[PATCH] Fix synchronous writers to wait properly for the result
Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz> points out a bug in ll_rw_block() usage. Typical usage is: mark_buffer_dirty(bh); ll_rw_block(WRITE, 1, &bh); wait_on_buffer(bh); the problem is that if the buffer was locked on entry to this code sequence (due to in-progress I/O), ll_rw_block() will not wait, and start new I/O. So this code will wait on the _old_ I/O, and will then continue execution, leaving the buffer dirty. It turns out that all callers were only writing one buffer, and they were all waiting on that writeout. So I added a new sync_dirty_buffer() function: void sync_dirty_buffer(struct buffer_head *bh) { lock_buffer(bh); if (test_clear_buffer_dirty(bh)) { get_bh(bh); bh->b_end_io = end_buffer_io_sync; submit_bh(WRITE, bh); } else { unlock_buffer(bh); } } which allowed a fair amount of code to be removed, while adding the desired data-integrity guarantees. UFS has its own wrappers around ll_rw_block() which got in the way, so this operation was open-coded in that case.
Showing
Please register or sign in to comment