On Sun, 1 Feb 2004, Abramo Bagnara wrote:
Jaroslav Kysela ha scritto:
Modified Files:
rawmidi.c Log Message:
copy_*_user() function cannot be called from spinlock context
Index: rawmidi.c =================================================================== RCS file: /cvsroot/alsa/alsa-kernel/core/rawmidi.c,v retrieving revision 1.40 retrieving revision 1.41 diff -u -r1.40 -r1.41 --- rawmidi.c 23 Oct 2003 14:34:52 -0000 1.40 +++ rawmidi.c 1 Feb 2004 16:34:28 -0000 1.41 @@ -909,10 +909,11 @@ if (kernel) { memcpy(buf + result, runtime->buffer + runtime->appl_ptr, count1); } else { + spin_unlock_irqrestore(&runtime->lock, flags); if (copy_to_user(buf + result, runtime->buffer + runtime->appl_ptr, count1)) { - spin_unlock_irqrestore(&runtime->lock, flags); return result > 0 ? result : -EFAULT; } + spin_lock_irqsave(&runtime->lock, flags); } runtime->appl_ptr += count1; runtime->appl_ptr %= runtime->buffer_size; @@ -1133,10 +1134,13 @@ if (kernel) { memcpy(runtime->buffer + runtime->appl_ptr, buf, count1); } else { + spin_unlock_irqrestore(&runtime->lock, flags); if (copy_from_user(runtime->buffer + runtime->appl_ptr, buf, count1)) { + spin_lock_irqsave(&runtime->lock, flags); result = result > 0 ? result : -EFAULT; goto __end; } + spin_lock_irqsave(&runtime->lock, flags); } runtime->appl_ptr += count1; runtime->appl_ptr %= runtime->buffer_size;
With this patch you break write and read atomicity, you should:
1) read and save appl_ptr 2) update appl_ptr and avail 3) leave critical area 4) copy from/to user using saved appl_ptr
But hardware can overwrite data (read) or send data which are not yet available (write) when we are not in the spinlock context and data are not copied.
I see.
If we need atomic read() and write() we must probably add a semaphore.
Too heavyweight, I propose:
1) size_t ptr = appl_ptr_next 2) update appl_ptr_next etc. 3) pending++ 4) spin_unlock 5) copy from/to user 6) spin_lock 7) if (--pending) appl_ptr = appl_ptr_next
-- Abramo Bagnara mailto:[EMAIL PROTECTED]
Opera Unica Phone: +39.0546.656023 Via Emilia Interna, 140 48014 Castel Bolognese (RA) - Italy
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