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1. Userspace sends the command "losetup -d" which uses the open() call
to open the device
2. Kernel receives the ioctl command "LOOP_CLR_FD" which calls the
function loop_clr_fd()
3. If LOOP_CLR_FD is the first command received at the time, then the
AUTOCLEAR flag is not set and deletion of the
loop device proceeds ahead and scans the partitions (drop/add
partitions)
if (disk_openers(lo->lo_disk) > 1) {
lo->lo_flags |= LO_FLAGS_AUTOCLEAR;
loop_global_unlock(lo, true);
return 0;
}
4. Before scanning partitions, it will check to see if any partition of
the loop device is currently opened
5. If any partition is opened, then it will return EBUSY:
if (disk->open_partitions)
return -EBUSY;
6. So, after receiving the "LOOP_CLR_FD" command and just before the above
check for open_partitions, if any other command
(like blkid) opens any partition of the loop device, then the partition
scan will not proceed and EBUSY is returned as shown in above code
7. But in "__loop_clr_fd()", this EBUSY error is not propagated
8. We have noticed that this is causing the partitions of the loop to
remain stale even after the loop device is detached resulting in the
IO errors on the partitions
Fix:
Defer the detach of loop device to release function, which is called when
the last close happens, by setting the lo_flags to LO_FLAGS_AUTOCLEAR at
the time of detach i.e in loop_clr_fd() function.
Test case involves the following two scripts:
script1.sh:
while [ 1 ];
do
losetup -P -f /home/opt/looptest/test10.img
blkid /dev/loop0p1
done
script2.sh:
while [ 1 ];
do
losetup -d /dev/loop0
done
Without fix, the following IO errors have been observed:
kernel: __loop_clr_fd: partition scan of loop0 failed (rc=-16)
kernel: I/O error, dev loop0, sector 20971392 op 0x0:(READ) flags 0x80700
phys_seg 1 prio class 0
kernel: I/O error, dev loop0, sector 108868 op 0x0:(READ) flags 0x0
phys_seg 1 prio class 0
kernel: Buffer I/O error on dev loop0p1, logical block 27201, async page
read
Signed-off-by: Gulam Mohamed <gulam.mohamed@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240618164042.343777-1-gulam.mohamed@oracle.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.