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MIPS: __raw_spin_lock() may spin forever on ticket wrap.

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If the lock is not acquired and has to spin *and* the second attempt
to acquire the lock fails, the delay time is not masked by the ticket
range mask.  If the ticket number wraps around to zero, the result is
that the lock sampling delay is essentially infinite (due to casting
-1 to an unsigned int).

The fix: Always mask the difference between my_ticket and the current
ticket value before calculating the delay.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
David Daney 2009-03-27 10:07:02 -07:00 committed by Ralf Baechle
parent f5fd02a33e
commit 0e6826c73c
1 changed files with 4 additions and 4 deletions
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8
arch/mips/include/asm/spinlock.h
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@ -76,7 +76,7 @@ static inline void __raw_spin_lock(raw_spinlock_t *lock)
"2: \n" "2: \n"
" .subsection 2 \n" " .subsection 2 \n"
"4: andi %[ticket], %[ticket], 0x1fff \n" "4: andi %[ticket], %[ticket], 0x1fff \n"
"5: sll %[ticket], 5 \n" " sll %[ticket], 5 \n"
" \n" " \n"
"6: bnez %[ticket], 6b \n" "6: bnez %[ticket], 6b \n"
" subu %[ticket], 1 \n" " subu %[ticket], 1 \n"
@ -85,7 +85,7 @@ static inline void __raw_spin_lock(raw_spinlock_t *lock)
" andi %[ticket], %[ticket], 0x1fff \n" " andi %[ticket], %[ticket], 0x1fff \n"
" beq %[ticket], %[my_ticket], 2b \n" " beq %[ticket], %[my_ticket], 2b \n"
" subu %[ticket], %[my_ticket], %[ticket] \n" " subu %[ticket], %[my_ticket], %[ticket] \n"
" b 5b \n" " b 4b \n"
" subu %[ticket], %[ticket], 1 \n" " subu %[ticket], %[ticket], 1 \n"
" .previous \n" " .previous \n"
" .set pop \n" " .set pop \n"
@ -113,7 +113,7 @@ static inline void __raw_spin_lock(raw_spinlock_t *lock)
" ll %[ticket], %[ticket_ptr] \n" " ll %[ticket], %[ticket_ptr] \n"
" \n" " \n"
"4: andi %[ticket], %[ticket], 0x1fff \n" "4: andi %[ticket], %[ticket], 0x1fff \n"
"5: sll %[ticket], 5 \n" " sll %[ticket], 5 \n"
" \n" " \n"
"6: bnez %[ticket], 6b \n" "6: bnez %[ticket], 6b \n"
" subu %[ticket], 1 \n" " subu %[ticket], 1 \n"
@ -122,7 +122,7 @@ static inline void __raw_spin_lock(raw_spinlock_t *lock)
" andi %[ticket], %[ticket], 0x1fff \n" " andi %[ticket], %[ticket], 0x1fff \n"
" beq %[ticket], %[my_ticket], 2b \n" " beq %[ticket], %[my_ticket], 2b \n"
" subu %[ticket], %[my_ticket], %[ticket] \n" " subu %[ticket], %[my_ticket], %[ticket] \n"
" b 5b \n" " b 4b \n"
" subu %[ticket], %[ticket], 1 \n" " subu %[ticket], %[ticket], 1 \n"
" .previous \n" " .previous \n"
" .set pop \n" " .set pop \n"