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Does read/write blocked system call put the process in TASK_UNINTERRUPTIBLE or TASK_INTERRUPTIBLE state?


By : Emanuel Acevedo
Date : October 16 2020, 06:10 AM
around this issue With read(2) or write(2) family syscalls, the type of sleep depends on the type of file that is being accessed. In the documentation you quoted, "slow" devices are those where a read/write will sleep interruptibly, and "fast" devices are those which will sleep uninterruptibly (the uninterruptible sleep state is named D for "Disk Wait", since originally read/write on disk files was the most common reason for this type of sleep).
Note that "blocking" technically refers only to interruptible sleep.
code :


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Is it possible to know if a process is waiting in Blocked state on a Receive() call on Linux?


By : StaticMike
Date : March 29 2020, 07:55 AM
Hope this helps If you want to know if your threads are blocked, or exactly what they are blocked on, you can either take a thread dump or use a tool like jvisualvm to attach to the process and take a look (in jvisualvm you would attach to the process, take a thread dump, and then look at the activity of each thread).

How is a process state updated to blocked state (TASK_INTERRUPTIBLE)?


By : user3571969
Date : March 29 2020, 07:55 AM
may help you . It's behaving similarly to what you describe, except the io callback is set before calling elv_add_request(). If we take the stack from the previous thread:
code :
 [<c027fac4>] error_code+0x74/0x7c
 [<c019ed65>] elv_next_request+0x6b/0x116
 [<e08335db>] scsi_request_fn+0x5e/0x26d [scsi_mod]
 [<c019ee6a>] elv_insert+0x5a/0x134
 [<c019efc1>] __elv_add_request+0x7d/0x82
 [<c019f0ab>] elv_add_request+0x16/0x1d
 [<e0e8d2ed>] pkt_generic_packet+0x107/0x133 [pktcdvd]
 [<e0e8d772>] pkt_get_disc_info+0x42/0x7b [pktcdvd]
 [<e0e8eae3>] pkt_open+0xbf/0xc56 [pktcdvd]
 [<c0168078>] do_open+0x7e/0x246
 [<c01683df>] blkdev_open+0x28/0x51
 [<c014a057>] __dentry_open+0xb5/0x160
 [<c014a183>] nameidata_to_filp+0x27/0x37
 [<c014a1c6>] do_filp_open+0x33/0x3b
 [<c014a211>] do_sys_open+0x43/0xc7
 [<c014a2cd>] sys_open+0x1c/0x1e
 [<c0102b82>] sysenter_past_esp+0x5f/0x85
pkt_generic_packet() 
  blk_execute_rq()
    initialize a 'struct completion' object
    set it as 'struct request->end_io_data'
    blk_execute_rq_nowait(..., blk_end_sync_rq) // that's the io callback
    wait_for_completion_io() //sets task to TASK_UNINTERRUPTIBLE, waits on the 'struct completion' object to be complete

 ...
 the io then happens, a possible scenario would then be:
   blk_end_request()
     blk_end_bidi_request()
       blk_finish_request()
         req->end_io() // This is blk_end_sync_rq
           blk_end_sync_rq()
             complete() // sets task to TASK_NORMAL, signals completion

What happens to a signal for a process in "D" state (or TASK_UNINTERRUPTIBLE)?


By : Alberto Baldo
Date : March 29 2020, 07:55 AM
around this issue
TASK_UNINTERRUPTIBLE: The proccess is waiting on certain special cases of event, such as completion of of a disk I/O. If signal is generated (including SIGSTOP and SIGKILL) for a process in this state, then the signal is not delivered until the process emerges from this state.

If you have One-to-One-Mapping of Kernel- and User-Threads, why isn't process be blocked, if it makes a system-call?


By : user3019716
Date : March 29 2020, 07:55 AM
I hope this helps . The kernel schedules the threads not the processes globally.
In a very general case when a process is made of just its main thread, we use a kind of shortcut in the manner of speaking and say that the kernel schedules those processes, but it is just a (very common) corner case.

Blocked system call doesn't let SIGKILL kill the process


By : tuannobita
Date : March 29 2020, 07:55 AM
help you fix your problem Sending a signal to a process just sets a respective flag for this signal.
When a process returns from kernel mode (e.g., when a system call returns), these flags are checked. If one of them was previously set, the respective action is taken.
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