabled, which nobody seems to expect, and they stay that way until we eventually get to __find_get_block() which barfs. For eager fpu, most the time, tsk_used_math() is true. At few instances during thread exit, signal return handling etc, tsk_used_math() might be false. In kernel_fpu_end(), for eager-fpu, call math_state_restore() only if tsk_used_math() is set. Otherwise, don't bother. Kernel code path which cleared tsk_used_math() knows what needs to be done with the fpu state. Reported-by: Maarten Baert <maarten-baert@hotmail.com> Reported-by: Nate Eldredge <nate@thatsmathematics.com> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Suresh Siddha <sbsiddha@gmail.com> Link: http://lkml.kernel.org/r/1391410583.3801.6.camel@europa Cc: George Spelvin <linux@horizon.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
1 files changed, 12 insertions, 3 deletions
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index f7ea30dce23..b03ff184254 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -86,10 +86,19 @@ EXPORT_SYMBOL(__kernel_fpu_begin);
void __kernel_fpu_end(void)
- if (use_eager_fpu())
- math_state_restore();
- else
+ if (use_eager_fpu()) {
+ /*
+ * For eager fpu, most the time, tsk_used_math() is true.
+ * Restore the user math as we are done with the kernel usage.
+ * At few instances during thread exit, signal handling etc,
+ * tsk_used_math() is false. Those few places will take proper
+ * actions, so we don't need to restore the math here.
+ */
+ if (likely(tsk_used_math(current)))
+ math_state_restore();
+ } else {
+ }