Commit cc6db4e60116c1f76577b6850a35ae7de69a95b6
Committed by
Ingo Molnar
Ingo Molnar
1 parent
a33a052f19
Exists in
master
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4 other branches
futex: Correct futex_wait_requeue_pi() commentary
The state machine described in the comments wasn't updated with a follow-on fix. Address that and cleanup the corresponding commentary in the function. Signed-off-by: Darren Hart <dvhltc@us.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> LKML-Reference: <4A737C2A.9090001@us.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Showing 1 changed file with 10 additions and 13 deletions Side-by-side Diff
kernel/futex.c
| ... | ... | @@ -2102,11 +2102,11 @@ |
| 2102 | 2102 | * We call schedule in futex_wait_queue_me() when we enqueue and return there |
| 2103 | 2103 | * via the following: |
| 2104 | 2104 | * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue() |
| 2105 | - * 2) wakeup on uaddr2 after a requeue and subsequent unlock | |
| 2106 | - * 3) signal (before or after requeue) | |
| 2107 | - * 4) timeout (before or after requeue) | |
| 2105 | + * 2) wakeup on uaddr2 after a requeue | |
| 2106 | + * 3) signal | |
| 2107 | + * 4) timeout | |
| 2108 | 2108 | * |
| 2109 | - * If 3, we setup a restart_block with futex_wait_requeue_pi() as the function. | |
| 2109 | + * If 3, cleanup and return -ERESTARTNOINTR. | |
| 2110 | 2110 | * |
| 2111 | 2111 | * If 2, we may then block on trying to take the rt_mutex and return via: |
| 2112 | 2112 | * 5) successful lock |
| ... | ... | @@ -2114,7 +2114,7 @@ |
| 2114 | 2114 | * 7) timeout |
| 2115 | 2115 | * 8) other lock acquisition failure |
| 2116 | 2116 | * |
| 2117 | - * If 6, we setup a restart_block with futex_lock_pi() as the function. | |
| 2117 | + * If 6, return -EWOULDBLOCK (restarting the syscall would do the same). | |
| 2118 | 2118 | * |
| 2119 | 2119 | * If 4 or 7, we cleanup and return with -ETIMEDOUT. |
| 2120 | 2120 | * |
| ... | ... | @@ -2232,14 +2232,11 @@ |
| 2232 | 2232 | rt_mutex_unlock(pi_mutex); |
| 2233 | 2233 | } else if (ret == -EINTR) { |
| 2234 | 2234 | /* |
| 2235 | - * We've already been requeued, but we have no way to | |
| 2236 | - * restart by calling futex_lock_pi() directly. We | |
| 2237 | - * could restart the syscall, but that will look at | |
| 2238 | - * the user space value and return right away. So we | |
| 2239 | - * drop back with EWOULDBLOCK to tell user space that | |
| 2240 | - * "val" has been changed. That's the same what the | |
| 2241 | - * restart of the syscall would do in | |
| 2242 | - * futex_wait_setup(). | |
| 2235 | + * We've already been requeued, but cannot restart by calling | |
| 2236 | + * futex_lock_pi() directly. We could restart this syscall, but | |
| 2237 | + * it would detect that the user space "val" changed and return | |
| 2238 | + * -EWOULDBLOCK. Save the overhead of the restart and return | |
| 2239 | + * -EWOULDBLOCK directly. | |
| 2243 | 2240 | */ |
| 2244 | 2241 | ret = -EWOULDBLOCK; |
| 2245 | 2242 | } |