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UPSTREAM: mm: madvise: return correct bytes advised with process_madvise

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Patch series "mm: madvise: return correct bytes processed with
process_madvise", v2.  With the process_madvise(), always choose to return
non zero processed bytes over an error.  This can help the user to know on
which VMA, passed in the 'struct iovec' vector list, is failed to advise
thus can take the decission of retrying/skipping on that VMA.

This patch (of 2):

The process_madvise() system call returns error even after processing some
VMA's passed in the 'struct iovec' vector list which leaves the user
confused to know where to restart the advise next.  It is also against
this syscall man page[1] documentation where it mentions that "return
value may be less than the total number of requested bytes, if an error
occurred after some iovec elements were already processed.".

Consider a user passed 10 VMA's in the 'struct iovec' vector list of which
9 are processed but one.  Then it just returns the error caused on that
failed VMA despite the first 9 VMA's processed, leaving the user confused
about on which VMA it is failed.  Returning the number of bytes processed
here can help the user to know which VMA it is failed on and thus can
retry/skip the advise on that VMA.

[1]https://man7.org/linux/man-pages/man2/process_madvise.2.html.

Link: https://lkml.kernel.org/r/cover.1647008754.git.quic_charante@quicinc.com
Link: https://lkml.kernel.org/r/125b61a0edcee5c2db8658aed9d06a43a19ccafc.1647008754.git.quic_charante@quicinc.com
Fixes: ecb8ac8b1f14("mm/madvise: introduce process_madvise() syscall: an external memory hinting API")
Signed-off-by: Charan Teja Kalla <quic_charante@quicinc.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: UtsavBalar1231 <utsavbalar1231@gmail.com>
Change-Id: Id743a28f41e28f4867bb5265be6ae7ef58bbc394
Signed-off-by: azrim <mirzaspc@gmail.com>
This commit is contained in:
Charan Teja Kalla 2022-03-22 14:46:44 -07:00 committed by azrim
parent 0b26fa6f0d
commit f97cfad544
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GPG Key ID: 497F8FB059B45D1C
1 changed files with 1 additions and 2 deletions
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mm/madvise.c
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@ -1273,8 +1273,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
iov_iter_advance(&iter, iovec.iov_len);
}
if (ret == 0)
ret = total_len - iov_iter_count(&iter);
ret = (total_len - iov_iter_count(&iter)) ? : ret;
release_mm:
mmput(mm);